Parasitol Res (2006) 98: 576–581
O. Cordova Paz Soldan
F. Vargas Vásquez
A. Gonzalez Varas
G. Peréz Cordón
J. R. Velasco Soto
I. Rodríguez Gonzalez
M. J. Rosales Lombardo
Intestinal parasitism in Peruvian children and molecular
Received: 27 September 2005 / Accepted: 8 December 2005 / Published online: 24 January 2006
# Springer-Verlag 2006
Abstract Intestinal parasitism was studied in children of
Trujillo (Peru) to create a prevention and control program.
Fecal samples of 489 children were examined. The general
prevalence of intestinal parasitosis was found to be 68%.
The most frequent pathogenic enteroparasites were Giardia
lamblia (26.4%), Cyclospora cayetanensis (13%), Hyme-
nolepis nana (2%), Hymenolepis diminuta (1.6%), and
Cryptosporidium spp. (1%). All these parasites appeared
both in diarrheic and nondiarrheic children, except Cryp-
tosporidium, which invariably caused diarrhea. Multiple
parasitism was frequent, 45.6% of the children presenting
two, three, or four intestinal parasites. Cryptosporidium was
the only parasite that was not associated with the others.
Only five children were affected of cryptosporidiosis, pre-
senting explosive diarrhea, nausea, and vomiting. Crypto-
sporidium species and genotypes involved in the infantile
cryptosporidiosis were determined by polymerase chain
reaction-restriction fragment length polymorphism. Four
children were parasitized by Cryptosporidium hominis and
only one by Cryptosporidium parvum. Our results confirm
that anthroponotic transmission of Cryptosporidium is
predominant in Peru.
Intestinal parasitism among children can be considered in-
dicative of the socioeconomic status and sanitation levels
of a population. The prevalence of enteroparasitoses is
linked to both poor hygiene and inadequate sources of
drinking water. In children, intestinal parasites are as-
sociated with deficient growth, impaired cognition, and
death (WHO 1996). In San Juan de Miraflores, Peru,
Berkman et al. (2002) studied the way in which stunted
growth, diarrhea, and parasitic infection during infancy
affect cognition in late childhood. This work showed par-
asitic infection and stunting during infancy having a strong
adverse effect on cognitive function in late childhood as-
sociated with reduction in IQ scores after adjustment for
socioeconomic, schooling, and other significant factors.
Therefore, the establishment of prevention programs,
control, and treatment of intestinal parasites is fundamental
in developing countries. In Peru, infections from intestinal
parasites are frequent in children. Previous epidemiological
surveys conducted in Trujillo established a prevalence of
30% for Giardia in children under 10 years of age with
acute diarrhea (Vargas et al. 1987). In Puno (Maco et al.
2002), intestinal parasitosis was found to be 91.2%.
Cryptosporidium was first studied in Peru by Soave and
Armstrong (1986), reporting 8.1% prevalence in Lima,
using a total of 111 diarrheic stool samples. Chang (1987)
described a case associated with acute diarrhea in
Oxapampa, while Huaynalaya et al. (1988) detected the
parasite in a female child in Esperanza. Black et al. (1989),
having analyzed fecal samples from 153 children in a
community near Lima, included Cryptosporidium among
the agents causing diarrhea. Sarabia-Arce et al. (1990)
determined cryptosporidiosis in 10% (24 of 248) of the
children admitted to the rehydration ward at Cayetano
Heredia University Hospital, Lima. These researchers
stated that, in children hospitalized for diarrhea, Crypto-
sporidium parvum occurs more frequently in malnourished
subjects. In Sterling et al. (1991), reported a study of 211
Peruvian children and their mothers comparing antibody
titers in mother’s milk and incidence of cryptosporidiosis.
There was no significant difference in the incidence (0.17,
0.19, and 0.38, respectively) or duration of infection among
children regardless of the level of maternal antibodies.
According to Berkman et al. (2002), Giardia intestinalis
incidence in Lima ranged from 0 to 4.8 episodes per year
O. Cordova Paz Soldan
F. Vargas Vásquez
A. Gonzalez Varas
I. Rodríguez Gonzalez
Departamento de Microbiología y Parasitología,
Universidad Nacional de Trujillo,
G. Peréz Cordón
J. R. Velasco Soto
I. Rodríguez Gonzalez
M. J. Rosales Lombardo (*)
Instituto de Biotecnología, Departamento de Parasitología,
Facultad de Ciencias, Universidad de Granada,
18071 Granada, Spain
during infancy, 86% of children having at least one G.
intestinalis episode during the first 2 years of life. The C.
parvum incidence ranged from 0.56 to 0.61, with 3% of
stool samples testing positive for C. parvum. Cryptospo-
ridium isolated from different regions have different anti-
gens, virulence, infectivity, and sensitivity to drugs and
disinfectants (Fayer and Ungar 1986; Fayer et al. 2000).
