Taylor & Frafl5 Group
v/an PaiIialagv (August 2008) 37(4), 44 4
Mycobacteriosis in naturally infected ring-neck doves
(Streptopelia risoria): investigation of the association
between feather colour and susceptibility to infection,
disease and lesions type
Miguel D. Saggesel2*, Ian Tizard' and David N. Phalen"3
'The Schithot Exotic Bird Health Center, Department of Veierinari' Pathohiologt', College oJ Veierinw-v Medicine and
Biomedical .Sciences, Texas A & M Unirersirv, 4467 TA MU College Station, TX 77843-4467, USA. 'College of
Veiei'inarr Medicine, Western Unirersiiv of Health Sciences, Pomona. CA 91766. USA, and 3The Wildlife Health (111(1
Conservation Centre, Unitersiti' of' Sidney, Camden, Neic South Wales 4475, Australia
Prevalence of infection and disease. the degree of organ involvement and the nature of the lesions were
investigated in 11 white and 18 non-white ring-neck doves coming from a flock naturally infected with
lvi vcoha cteriuin ui/mn subsp. ac/mn. Lesions were common in the liver, spleen, lung. kidney, intestines, ovary
and bone marrow. Overall, 18 out of 29 (62) birds were considered infected with a sequevar of M. arjuni
subsp. ar/u/n that contains serotypes 2. 3, 4 and 9. The prevalence of infection in the white doves (36.4 1V) was
significantly lower than in the non-white morphs (77,77). White doves had on average fewer organs affected
(mean = 3.1) than the non-white doves (mean = 5.9). A diffuse pattern of inflammation in the liver and
spleen was observed mainly in non-white doves. Focal or mu]iift)cal granulomatous inflammation of the liver
and spleen was predominant in white doves. Genetic mechanisms of immunity to mycobacteriosis may be
contributing or determining these differences. There are three basic colour morphs in ring-neck doves—dark
or wild type, blond and white—and the alleles coding for colour are sex-linked and located on the sex (Z)
chromosome. Female's single sexual chromosomed (ZW) and homozygous males (ZZ) can be white if they
carry the white alleles. It is very probable that the gene or genes modulating the immune response to M.
ar/unl subsp. ai'/wn infection in these doves could be associated to these loci or at least located in the same
(Z) chromosome, as the association with white colour suggests.
Mycobacteriosis is a relatively common cause of disease
in pet, avicultural. zoo and free-ranging birds (Montali
c/cd.. 1976; Tell ci cii.. 2001: Pollock, 2006: Converse,
2007). Most cases of mycobacteriosis are caused by
Mi'c'ohaeieriuin aria/n sLibsp, cniiini and Mi'cohacterium
genai'c'nse, although other species of mycobacteria such
as Mvcobacteriuni iuhercu/osis. Mycobacterium br/ui-
tam, Mi'cohaeternan gorcioncie. Mi'cobaelerniiii iio,,cliw-
mogenicu/n. Mtc'obacteriuni si/iliac and Micohcicteriwn
cciatuni may also infect birds (Hoop ci al., 1996; Tell
ci al., 2001: Bertelsen ci al., 2006: Steinmetz ci cii..
2006: Travis ci cii.. 2007). The pathogenesis of natural
avian mycobacteriosis has been minimally investigated
(Hejlicek & Treml. 1995: Cromie ci cii.. 2000: Tell etc/i..
2001, 2003) and many aspects of the disease remain
Although reports of mycobacteriosis exist for most
orders of birds, susceptibility, prevalence of infection
and diseases, the degree of organ involvement and the
nature of the lesions vary widely (Montali ci al.. 1976:
Hejlicek & Treml. 1995; Cromie ci cli.. 2000: Friend,
2001; Tell ci al., 2001: Schmidt ci al., 2003; Pollock,
2006; Converse, 2007). Environmental factors have been
proposed to explain different susceptibility (Montali ci
al.. 1976: Tell ci al., 2001; Pollock, 2006). Malnutrition.
overcrowding, concurrent diseases, and poor hygiene
alone or combined are potential stressors that may
predispose birds to mycobacteriosis. 1-lowever, environ-
mental factors do not explain completely the different
susceptibility of birds to mycohacteriosis. Not all birds
housed in the same facilities and under the same
management Practices become infected and develop
disease (Cromie ci cii.. 1991. 1992: M. D. Saggese,
unpublished data) and their response to these different
stressors may vary.
Variations in the pathology of natural and experi-
mental infection, the degree of organ involvement and
the nature of the lesions of mycohacteriosis has been
attributed either to characteristics of the agent. to the
stage of the disease or to the bird's immune response
(Montali ci cii.. 1976: Cromie et al., 2000; Schmidt cicd.,
2003). Limited studies suggest that host genetic factors
*To whom correspondence should he addressed. Tel: + 1 909 706 3532. E-mail: firstname.lastname@example.org
Received 24 March 2008
ISSN 0307-9457 (print) ISSN 1465-3338 (online) 08 40443-08?
DO!: 10,1050 03079450802210655
2008 Houghton Trust lid
444 M. D. Sarrgesc cl
play a major role in determining susceptibility to avian
mycohacteriosis (Cromic ci al.. 1991. 1992: Eiejlicek &
Trernl. 1995). A differential susceptibility to mycohacter-
iosis, reflected by the number of affected birds and the
nature of their lesions, has been demonstrated in two
chicken lines challenged with M. at/mn (Gross ci al.,
1989). Recently, genetic susceptibility has also been
suggested as a predisposing cause of disease and the
nature of lesions in captive white winged-ducks and two
species of doves (Cromie ci (i!. 1991. 1992: Saggese &
Phalen, 2005: Saggese ci al., 2007).
Pigeons and doves (Order Columbiformes) are con-
sidered particularly susceptible to avian mycobacteriosis
(Feldman, 1938; Francis, 1958: Van der Schaf ci al.,
1976: Montali ci al., 1976: Pond & Rush. 1981:
Bougiouk]is ci al., 2005). Other authors, however.
consider some species of pigeon and doves to be highly
resistant to experimental and natural infection (H(Jlicck
& Treml, 1993, 1995). These contrasting opinions may
be explained both by genetic factors as well as by local
environmental and other risk factors. In one study,
differences in species susceptibility to natural and
experimental infection with M. whim were observed in
collared doves (Sircpiopelia dccaacto) and turtle doves
(Sircptopclia tu;'iur) (Hejlicek & Treml, 1993). The
former were found to be highly susceptible while the
related turtle doves were resistant (HejlIcek & Trernl,
Other evidence for a possible genetic component for
this different susceptibility comes from a natural out-
break of mycobacteriosis in Texas in 1998. A flock
containing diamond doves (Gcopclia cuneala) as well as
two different colour morphs (white and wild-type) of
ring-neck doves (Strcpiopelia risoria), showed significant
differences in organ involvement, distribution and his-
topathologic lesions and serologic responses (Saggesc &
Phalen, 2005). While all three groups of doves presented
with microscopic lesions in the liver and the spleen,
lesions in the intestines, bone marrow and lungs were
found only in wild-type ring-neck doves. Nil ultifocal
granulomatous hepatitis was observed in all of the birds,
but it granulomatous hepatitis was only observed
in the wild-type doves (Saggese & Phalen. 2005). The
finding, by polyrnerase chain reaction (PCR) and
sequencing of the dnaf gene. of the same M. whim
subsp. ai'iwn in these doves and in the shared environ-
ment in which these birds were housed suggested that
these variations were not due to different organisms or to
differences in exposure. Furthermore, the absence of
antibodies (as detected by complement fixation) in the
white rin g-neck doves compared with seropositivity in
wild-type and diamond doves suggested that a different
humoral immune response occurred in these birds. This
also supports the suggestion that differences in the
pathogenesis and immune response were associated
with colour. Although the number of birds in this study
was small, and several variables were not formally
controlled, precluding a statistical analysis, these data
together with previous studies (Hejlicek & Treml 1993.
1995) suggested the possibility that differences in sus-
ceptibility and pathology of mycobacterial infections
may occur in ring-neck doves with different coloLir
morphs, and points to a possible association between
genes coding for feather colour and susceptibility to
Ring-neck doves present in several colour morphs.
obtained by natural or artificial selection. The genetics
of these colour mutations in these species have been
analysed (Miller, 2007). Identifying and understanding
differences in pathogenesis and susceptibility to nlyco-
bacteriosis in closely related species or strains of birds
could assist identification of the genes involved in
differential susceptibility and pathogenesis. The occur-
rence in Texas of a captive Population of' ring-neck
doves, including individuals of different colour morphs,
suffering from avian mycobacteriosis offered ail
to investigate the presentation of this disease in a
large number of birds and to look for evidence of
differential susceptibility. We hypothesized that lesion
type and distribution and susceptibility to infection and
disease of naturally infected ring-neck doves would be
different in white doves compared with other colour
niorphs. Therefore, the main goals of this study were to
investigate the prevalence of mycobacterial infection and
disease in the different colour morphs found in this
flock: to describe and characterize the gross and micro-
scopic lesions in affected birds; to identify the species
and sequevar of' mycobacteria involved: and to deter-
mine whether an association exists between susceptibility
to this infection and disease, lesion characteristics and
feather colour morphs of ring-neck doves.
Materials and Methods
Specimens. Seventy adult ring-neck doves were obtained from an aviary
neat- l-lillshor-o, TexaS. USA in July 2005. These birds came from a flock
where more than 60 doves had died during the previous 6 months.
Mycobacterral infection had been previousl y confirmed in these birds at
the Texas Veterinary Medical Diagnostic Laboratory (College Station.
Texas. USA) and the condition of SOC of the survivin g birds
(decreased productivity, weight loss. depi'ession) was consistent with
nivcohacleriosis. These birds were all housed in it sited that was
open to and surrounded on two sides by an outdoor flight. There was
heavy faecal contamination
ion ot the floor Lind perching su faces of the
shed. Food and writer were contaminated with faeces. The surviving
birds were donated and transferred to an isolation building at the
College of Veterinary Medicine and Biomedical Sciences, Texas A&M
University (College Station. Texas. USA)- During the following 2
weeks. 29 birds (It white, eight blond, six pied, one orrtnge, two wild-
type and one white-silky coloured) (Oliver . 2005: Miller, 2007) were
randomly selected, anaesthetized by intramuscular injection of keta-
mine and xylazine. and euthanized by exsanguination through eardio-
Doves acre necropsied and samples collected within 4 It of
euthanasia. Tissues were collected for PCR using cleaned. autoclaved
instruments that had been treated with bleach and forinalin - A different
set of instruments was used to collect tissues from each bud and organ
to prevent DNA carryover. Samples of the liver, spleen, lung, bone
marrow and of other organs with gross lesions were collected and frozen
For PCR rind culture. The liver, spleen, mug. trachea. heart. kidney,
oesophagus. crop. proventriculus, ventriculus. intestines. gonads, pan-
creas and skeletal muscle were examined for lesions consistent with
myeohaeteriosis. Specimens from these organs were fornialin-fixed rind
pit raffin-einbedded and stained with hriematoxylin and eosin and Ziehl
Microscopically. inflammatory lesions were scored scniiqurtntitatively
as mild. moderate and severe based on the number of inhlainmritory cells
within the lesions and the area of tissue affected. I hist opal hological
changes compatible with mycohacteriosis were described and classified
as focal/multiihcal gramiulomatous. consisting of svehl-defined foci of
inflammatory cells ..s()iaetines strrrounded b y a ring of hbm'ous tissue and
with (sometimes without) a variable amount of ccii trrrl caseous necrosis,
or classified as diffuse granulomat ous inflammnatirrn. with it
degree of diffuse in llrimmritory cell infiltration without formation of
discrete foci or nodules, absence of a fibrous cripsule and little or no
NI 'cohacleriosts in ring-neck doves 445
caseous necrosis. The numbers ol acid-fast bacilli were subjectively
graded as none, few. many or massive. Congo red staining was employed
to investigate the presence of amyloid in the liver and spleen.
Immediately after the birds were euthanized, additional tissue samples
were collected using the biopsy techniques employed in live birds. Bone
marrow aspirates, using a 20 G needle and 6 ml syringe, were obtained
from the distal ulna. A bone marrow smear was made. heat-fixed and the
remaining sample saved at SO C. The celomic cavity was opened
aseptically through a inidline ventral approach and it piece of liver
approximately (4 mm a 4 nim x 4 mm) was excised from the caudal
border of the right lobe. This is the location and size of tissue that would
be collected from a live bird of this size during a routine liver biopsy. A
small portion was saved for PCR and culture, and the remaining tissue
fornialin-fixed for histological examination. The duodenum was identi-
fied and aspirated with a 25 G needle and I nil syringe. A portion of the
aspirated material was smeared onto a glass slide. heat-fixed and Zichl-
Neelsen stained. Bone tiiarrow 'aspirates and "biopsied" liver were
stained svidi Ziehl Ncelsen, cultured and tested by PCR.