Therefore, for the design of control programs, it is vital to
know the species and genotypes of Cryptosporidium in
Two distinct C. parvum genotypes, genotype 1 (anthro-
ponotic genotype) and genotype 2 (zoonotic genotype),
have been recognized for some time to be responsible for
human cryptosporidiosis. However, such species as Cryp-
tosporidium felis and Cryptosporidium meleagridis, Cryp-
tosporidium muris, and a dog genotype of C. parvum are
also considered responsible for human cryptosporidiosis
(Xiao et al. 2001; Palmer et al. 2003). Recently, Morgan
et al. (2002) proposed a new species, Cryptosporidium
hominis, to denote the human genotype. In Lima, C.
hominis has been the most frequently detected species
(Xiao et al. 2001; Cama et al. 2003).
The Spanish Agency for International Cooperation
(Agencia Española de Cooperación Internacional) and the
regional Agencia Andaluza de Cooperación Internacional
have since January 2004 been financing a project of pre-
vention, control, and treatment of intestinal parasites in
Trujillo, to lower the prevalence of parasitic infections
For this, it is essential to study the prevalence of in-
testinal parasites as well as the molecular epidemiology of
some of these pathogens. Therefore, in the present work,
we have analyzed the most frequent types of intestinal
parasitism in children from three districts of Trujillo (Peru)
as well as the species and genotypes of Cryptosporidium
involved in infantile cryptosporidiosis, one of the gravest
afflictions in undernourished children in developing coun-
tries (Fayer et al. 2000).
Materials and methods
Study site and sampling
Trujillo (Peru), capital of the department Libertad, has
more than one million inhabitants, concentrated in city
center with marginal populations on the periphery lacking a
Temperatures are constant throughout the year, at about
22°C, and relative humidity stays at roughly 70%, being
close to the Pacific Ocean. Rainfall is sparse and restricted
The present study on intestinal parasites in children was
conducted in three rural districts on the periphery of the city
of Trujillo: El Porvenir, Buenos Aires, and La Esperanza,
with very low socioeconomic and sanitary levels. El
Porvenir has 18,757 inhabitants, Buenos Aires 8,656, and
La Esperanza 12,404. The three districts have similar living
conditions, in that not all the dwellings have running water,
and thus, inhabitants get water from public fountains or
water trucks, and most of the houses lack toilets.
Prior to the sampling, the sanitation staff of the health
center in each district called a meeting where the study
methods were verbally explained to the parents of the chil-
dren to be studied. A questionnaire was administered to the
parents to return with a fecal sample. The questionnaire
asked the age of the child, the disease, and details on the
diarrhea and its symptoms. After the fecal samples were
turned in, the children were weighed and measured to
complete the questionnaire.
From January to December 2004, stool samples were
collected from children between 1 month and 9 years old to
study intestinal parasites in the schools of each district.
Samples were transported to the laboratory and preserved
in potassium dichromate at 2.5% and kept at 4°C until
macroscopically and microscopically examined. Macro-
scopic inspection determined the consistency and mucosity
as well as the blood and fat contents of the samples. After
examination under a binocular microscope, and afterward a
light microscope, using lugol in some cases, samples were
stained with Ziehl-Neelsen, Giemsa, and Heidenheim and
analyzed by the Kato–Katz method for nematode ova
(WHO 1991). Positive fecal samples for Cryptosporidium
were processed to purify the oocysts by potassium bromide
discontinuous gradient (Entrala et al. 2000). The Teleman
concentration was used when other parasites were detected.
Data were compared between diarrheic and nondiarrheic
children using χ
test. Prevalence of intestinal parasites
was studied having a P value <0.02.
Molecular characterization of Cryptosporidium
species and genotypes
All the positive fecal samples for Cryptosporidium were
processed for DNA extraction. Briefly, 200 μl of fecal
sample in water was suspended in 200 μl of lysis buffer
supplied in the QIAamp DNA mini kit (QIAGEN, USA).
Oocysts were digested using the technique of Robertson et
al. (1993). Genomic DNA was isolated by a QIAamp DNA
stool mini-kit protocol (QIAGEN) directly from the fecal
sample (200 μl/sample). DNA samples were stored at
−20°C until further use.