Detection of nivcobacteriii in tissues. Swabs from the investigated tissues
from all of the doves were inoculated into S ml M iddlebroock 7119
broth (Becton Dickinson. Franklin Lakes. New Jerse y. USA) containing
0.5' (',/v ) glycerol and 10/ )v/s') oleic acid albumin, and incubated at
39 C followin g myeobacteritl culture standards (Million ci al.. 2007).
Cultures svei'e inspected weekly for microbial growth and examined for
the presence of mvcobacterta by Ziehl Neelsen staining.
DNA was extracted from all of the investigated tissues using
the Puregene 5 Genomic DNA Purification Kit )Gentra Systems.
Minneapolis, Minnesota. LISA) following the instructions of the
manufacturer. PCR screcnnig for mscobacterial DNA was performed
using primers TI )5-GGGTGACGCG(G/A )CATGGC('CA-3') and
T2 )5'-CCGGTTTCGTCGTA('TCCTJ'-3') for amplification of the
236-base-pair thma.l gene as described by Morita ci al. (2004). The I'CR
reaction pmrmtmeters were as follows: one initial cs dc of 94 C for 5m , 40
cycles at 94 C for 3)) sec. 60 C for 45 sec and 72 C for I mm: and an
additional elon gation step at 72 C for 5 tam. Positive (.11. (it him suhsp.
mmi'iuiii) and negalive reactioti control (DNA-RNA-free sterile water)
were utilijcd in each reaction. Amplified DNA was visualized after
elcctrophoresis on it 1.5/ ethidium bromide-stained agarose gel. PCR
Products were purified using the QlAquick i'CR Purification Kit
(Qimtgcn Inc.. Valencia. California. USA). Sequenemiig reactions were
performed using an AB1 Prism Big Die Terminator s3.)) Cycle
Sequencing Kit (Applied Biosystetiis inc., Foster City, California.
LISA). Nucleotide sequences were determined with an A1311100
automated DNA sequencer (Applied Biosystems Inc.). All sequences
were aligned using Clustal X 1.81 (Thompson c/ al.. 1997) and were
compared with sequences retrieved from (JeitBank )www.nehi.nlm.nih.-
gos /Genban k/index, lit nil).
Detailed information about the sensitivity and specificity of these
diagnostic tests and humoriml response in these doves has been described
elsewhere (NL D. Smiggese. unpublished data: P. Gras. unpublished
Infection and health status. C riteria for the classification of the diseased
status of the birds(diseased or healthy) were based upon the presence of
gross and microscopic lesions. A positive identification of mcobacteria
by culture and/or PCR or by the identificatioti of acid-fast organisms in
stained tissues or smears defined intcctioti status )infected or unin-
fected). Based on these criteria, four subcategories were identified:
diseased infected, birds with moderate to severe inflammation in one or
more organs and positive for mycohacteria: diseased uttinfectcd. birds
with mild lesions compatible with mycobacteriosis and negative for
mycohacteria: healthy uninfected. birds without lesions and negative for
mycobacterut: and healthy infected, birds without lesions and negative
for acid-fast bacilli in tissues but positive PCR and/or culture results.
Statistical analysis. 'rhe associatiott between white and non-white
coloured doves together with health and infection status, the number
of organs with lesions and the type of inflammation in the spleen and
liver was analysed using contingency tables and Fischer's exact test after
demonstration of normality using Kolmogom'ov Smirtiov. Shapiro Wilk
and [)'Agostino Peai'soti tests. Test statistics were considered signifi-
cant at P <0.05. All statistical analysis was conducted using the formula
package in Prism 5 for Windows )GraphPad Software. Inc.,' available
online at wvvwgraphipad.com(. This research was approved by the
ULAC'C/IAACI. IC at Texas A&M University )Aninial Use Protocol
Macroscopic findings. Twenty-nine doves were examined
by necropsy. The gender. colortr, health and infection
status of white and non-white colour morphs are
presented in Table I. Twelve doves were tiale and 17
doves were female. Nineteen birds (65.5',V,)) presented
with gross lesions compatible with i'nycobacteriosis. The
spleen and liver were most commonly affected, followed
by the intestines and the lungs. The heart, kidney. air
sacs and trachea were rarely grossly affected. Most
affected birds had multiple organ involvement. No
significant gross lesions were observed in the oesopha-
gus, proventriculus. ventt-iculus, gonads. pancreas, cen-
tral nervous system and skeletal muscle. Gross lesions in
the liver of most birds consisted of severe, diffuse, pale
orange tan discolouration and enlargement (Figure la).
In two birds, the liver was moderately enlarged and
contained single or multiple white--yellow nodules of
variable size (range I to 10 mm) embedded in the
parenchyma (Figure lb).
Gross lesions in the spleens consisted of one or more.
caseous, firm yellowish foci, of variable size. The largest
foci usually had a caseous central core. Splenomegaly
was observed in 13 birds, Focal or multi-focal caseous
nodules of variable size and number were found in the
lungs and kidneys. Diffuse thickening of the duodenum
and a variable number of yellow, round or oval-shaped
foci 2 to 5 mm in diameter were observed in the
Table I, P,'et'alence of' infection and diffuse and ,nulnJoe'al lesions in rh/k' and non-tm'Iutr' ring-neck doi'es (S. risoria)
Prevalence of birds?
Pattern of inflammation*
Mcmiii number of
White?II?2 male; 9 female?3.1?4111 (36.4%)?7/11 (63.6%)?I?
Non-white?18?10 male; S female?5.9?14/I8 (77.7%)?14/18 (77.7%)?12?11
n, sample size. Diseased'. doves with gross and/or microscopic lesions with disregard of infection status. Infected: doves with a positive
identification of myeohactcria by culture and/or PCR or by the identification of acid-last organisms in stained
*Differences statistically significant.
stained tissues or smears.
440?\1. 1). Siggc'c 'Vt iiI.
V V :.?