Polymerase chain reaction-restriction fragment length
Cryptosporidium species and genotypes were determined
by nested polymerase chain reaction (PCR) of an SSU
rRNA gene fragment and restriction fragment length
polymorphism (RFLP) analysis as previously described
(Xiao et al. 1999a,b) but using the endonucleases SspI and
For the primary PCR step, a PCR product about 1,325 bp
long was amplified by using primers 5′-TTCTAGAGC
TAATACATGCG-3′ and 5′-CCCATTTCCTTCGAAACA
GGA-3′ (Invitrogen, Spain). Each PCR mixture (total
volume, 50 μl) contained 5 μl of 10× PCR buffer (BioRad,
Spain), 6 mM MgCl
, each deoxynucleoside triphosphate
at a concentration of 200 μM (BioRad), each primer at a
concentration of 100 nM, 1.5 U of Taq polymerase
(BioRad, Spain), 0.5 μl of DNA template, and 0.1 μg/μl
of bovine serum albumin (BSA; BioRad). Each PCR was
performed in a thermocycler (MyCycler, BioRad), under
the conditions described by Xiao et al. (1999a,b). For the
secondary PCR step, a PCR product 819–837 bp long
(depending on the species) was amplified by using 0.5 μlof
the primary PCR product and primers 5′-GGAAGGGTTG
TATTTATTAGATAAAG-3′ and 5′-AAGGAGTAAGGAA
CAACCTCCA-3′ (Invitrogen). The PCR mixture and cy-
cling conditions were identical to the conditions used for
the primary PCR step, except that 3 mM MgCl
in the PCR and BSA was not added.
For the restriction fragment analysis, an aliquot of 20 μl
secondary PCR products was digested in a 50-μl reaction
mixture containing 20 U of SspI (Sigma, Spain) for species
diagnosis, or 20 U of VspI (Sigma, Spain) for genotyping of
C. parvum, and 5 μl of the appropriate restriction buffer at
37°C for 1 h, under conditions recommended by the
As a positive control, a sample of C. parvum genotype 2
was used from cattle belonging to Granja Puleva, Granada
(Spain). The PCR products and a ladder of 1,000 bp
(Sigma, USA) were electrophoresed in a 2.0% agarose gel
and visualized by ethidium bromide staining.
A total of 489 fecal samples were collected and analyzed:
225 from El Porvenir elementary school (which had 550
students), 178 from La Esperanza (which had 500 stu-
dents), and 86 from Buenos Aires (which had 100 stu-
dents). The median age of the children was 5.3 years
(interquartile range=4.1). One or more intestinal parasitic
infections were identified in 333 (68%) of the children, 152
(45.6%) of them having multiple parasitic infection by two,
three, or four parasites. The protozoa detected (Table 1)
were Giardia lamblia, Entamoeba coli, Cyclospora
cayetanensis, Iodamoeba buschlii, Endolimax nana, Chi-
lomastix mesnili, and Cryptosporidium spp. Blastocystis
hominis was frequent. The helminths were Hymenolepis
nana and Hymenolepis diminuta. In the three districts
studied, the parasite prevalence proved similar: 26.4% G.
lamblia, 13% C. cayetanensis,2%H. nana, 1.6% H.
diminuta, and 1% Cryptosporidium spp.
Of the 489 children sampled, 147 had diarrhea (defined
as a change in the normal pattern of bowel movements,
with at least three loose stools daily).
Table 1 shows the general prevalence of each parasite
and the prevalence for both populations, children with and
without diarrhea. Of all the intestinal parasites found in the
fecal samples, only Cryptosporidium appeared exclusively
in diarrheic children. In the case of G. lamblia, a slight
123 4 5 6 7
Fig. 1 Molecular diagnosis of Cryptosporidium spp. by a nested
polymerase chain reaction-restriction fragment length polymor-
phism (PCR-RFLP) based on SSU rRNA gene sequences, using
SspI in the digestion. Lane 1, molecular weight marker (1,000 bp);
lanes 2–6, Cryptosporidium parvum from children; lane 7, C.