Figure I. icr Severe heparonzegalt' and orange-tan discolouration in 0 1TO1?-tiii!e ring-neck dare (S. risoria). l/). jl,f()(I4tVatC
hepatontegrej4v and inn/ti/neal hepatic granuloinas in a white ring-neck dole ic Multi/dial hepatitis in It While ring-neck dine
cV/nff4lcielVi:ed by li'niphovtic and Inst iocytzc infiltrates. A central core of necroctc ringed hi inulitnucleated giant cells cai he ohe,zed in
the right focus. id. Severe di7iice gr(11711101-11011-s hepatitis and deposits / anzi'loid in the Jiale/nIzInla n/a non-while ,ViIig_,lc_chV doze.
intestinal wall or protruding on the serosal surface in II
birds. These foci were usually more numerous and
evident, in the duodenum but they were also observed
along the jejunum, ileum and colon. Five birds presented
with ascites. Diffuse air saculitis and pericarditis were
additional findings in three birds. Gross lesions were not
observed iii the remaining organs.
Microscopic findings. Twenty-one of 29 (724>)) birds
had microscopic lesions consistent with mycobacteriosis.
Lesions were common in the liver, spleen. lung. kidney,
intestines, ovary and bone marrow (Figure 2).
Microscopic lesions of the liver could he divided into
two forms that corresponded to the observed gross
lesions. The first was a severe granulomatous inflamma-
tion characterized by nodules of variable size. They were
composed mainly of histioeytes, lymphocytes and multi-
nucleated giant cells, sometimes with small numbers of
plasmacytes (Figure le). These granulomas rarely con-
tained a central zone of necrosis, except for two birds
and, in some cases, a thin fibrous capsule surrounded the
largest nodules. These nodules tended to be periportal.
but also widely scattered in some birds. Many to massive
numbers of acid-fast organisms were observed. They
were restricted to the central necrotic core of the
granulomas. The second form of microscopic inflamma
tory pattern in the liver was characterized by a severe
diffuse infiltration of the parenchvnia with histiocytes.
scattered multinucleated giant cells and, to a lesser
degree, lymphocytes and plasmacytes (Figure Id). Thick
layers of amyloid were observed between the hepatocytes
and the space of Disse. No or few acid-fast organisms
were associated with this inflammation pattern.
Two similar patterns of inflammation were also
observed in the spleen. The diffuse forni was character-
ized by infiltration of this organ with large numbers of
histiocytes and multinucleated giant cells, with lympho-
cyte and erythrocyte depletion. Caseous necrosis was
observed in the more extensive areas of inflammation.
Many to massive numbers of acid-fast organisms were
observed in these lesions. The second pattern consisted
of mild focal or multilocal histioeytic nodules, in some
cases accompanied by multinucleated giant cells. Central
necrosis was not common in these birds. No or few acid-
fast organisms were observed in this form of inflamma-
Focal or multi-focal granulomatous pneumonia was
observed in seven non-white doves and two white doves,
respectively. Two white doves and two non-white doves
had mild multifocal, lymphocytic nephritis but necrosis
was not a component of the kidney lesions. A severe,
diffuse, air saculitis characterized by large amounts of
necrotic debris, exudate and severe histiocytic infiltration
with massive numbers of acid-fast bacteria was observed
in three non-white birds.
Moderate to severe multifocal scrosal and mucosal
granulomatous enteritis was observed in 13 birds. Mild
multi-focal to severe diffuse hone marrow inflammation
was observed in II non-white doves, characterized by
replacement of normal bone marrow by hystiocytes and
multinucleated giant cells.
Very mild lesions in the liver. spleen or lung, without
detectable mycobacteria in acid-fast stained tissues,
Mycobacteriosis in ring-neck doves 447
0 White?• Non-white?
Figure 2. Higher prevalence of organs affected in non-while diseased ring-neck doves (S. rlsoria compared nob diseased it/tile ring-
neck doves. Lans include air sacs. Averages f). the nwnber of organs affected /r the dif.fr rent colour morphs were statistically significant.
as stated in Table 1.
smears, cultures and PCR, were observed in three white
birds and one non-white bird.
Results of culture and PCR. Overall, 18 out of 29 (62%)
birds were considered infected, based on positive results
from cultures and PCR and/or by the detection of acid-
fast bacilli in one or more tissues or smears (Table 1). An
amplicon of cxpccied molecular mass (236 base pairs)
was amplified by PCR from the liver or spleen from four
white and six non-white doves. These sequences were
identical and had 1007 identity with the sequevars of Al.
at'iwn subsp. aria/n that contains serotypes 2, 3, 4 and 9
(Morita ci ai., 2004).
Health and infection status. Based on the presence of
gross and microscopic lesions, 21 of 29 (724%) birds
were considered diseased. Seventeen birds were consid-
ered severely diseased while the four birds that had
microscopic lesions but were negative for mycobacteria
were considered mildly diseased. With the exception of
one bird, all of the 18 infected birds showed microscopic
lesions and were considered diseased. This negative dove
was considered infected based on positive culture and
PCR of liver and spleen samples, but classified as healthy
infected in the absence of significant lesions.
Differences between white and non-white coloured doves.
The prevalence of infection in the white doves (36.4%)
was significantly lower than in the non-white morphs
(77.7%). White doves had on average fewer organs
affected than the non-white doves. The pattern of
inflammation was significantly different between the
two groups. The association between diffuse pattern
in the liver and spleen was significantly different between
white and non-white doves (Table 1). This diffuse pattern
of inflammation was rare ill the white doves. No
statistically significant differences in the prevalence of
disease between white doves arid non-white doves were
The present study investigates a natural presentation of
mycobacteriosis in ring-neck doves. Important observa-
tions are the variability observed in susceptibility to
infection, organ distribution and nature of lesions
between white and non-white doves. In the presence of
identical environmental conditions, these differences
may he explained by genetic differences associated with
the phenotypic characteristic colour morph. Previous
findings in another group of ring-neck doves (Saggese &
Phalen, 2005) as well in other species of doves (ll(jlicek
& Trcml, 1993) support it genetic cause for these
differences. While the age and time of infection for
each individual dove was unknown, all were adults kept
under identical food and housing conditions. The
presentation of this disease. constant exposure and the
chronic nature of the lesions of mycohacteriosis together
with the sample size make it unlikely that age or time of
infection influenced our results.
There are several reports of mycobacteriosis in
pigeons and doves (Feldman. 1938: Pond & Rush.
1981: Hejlicek & Treml. 1993, 1995: Morita ci al.,
1994: Bougiouklis ci al., 2005: Saggese & Phalen.
2005), but the prevalence of infection and/or disease in
captive Populations of ring-neck doves have not been
previously reported to the author's knowledge. Overall,
the prevalence of mycobacteriosis in captive collections
of birds is rarely higher than 15% (Montali et al.. 1976:
Vail der Heyden, 1997; Tell ci al., 2001). Nevertheless,
while the prevalence of infection (62%) and disease
(72.4%) was considered very high in this flock, the
finding that not all the birds were infected suggests that
CXOSUC alone under the conditions observed in this
flock (overcrowding, poor hygiene) was apparently not
sufficient to cause infection or or disease in some birds.
The distribution of gross and microscopic lesions in
these birds was similar to that previously reported in
other birds with mycohacteriosis. The liver, spleen, lung.
bone marrow are common sites of mycobacterial infec-
tion in birds (Feldman, 1938; Francis. 1958; Thoen,
1997; Tell ci al., 2001: Fulton & Tlloen, 2003; Converse,
2007). Focal or multi-local granulomatous inflammation
is the most common form observed in this disease
(Montali ci al., 1976: Fulton & Thoen. 2003: Schmidt
ci al., 2003). The diffuse pattern of granulomatous
inflammation observed in this study is consistent with
the non-tuberculoid form described by Tell ci al. (2001),
NI D. S:igg.c CI i/I.
in which diffuse infiltration of the organ with inflam-
matory cells occurs. The diffuse enlargement observed in
12 doves with diffuse histiocytic and multinucleated
giant cells and severe amyloidosis is consistent with
this description. A diffuse form of granulomatous
inflammation similar to that observed in the non-white
doves was previously observed in wild-type ring-neck
doves but not in white birds (Saggese & Phalen, 2005).
This pattern of inflammation resembles the lepromatous
form of granulomatous inflammation observed in hu-
man leprosy (Connor ci til., 1997). The presence of this
diffuse form contrast with reports in other species of
doves, where the tuberculoid or nodular form of
granulomatous inflarmilation has been reported (Feld-
man, 1938: Pond & Rush. 1981; Morita et of., 1994;
Bougiouklis CT al., 2005). Alternatively, it has been stated
that tubercles rarely develop in Columbiformes with
niyeobacteriosis, although specific details were not
provided (Ramis ci al.. 1996). Nevertheless, the presence
of both types of inflammation in the doves of our series
may explain these conflicting opinions.
Twelve birds had amyloidosis of the liver. Massive
amounts of amyloid were observed in doves with diffuse
inflammation, but very little was observed in the birds
with multifocal inflammation. Amyloidosis is a patho-
logical condition characterized by the deposition of
insoluble fibrillar proteins in various tissues and organs
of the body following prolonged inflammation or infec-
tion (Cotran ci al.. 1999). Amyloid deposits have been
reported previously in birds with chronic inflammatory
diseases such as mycobacteriosis and aspergillosis.
Several forms of amyloid have been described in
mammals, but only amyloid AA (amyloid associate)
has been found in birds (Landman ci al.. 1998; Cotran ci
al., 1999: Schmidt ci al., 2003). Amyloid AA is a product
of the proteolytic cleavage of serum AA (SAA), an acute
phase-protein produced by hepatocytes (Landman ci al..
1998). The concentration of SAA in the blood increases
within a several hours of the onset of injury, infection, or
inflammation. Production of SAA is directly stimulated
by the cytokines interleukin- I, interleukin-6 and tumour
necrosis factor-a produced in response to tissue injury
and inflammation (Petersen ci al.. 2004). The persistent
inflammation caused by chronic mycobacteriosis is a
probable cause of the deposition of amyloid in these
organs (Saggese ci al., 2007). Amyloid was not a feature
in the mildly diseased doves with focal or multifocal
granuloniatous inflammation. suggesting that an inflam-
matory process in these birds was insufficient or of too
short duration to trigger amyloidosis, supporting the
suggestion of an infection arrested at early stages.
There were significantly fewer organs with gross and
microscopic lesions in the white doves compared with
other birds. Lung and intestines were rarely affected in
the white doves compared with the non-white doves.
These findings suggest that lesion distribution, as well as
the severity of the lesion and the type of the lesion, are
influenced by factors linked to feather colour.
Four doves had mild lesions consistent with a
mycohacterial infection but were negative oil tests
for the organisms. It is possible that these birds had low
levels of mycobactcria in their tissues and that they were
not detected. However, it is more likely that these birds
had recently overcome a mycobacterial infection through
a mild but adequate cell-mediated immune response. It is
probable that the mild lesions observed in these four
birds represented a controlled or at least an arrested
infection, similar to that seen in other niycobacterial
infections (.Juhh ci al.. 1993; Cotran ci al.. 1999;
Dannemberg, 2006). It suggests that at least some birds
may recover from natural infection. The fact that three
out of these birds were white is consistent with other
observations made between different colour morphs.
A single dove with confirmed m ycobacterial infection
of the liver and spleen did not have lesions. The
significance of this is unknown, but could represent the
early stage of infection that was prior to the onset of
detectable lesions or that a lesion was present but not
detected. This case shows that, in some circumstances.
culture or PCR may be a necessary adjunct to histo-
pathology to detect all infected birds.
The present study represents the first attempt to
examine the association between feather colour and
susceptibility to infection, disease and pathology. The
while doves had it prevalence of infection, fewer
infected organs affected and a different pattern of
inflammation as compared with the coloured doves.
These data are consistent with epideniiological and
genetic studies showing immune response polymorphism
to mycohacterial infections in humans and other mam-
mails (Bellamy. 2005: Dorman ci al.. 2004; Barthel ci al..
2000; Pan ci al., 2005: Di Pietrantonio & Schurr, 2005)
and in different strains of chickens (Hit ci al.. 1997:
Bacon ci al.. 2000). Specific genes that have been
associated with differing immune responses to mycobac-
terial infections include those that code for the major
histocompatahility receptors, cytokines. T-cell receptors.
immunoglobulins and NRAMPI (Zekarias ci al., 2002).