parvum from bovine control
Table 1 Prevalence of intestinal
parasites in children of Trujillo
Parasite Diarrheic children, n (%) Nondiarrheic children, n (%) Prevalence (%)
Giardia lamblia 50 (34) 79 (23) 26.4
Blastocystis hominis 35 (23.8) 83 (24.2) 24.1
Entamoeba coli 19 (12.9) 91 (26.6) 22.4
Cyclospora cayetanensis 21 (14.3) 47 (13.7) 13.0
Iodamoeba buschlii 7 (4.8) 43 (12.5) 10.2
Endolimax nana 8 (5.4) 12 (3.5) 4
Hymenolepis nana 3 (2) 7 (2) 2
Chilomastix mesnili 4 (2.7) 5 (1.5) 1.8
Hymenolepis diminuta 1 (0.7) 7 (2) 1.6
Cryptosporidium 5 (3.4) 0 1
difference is also appreciable between the diarrheic
children (34%) and nondiarrheic ones (23%).
Multiple parasitic infections were common, with 333
presenting intestinal parasitosis, 152 (45.6%) of these with
two, three, or four intestinal parasites. The most frequent
cases of multiple parasitism were G. lamblia and B.
hominis, with a frequent association of the two pathogens,
G. lamblia and C. cayetanensis. All the fecal samples in
which these latter two species appeared in association
belonged to children affected by acute diarrhea with nausea
Cryptosporidium was not associated with other parasites
in any of the five cases diagnosed.
Molecular characterization of Cryptosporidium spp.
Of the 489 children analyzed, only 5 presented Crypto-
sporidium spp., and all had acute diarrhea. Species diag-
nosis was made by digesting the secondary PCR product of
831–837 bp with SspI. All the samples generated three
visible bands of 448, 247, and 106 bp (Fig. 1). For C.
parvum to be differentiated from C. hominis, the secondary
PCR product was digested with Vsp I. C. parvum (C.
parvum bovine genotype) produced a visible band of
628 bp, while the human genotype, C. hominis, produced a
band of 556 bp (Fig. 2). Thus, it could be clearly
distinguished that four children had been parasitized by
C. hominis and only one by C. parvum (the latter being
indistinguishable from the control isolate from Granada,
Spain), which was the bovine genotype of C. parvum.
This study determines the intestinal parasites that affect
children from three districts of Trujillo (Peru) as well as the
Cryptosporidium species and genotypes responsible for
infantile cryptosporidiosis, one of the gravest afflictions in
malnourished children in developing countries (Fayer et al.
The prevalence of intestinal parasites in children in this
study was very high (68%) though lower than the 91.2%
found in another study in Puno, Peru (Maco et al. 2002).
The prevalence of pathogenic enteroparasites was also
different. The Puno study reported 6.6% H. nana, 5.5%
Entamoeba histolytica , 3.3% G. lamblia, 2.2% Taenia sp.,
2.2% Ascaris lumbricoides, 1.1% Trichuris trichura, and
1.1% Enterobius vermicularis. Our study found 26.4% G.
lamblia, 13% C. cayetanensis,4%H. nana, 1.6% H.
diminuta, and 1% Cryptosporidium spp. Low intestinal
cestodosis was found possibly because the basic foods of
these children are vegetables and carbohydrates, while
meat, scarcely eaten, is chicken, the cheapest and ap-
parently the only animal consumed in these communities.
The high prevalence of G. lamblia (26.4%) was striking,
this continuing to register one of the highest infection rates
among children in Trujillo since 1987 (Vargas et al. 1987).
C. cayetanensis had the second highest prevalence, at 13%,
this being very high with respect to previous studies in
Lima (Ortega et al. 1994) or Pampas (Madico et al. 1997),
where prevalence among children was 6 and 1%, respec-
tively. Cryptosporidium spp. were detected in 13.3% of
HIV-positive patients in Lima (Cama et al. 2003) and 11%
in diarrheic children in Pampas de San Juan de Miraflores
(Xiao et al. 2001). In our study, only five cases (1%) were
diagnosed, all in diarrheic children. By contrast, such
enteropathogens as G. lamblia, C. cayetanensis, H. nana,
and H. diminuta appeared in diarrheic and nondiarrheic
children (Table 1) with similar prevalence. It has been
demonstrated that the Giardia cysts isolated from the feces
1234 5 67
Fig. 2 Genotype diagnosis of Cryptosporidium by a nested PCR-
RFLP based on SSU rRNA gene sequences, using VspI in the
digestion. Lane 1, molecular weight marker (1,000 bp); lanes 2–4
human genotype of C. parvum (Cryptosporidium hominis) from
children; lane 5, bovine genotype of C. parvum from a child; lane 6,
bovine genotype of C. parvum from bovine control
The most frequent multiple infections by intestinal
parasites in children of Trujillo (Peru)
No. of cases
G. lamblia + B.hominis 17
E. coli + B. hominis 11
E. coli + G. lamblia 11
G. lamblia + C. cayetanensis 9
E. coli + C. cayetanensis 6
C. cayetanensis + B. hominis 5
B. hominis + I. buschlii 4
E. coli + B. hominis + G.lamblia 7
E. coli + B. hominis + I. buschlii 6
E. coli + C. cayetanensis + I. buschlii 6
E. coli + C. cayetanensis + B. hominis 6
I. buschlii + G. lamblia + B. hominis 6
G. lamblia + C. cayetanensis + B. hominis 4
E. coli + E.nana + B. hominis + I. buschlii 2
E. coli + B. hominis + G. lamblia + I. buschlii 2
E. coli + G. lamblia + C. cayetanensis + I. buschlii 2
of asymptomatic children and used to infect gerbils were
more infective than those from symptomatic children
(Astiazaran et al. 2000). Our results underscore the im-
portance of asymptomatic children as carriers in commu-
nities with poor hygiene where there is poor control over
water or food.
Multiple parasitism was frequent, with 45.6% of the
parasitized children presenting two, three, or four parasites.
Notably, in nine cases, G. lamblia and C. cayetanensis were
associated; in four cases, these two were associated with B.
hominis; and in two cases, G. lamblia, C. cayetanensis , E.
coli, and I. buschlii were all found together (Table 2). In all
cases, the children presented acute diarrhea.
Infantile cryptosporidiosis is especially grave in children
who are immune depressed by malnutrition, as there is
currently no completely effective treatment against Cryp-
tosporidium. Therefore, it is fundamental to establish
prevention and control programs against this parasite. In
this regard, it is essential to know the species and geno-
types of Cryptosporidium in each region, as isolates from
different regions have different antigens, virulence, infec-
tivity, and sensitivity to drugs and disinfectants (Fayer and
Ungar 1986; Fayer et al. 2000).
In the present study, five fecal samples from children
with diarrhea contained Cryptosporidium spp. unasso-
ciated with other parasites. By molecular characterization,
we could clearly distinguish that four children were
parasitized by C. hominis and only one by C. parvum.
These data suggest the possibility of two distinct Crypto-
sporidium populations cycling in children in Trujillo. The
most frequent population appears to involve an anthro-
ponotic transmission cycle, fundamentally in humans. The
other population appears to involve zoonotic transmission
from cattle to humans with subsequent human-to-human
and human-to-cattle transmission. The predominance of C.
hominis in children may be due to the fact that bovine
cryptosporidiosis is low because cattle are not corralled but
rather are pastured in the fields. It is known that the
crowding of the animals in the corrals favors the transmis-
sion of the parasite (Xiao et al. 2004). Similarly, other
studies in Peru have also identified C. hominis as the
predominant species (Xiao et al. 2001; Cama et al. 2003).
Transmission of C. hominis in children can be attributed to
their habit of defecating on the ground in the absence of
toilets in houses and schools and, thus, to contamination of
water and food with human waste.
The present work demonstrates the high prevalence of
intestinal parasites in the infantile population considered.
Based on the results of this study, control and prevention
programs are being started against the most frequent
intestinal parasites, and all the affected children have been
Acknowledgements This work has received financial support from
the Agencia Española de Cooperación Internacional and the Agencia
Andaluza de Cooperación Internacional (AI29/04).
Astiazaran H, Espinosa M, Castanon G, Chavez-Munguia B,
Martinez-Palomo A (2000) Giardia lamblia: effect of infection
with symptomatic and asymptomatic isolates on the growth of
gerbils (Meriones unguiculatus). Exp Parasitol 95:128–135
Berkman DS, Lescano AG, Gilman RH, Lopez LS, Black MM
(2002) Effects of stunting, diarrhoeal disease, and parasitic
infection during infancy on cognition in late childhood: a
follow-up study. Lancet 358:564–571
Black RE, Lopez de Romana G, Brown KH, Bravo N, Bazalar OG,
Kanashiro HC (1989) Incidence and etiology of infantile
diarrhea and major routes of transmission in Huascar, Perú. Am
J Epidemiol 129:785–799
Cama VA, Bern C, Sulaiman IM, Gilman RH, Ticona E, Vivar A,
Hawai V, Vargas D, Zhou L, Xiao L (2003) Cryptosporidium
species and genotypes in HIV-positive patients in Lima, Peru.