The lack of information available about the role of
genetics and susceptibility to tuberculosis in birds
contrasts to what is known in humans and other
mammals (Bellamy & Hill, 998). Both environmental
and genetic factors and their interaction influence
susceptibility to tuberculosis in humans (Casanova &
Abel. 2002: Schurr. 2007), in laboratory animals such as
rabbits and mice, and in domestic mammals (Barthel ci
al., 2000: Phillips ci al., 2002; Di Pietrantonio & Schurm',
2005: Dannemherg. 2006). For example, in humans
infected with M. tuberculosis, less than I 01X of infections
progress to clinical disease (Cole ci al.. 2004). Resistance
to clinical disease has been linked with ethnic back-
ground and race (Bellamy ci al.. 2000: Lim, 2000;
Casanova & Abel, 2002; Van Helden ci a/.. 2006). Genes
coding for natural-resistance-associated-macrophage-
protein 1 (NRAMP1). vitamin D receptor, interferon-'y
receptor, interleukin- I. interleukin- 10 and interleukin-
12, HLA class 11 molecules, Toll-like receptor 2 and
tumour necrosis factor-. are all considered to influence
immunity to mycobacterial infection. Their deficiency.
functional defect or genetic polymorphism has been
associated with altered susceptibility to mycohacteriosis
(Taflik. 2001: Casanova & Abel. 2002: Phillips ci al..
2002; Acevedo-Whitehouse ci al.. 2005: Bellamy, 2005:
Okada & Shirakawa. 2005; Hill, 2006: Naik, 2006). The
chromosome location of some of these genes has been
elucidated (Cervino ci of., 2002; Bellamy, 2005; Bagh-
dadi ci al., 2006).
Ring-neck doves have been selected for different
phenotypic traits, mainly colour, for more than 2000
years, and more than 45 colour morphs are currently
recognized by pigeon fanciers (Oliver. 2005). The genet-
ics that govern the colouration of ring-neck doves have
Mycobacteriosis in ring-neck doves 449
been partially deduced by Miller (2007). There are three
basic colour morphs in ring-neck doves: dark or wild
type, blond and white. Dark is dominant both over
blond and white, and blond is dominant over white. The
alleles coding for colour are sex-linked, and are located
on the sex (Z) chromosome. Females are single sexual
chromosomed (ZW or Z-) and males are double sexual
chromosomed (ZZ). Females' with a single white gene
and hornozygous males will be white. It is very probable
that the gene or genes involved in immunity to Al. ariuni
subsp. aria/n infection in these doves could be associated
with these loci or at least located in the same (Z)
The present study received generous support from The
Schubot Exotic Bird Health Center. the Association of
Avian \/etetrinarians and the Smokey Mountain Bird
Club. The authors are grateful to Patricia Gray. Darrel
Styles, Elizabeth Tomaszewski and Debra Turner (The
Schuhot Exotic Bird Health Center. College of Veter-
inary Medicine, Texas A&M), and to David McMurray.
Luc Bcrghman, Christine McFarland. Gerald Bratton,
Bob Daihaussen, Lisa Tell, Michael Garner, Allison
Bradley. Jan Suchodolsky, Taflik Omran. Mellisa Libal,
Karen Russell, Y. Ni, Ken Turner, Rosemary Vollmar,
Chantail Mukherjee, Sarah Jones, John Edwards. Bill
Wigle. Gabriel Gomez. George Stoica. S. Vanhooser,
John Roths and student workers at Texas A&M
University for their assistance with different aspects of
Acevcdo-Whitehouse. K., Vicente. J., Gortazar, C Hiifle. LI., Fern.in-
dee-de-Mera. I.G. & Amos. W. (2005). Genetic resistance to bovine
tuberculosis in the Iberian wild boar. :>Io/ecular Ecolog y. 14, 3209
Bacon. L.D. H wit. H.1). & Cheng. 11.11. (2000)..review of the
development of chicken lines to resolse genes determining resistance
to diseases. Po,idrr ,Scic,ii'e. 79. 1082 1093.
Baghdadi .J.F.. Orlova. M., Alter. A., Ranque. B.. Chentoufi, M..
I,azrak. F. Archane, Mi., Casanova, iL.. Benslimane, A.. Schurr. E.
& Abel. L. (2006). An aulosomal dominant major gene confers
predisposition to pulmonary tuberculosis in adults. Journal I
E.vperioieiito/ 3iiluin.. 203. 1679 1684.
Barthel, R., Picdrahita, J.A.. McMurray. D.N.. Payeur. J.. Baea, 0..
Suarez-Guemet. 1-.. Perurnalla, VS., Ficht. l.A.. Templeton. J.W.&
Adams. L.G. (2000). Pathologic findings and association of limo-
bacteriuoi bori,s infection with the bovine N RAMP I gene in cattle
from herds with naturally occurring tuberculosis. ..lou'ru-ii Journal of
I 'ierioar r Research. 61. 1140 1144.
Bellamy, R. (2005). Genetic susceptibility to tuberculosis. C ioiic.v in
(7ie,sr Sieilieiiie. 26, 233 246.
Bellamy. R.. Bcyers. N., McAdam, K.R. Russende. C.. Gie, R., Samaai.
P., Bester. D,. Meyer. M.. Corrah, I., Collin, M.. Camidge. DR.,
Wilkinson. L).. 1-loal-Van 1-lelden, I'... Whittle, I IC.. Amos. w.. Van
Holden, P. & Hill. A.V, (20)10). Genetic susceptibility to tuberculosis
in Africans: a genome-wide scan. Proceedings National . cadenir of
,Sci,ues. t-'S,1. 97. 8005-8009.
Bellam. R.J. & I lill. A.V. (1998). Genetic susceptibility to mycobacteria
and other infectious pathogens in humans. Current Opinions in
ininiwio/ogi. /0. 483 487.
Bertelsen. M.F., GrOndahl. C. & Giese. S.B. (2006). Disseminated
.tlrcobacteriuni ce/ioum infection in a white-tailed trogoil ( Trogon
ririi/i,$). Anon Paiho/ogi. 35. 116 319.
Bougiouklis, P. Brellou, G., Fragkiadaki. E.. lordanidis. P., Vlemmas. 1.
& (ieorgopoulou, I. (2005). Outbreak of avian mycobacteriosis in a
flock of two-year-old domestic pigeons (Colwnha Jima f donie,stiiii).
,-lrian Diseases. 49. 442 445.
Casanova. J.L. & Abel. L (2002). Genetic dissection of immunity to
mycohacteria: the human model. Annual Rerir'ir oflinniullologia, 20.