J Eukaryot Microbiol 50:531–533
Chang JO (1987) Cryptosporidiosis asociada a diarrea aguda en
Oxapampa, provincia de Oxapampa (Perú). Bol Chil Parasitol
Entrala E, Molina JM, Rosales MJ, Sánchez-Moreno M, Mascaró C
(2000) Cryptosporidium parvum: oocysts purification using
potassium bromide discontinuous gradient. Vet Parasitol
Fayer R, Ungar BLP (1986) Cryptosporidium spp. and cryptospo-
ridiosis. Microbiol Rev 50:458–483
Fayer R, Morgan U, Upton SJ (2000) Epidemiology of Cryptospo-
ridium: transmission, detection and identification. Int J Para-
Huaynalaya E, Miranda H, Mendoza J (1988). Cryptosporidium sp.:
frecuencia en niños con diarrea atendidos en el Centro de Salud
Madre de Cristo del Distrito de la Esperanza, Trujillo.
Resúmenes I Congreso Internacional del Norte de Perú, p 16
Ortega YR, Gilman RH, Sterling C (1994) A new coccidian parasite
(Apicomplexa: Eimeridae) from humans. J Parasitol 80:625–
Maco V, Marcos LA, Terashima A, Samalvides F, Gotuzzo E (2002)
Distribution of entero-parasitic infections in the Peruvian
highland: study carried out in six rural communities of the
department of Puno, Peru. Rev Gastroenterol Peru 22:304–309
Madico G, Mc Donald J, Gilman RH, Cabrera L, Sterling CR (1997)
Epidemiology and treatment of Cyclospora cayetanensis
infection in Peruvian children. Clin Infect Dis 24:977–981
Morgan U, Fall A, Ward LA, Hijjawi N, Sulaiman I, Fayer R,
Thomson RC, Olson M, Lal A, Xiao M (2002) Cryptosporid-
ium hominis n. sp. (Apicomplexa: Cryptosporidiidae) from
Homo sapiens. J Eukaryot Microbiol 49:433–440
Palmer CJ, Xiao L, Terashima A, Guerra H, Gotuzzo E, Saldias G,
Bonilla JA, Zhou, L, Lindquist A, Upton SJ (2003) Crypto-
sporidium muris, a rodent pathogen, recovered from a human in
Peru. Emerg Infect Dis 9:1174–1176
Robertson LJ, Campbell AT, Smith HV (1993) In vitro excystation
of Cryptosporidium parvum. Parasitology 106:13–19
Sarabia-Arce S, Salazar-Lindo E, Gilman RH, Naranjo J, Miranda E
(1990) Case-control study of Cryptosporidium parvum infec-
tion in Peruvian children hospitalized for diarrhea: possible
association with malnutrition and nosocomial infection. Pediatr
Infect Dis J 9:627–631
Soave R, Armstrong D (1986) Cryptosporidium and cryptosporid-
iosis. Rev Infect Dis 8:1012–1023
Sterling CR, Gilman RH, Sinclair NA, Cama V, Castillo R, Diaz F
(1991) The role of breast milk in protecting urban Peruvian
children against cryptosporidiosis. J Protozool 38:23S–25S
Vargas F, Jara C, Castillo R (1987) Protozoarios y helmintos
intestinales en pobladores de Trujillo, Perú. Rebiol 6:3–14
WHO (1991) Basic laboratory methods in medical parasitology.
World Health Organization, Geneva
WHO (1996) Fighting disease, fostering development. World Health
Xiao L, Escalante L, Yang C, Sulaiman I, Escalante A, Montali R,
Fayer R, Altaf A (1999a) Phylogenetic análisis of Cryptospo-
ridium parasites based on the small subunit rRNA gene locus.
Appl Environ Microbiol 65:1578–1583
Xiao L, Morgan U, Limor J, Escalante A, Arrowood M, Shulaw W,
Thompson R, Fayer R, Altaf A (1999b). Genetic diversity
within Cryptosporidium parvum and related Cryptosporidium
species. Appl Environ Microbiol 65:3386–3391
Xiao L, Bern C, Limor J, Sulaiman I, Roberts J, Checkley W,
Cabrera L, Gilman R, Lal A (2001) Identification of 5 types of
Cryptosporidium in children in Lima, Peru. J Infect Dis
Xiao L, Fayer R, Ryan U, Upton S (2004) Cryptosporidium
taxonomy: recent advances and implications for public health.
Clin Microbiol Rev 17:72–97