Cervino, AC., Lakiss. S., Sow, 0., Bellamy, R., Beyers, N.. float van
Helden, E., van Holden, P., McAdam, K.P. & Hill, A.V. (2002). Fine
mapping of a putative tuberculosis-susceptibility locus on chromo-
some 15q]1-13 in African fansilies. /iunian Molecular Genetii:s, Ii,
Cole S. Eiscnach, K.1)., McMurray. C. N. & Jacobs. W.R. Jr. (Eds.)
(2004). Tuhercu/os is and the inhere/c Bacillus. Washington, DC: ASM
Converse, K.A. (2007). Avian tuberculosis. In N.J. Thomas. D.B.
I lunter & C.T. Atkinson (Eds.), infectious Diseases of Wild Birds
(pp. 289 302). Ames. IA: Blackwell Publishing.
Connor. DI-!.. Chandler, F.W.. Schwartz. D.A.. Mane. H.J. & Lack, F.
(Eds.) 119971. Pat/io/ogr of /iifeciioirs Diseases. New York: McGraw-
Cotran. R.S.. Kumar. V. & Collins. T. (1999). Bobbins Pathologic Basis
of Diseases. 6111 cdii (pp. 251 259). Philadelphia. PA: WB Saunders
Cromie. R.L.. Brown, Mi.. Price. D.J. & Stanford, J.L. (1991).
Susceptibility of captive wildfowl to asian tuberculosis: the impor-
tance of genetic and environmental factors. Tuhencle. 72. 105 109.
Cromic, R.L., Brown. M.J. & Stanford, JL. (1992). The epidemiology
of asian tuberculosis in white-w iisged wood duck C airuia nato/ala at
The Wildfowl and Wetland Trust. Slimbridge ('mitre (1976--1991).
I-I i/d/ow/. 43. 211 214.
Cromie, R. L.. Ash, N.J., Brown, Mi. & Stanford. J. 1.. (2000). Avian
immune response to lfj-eobcicreriuni oriuui: the wildfowl example.
Deii'/opineniol and C'oniparotice bnniunologi . 24. 169-185.
Dan nenibcrg. A.M. Jr. (2()()6(. Pathogeni'.ris 0/ Haitian Tuberculosis.
in.sight.s from the Rabbit Model. Washington. DC: ASM Press.
Di Pietrantonio. T. & Schurr. E. (2005). Mouse models for the genetic
studs of tuberculosis susceptibility. Briefoig .s in Fiini-iiooa/ (,eiiooius
and Proteo,nis. 4, 277 292.
Dornian, S.F., Hatem, CL., Tyagi, S.. Aird. K.. Lopez-Molina. J,. Pitt.
ML.. look. B.C.. Dannenherg, AM.. Bishai. W.R. & Manahe. Y.C.
(2004). Susceptibility to tuberculosis: clues from studies with inbred
and outhred New Zealand White rabbits. Infecti on and Ioiniunitr. 72,
Feldman. 'A'. H. (1938). Arian Tuberculosis infections. Baltimore, MD:
Williams and Wilkins.
Francis J. )1858). Tuberculosis in ,411oials and Ma,i. A Stud y on
('aui/ia/atii'i' Pioliologr. London: Cassell Press.
Friend, NI. (2(1(11). Asian tuberculosis. In M. Friend & J.C. I- ranson
(Eds.), Field .t/wii,al of i-I ildilfi' Diseases (pp. 93 98). Madison. WI:
US Geological Survey. Biological Resources Division. National
Wildlife Health Ccc tci.
Fulton. R.M. & Thoen. ('.0. (2003). Tuberculosis. In R.W. Calnek.
II.H. Baines. C.W. Beard, L.R. McDougald. Y.M. Sail (Eds(.
Diseases of Pou/tnr (pp. 1136 844). Ames: Iowa State Press.
Gross. WB.. lalkinlsam, J.D. & Payeui'. J.B. (1989). Effect of
environmental genetic interactions on Mrcobacteriwn aniwn chal-
lenge infection. .4vian Diseases. 33, 411-415.
Hejlicck. K. & Treml. F. (1993). Epizootiology and pathogenesis of
avian mycobacteriosis in doves (Streptopelia sp.). 14'terniart' Medi-
cine (Praha). 38. 119-328.
Hejlleek. K. & Treml. F. (1995). Comparison of the pathogenesis and
epizootiologic importance of avian mycohacteriosis in various types
of domestic and free-living syntropic birds. Vi'terinarr Medicine
(Praha), 40. 187-194.
Hill. A.V.S, (2006). Aspect of genetic susceptibility to human infectious
diseases. Annual Rei'icir.s in Genetics, 40. 469-486.
Hoop. R.K.. Bottger. E.C. & Pfyffer. G.E. (1996). Etiological agents of
mycohacteriosis in pet birds between 1986 and 1995. Journal of
Clinical Microbiology../4. 991 992.
Hu. J.. Bumstead. N.. Barrow, P., Sehastiani, G.. Olien. L.. Morgan. K.
& Malo, D. (1997). Resistance to salmonellosis in the chicken is
linked to NRAMPI and TNC. Geoonie Research, 7. 693- 704.
45)) M. D. Saggese ci al.
Jubh. K.V.F.. Kennedy. P.C. & Palmer. N. (1993). Pathologr of Doniestic
Aniiiials, Vol. 1. 4th edn. New York: Wil Saunders Co.
Landman, W.J.M.. Gruys. F. & Gielkens. A.L.J. (1998). Avian
amyloidosis. Aiim' Pathology, 27, 437-449.
Lim. T.K. (2000). Human genetic susceptibility to tuberculosis. Annals
.4cadenii of Mcilicii,e of Si,i'apore, 29, 298 304.
Mahon, CR., Maiiciselis. G. & Lehman, D.C. (2007). Textbook of
Diaipto.ciic it(icrobiologi New York- U. WB Saunders Co.
Miller. W.J. (2007). Genotypes and description of ritigneck plumage
colors and eye cover. Available online at http:/Iwww.ringncckdove.
com Accessed November 25 2007.
Montali. Ri.. Bush, M., Thoen. CO. & Smith. E. (1976). Tuberculosis
in captive exotic birds. Journal of the ,'lmerican Veterinarian Medical
Association. 169, 920 927.
Morita, Y., Arai, M., Nomura. 0., Maruyama. S. & Katsube. Y. (1994).
Avian tuberculosis which occurred in air pigeon and
pathogenicity of the isolate,. Journal of Veterutarr Medical Sciences,
56. 585 587.
Morita, Y., Maruyama, S.. Kabeya. H.. Nagai, A.. Kozawa. K.. Kato.
M.. Nakajima. T.. Mikami. T., Katsuhe, Y. & Kimura. H. (2004).
Genetic diversity of the dnaJ gene in the All'c-ohaeteriusn anon,
complex. Journal of Medical Microbiology. 53. 813- -817.
Naik. S. (2006). Carl
look forward to genetic tests for tuberculosis
susceptibility and severity? Indian Journal of .t.Ic'diccd Research, 124,
Okada. M. & Shirakawa, T. (2005). Frontier of mycobacterium
research-gost vs. mycobacterium. Kekkakcc. 80, 613 629.
Oliver. K.\V. (2005). Ringstc'ck Dc,re.c.' A Handbook of Care and Breeding.
Newports News. VA: Author's edition.
Pan. H.. Yan. B.S., Rojas. M., Shebzukhov. Y.V. Zhou. F-I., Kohzik, L..
Higgins, D.E., Daly, Ml.. Bloom. B.R. & Kramnik. 1. (2005). Iprl
gene mediates innate immunity to tuberculosis. ,'Vcctcct'c'. 434. 767-772.
Petersen, HI-I.. Nielsen, J.P. & Heegaard. M.H. (2004). Application of
acute phase protein measurements in veterinar y clinical chemistry.
I i'terinarn Research, 35, 163-187.
Phillips. Ci., Foster. CR., Morris. P.A. & Teverson. R. (2002). Genetic
and management factors that influence the susceptibility of cattle to
Mic-obacieriuni hoii.s infection. Animal health Research Rc'c'u'cc', 3. I
Pollock. C.G. (2006). Implications of mycobacteria in clinical disorders.
In G.J. Harrison & T.L. Lightfoot (Eds.). Clinical Arian Mecficine ( pp.
681-688). Palm Beach, FL: Spix Publishing.
Pond. C.L. & Rush, H.G. (1981). Infection of white earneaux pigeons
Cohinibia /ii'ia) with ,i'Ii'cohcicteriunt at/mu. Laharatorr Animals
Science. 31. 196 199.
Raniis. A.. Ferrer, L., Aranaz. A., Lilbana. F., Mateos, A., Dominguez.
L., Pascual, C.. Fernandez-Garayazahal. J. & Collins. M.D. (1996).
Mucschactericcni genccrensc' infection in canaries. Arian Drseasc'r. 40,
Saggese. NI. I). & Phalen. D.N. (2005). Serological and histological
findings in doses with mycobacteriosis. In I'roc-c'ecicu,g.s of clii' 26"
A.s.socicclioci of .4c'ian 14'ter/naricimc,v
Conference ( pp. 71 73). Monterey.
Saggese. M.D., Riggs. G.. Tizard, I., Bratton. G.. Taylor. R. & Phalen,
D.N. (2007). Gross and microscopic findings and investigation of the
aethiopathogenesis of' mycohacteriosis in a captm\e popumlation ot
white-winged ducks ) Cairina .ccic(ic/atci ). Arian Pccchicclicgi. 36, 415
Schmidt. RE.. Recti-ill. D.R. & Phalen ., D. (2003). Pctticoloc,'v of i',! and
4,/arc Birds. Ames, IA: Blackwell Publishing.
Schuri'. F. (2007). Is susceptibility to tuberculosis acquired or inherited?
Journal ol lucternccl ,t.Ic'di,'ini'. 261. 106 111.
Steinmetz, H.W,, Rutz. C., Hoop. R.K., Grest. P. Blev. C.R. & Halt.
J. NI. (2006). Possible Ii uman-avian transmission of ,ti,'cohoeterimini
tmcherculo,sis in a green-winged macaw (Ara chcloroptc'ra). ,'Inion
Diseases, 50. 641 645.
Taffik . H. (2001). The role of' human genetic factors in susceptibility to
tuberculosis. Aria ('iendftccc I i'nc'olano. 52) Suppl 1). lb 18.
Tell, L.. Woods. L. & Cronuie. R.L. (2001). Mycobactercosis in birds.
Revue Sc-is'uit/ficice c-i 'Ii'chnique, 0/fcc-c-' It, iecscccocsnccl des Epc:ootces. /
Tell. I.., Woods. L.. Foley. i.. Needham. M.L. & Walker, RI. (2003). A
model of avian mycobacteriosis: clinical and histopathologic findings
in Japanese quail ( Cocccr,ci v coicc,'ciix japcctciea ) intravenously inocu-
lated with Mc'eobicccc'ricsnt ariiuhc Am' ian I)csc'ic.,e.,', 47. 433 443.
Thoen. CO. (1997). Tuberculosis. in B.W. C'alnek (Ed.). Diseases of
Poultry 10th edn. Ames: Iowa State Universit y Press.
Thompson, J.L).. Gibson. T. Plewniak, iF.....,cnmougin. I-. & Higgins.
D.G. (1997). The CLLISTAI, X windows interface: flexible strategies
'or multiple sequence alignment aided by quality analysis tools.
!Vui-lew .'tc'lsl Resc'arch, 25, 4876 4882.
Travis. E.K.. Jtinge, R.E. & Terrel, S.P. (2007). Infection with
thc-c-obat-ceriucn sinciae complex in ('our captive Micronesian king-
fishers. Jocmrcucf .cuier0 an I 'c'tc'riuiari' Jhi'chc'c'ccl Assoeiat cccii. 230. 1524
Van der l-Ieydcn. N. (1997) Clinical manifestations of mycohacteriosis
in per birds. ,Se,uuciccrs hi -I i'icccc and E.vcciie Pc't,s Mechcuie, 6, IS- 24.
Van der Schaaf, tV. Hopmans..l.I.. & Van Beck. J. (1976). Mycohacter-
ial intestinal disease in woodpigeons (Columbia palunihus). T,fdsc'hr
D/c'cgc'nec'.skd, 101. 1)11(4 1092.
Van Heiden. PD., Moller. M., Babh, C... Warren. R., WaIzI, G.. U ys. P.
& 1-loal. E. (2006). Tuberculosis epidemiology and human genetics.
,-Vorarit.v Fomc,idcctjoic .S'i',mcpo.siicucm. 2 79. 17 -31
Zekarias. B., Ter Hurne. A.A.. Landman. WI Rebel. J.M.. Pol. J.M. &
Grays. E. (2002). Immunological basis of differences in disease
resistance in the chicken. I 'oter,ciarr Rc'.c'eorc'hi .33, 109-125.