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■ INTRODUCTION
Tsetse-transmitted trypanosomosis is a serious constraint to live-
stock production and agricultural development in Ethiopia. A total
of 14.8 million cattle, 6.12 million sheep and goats, 1 million
camels and 1.23 million equines are at risk of contracting trypano-
somosis (17). Due to the advancement of tsetse flies into formerly
free areas, an estimated 220,000 km2 zone is presently affected
by tsetse flies (26). These areas are located in the Baro/Akobo,
Omo/Ghibe and Abay/Didessa Valleys along the large rivers of the
country. They have the most arable soils with a high potential for
agricultural development due to high annual rainfall (9). There are
five economically important animal trypanosome species in Ethio-
pia: Trypanosoma congolense, T. vivax, T. brucei brucei, T. evansi
(11) and T. equiperdum (6). The most prevalent trypanosome spe-
cies in tsetse-infested areas of Ethiopia are T. congolense and
T. vivax. Rowlands et al. (29) reported a prevalence of 37% for
■ PATHOLOGIE PARASITAIRE
151
Revue Élev. Méd. vét. Pays trop., 2005, 58 (3) : 151-157
Epidemiology of Bovine
Trypanosomosis in the Abay
(Blue Nile) Basin Areas
of Northwest Ethiopia
Shimelis Dagnachew1 A.K. Sangwan2
Getachew Abebe3*
Summary
The study was conducted between September 2003 and April 2004 in Den-
becha and Jabitehenan weredas (districts) located in the lowland (< 1600 m)
and midland (1600-2000 m) areas. It generated a baseline data on the epide-
miology of trypanosomosis and community awareness regarding the disease in
the Abay (Blue Nile) Basin areas of Northwest Ethiopia. A questionnaire survey
revealed trypanosomosis to be the most important problem affecting animals
and impeding agricultural activities in the areas. Glossina morsitans submor-
sitans was the only tsetse fly species prevalent along with other biting tabanid
and muscid flies. The apparent fly densities (flies/trap/day) were significantly
higher (p < 0.05) in the late rainy season (1.08, 8.78 and 91 for G. m. submor-
sitans, tabanids and muscids, respectively) than in the dry season (0.68, 0.35
and 7.33, respectively). The apparent density of G. m. submorsitans was signifi-
cantly higher (p < 0.05) in the lowland areas than in the midland areas in both
the late rainy season and the dry season. A total of 1648 cattle were examined
for trypanosomosis with the buffy coat technique and the seasonal prevalence
(17.07 and 12.35%, respectively) was significantly (p < 0.05) different. Infec-
tion rates were higher (p < 0.05) in the lowland areas, with 19.87 and 17.62%,
than in the midland areas, with 13.39 and 6.54%, in the late rainy season and
the dry season, respectively. The mean packed cell volume (PCV) values of
parasitemic and aparasitemic animals during the late rainy season were 20.7 ±
3.5 and 26.6 ± 4.3 (p < 0.001), while they were 21.4 ± 3.6 and 26.6 ± 4.3
(p < 0.001) during the dry season, respectively. The regression analysis indi-
cated that the herd average PCV decreased with the increasing prevalence of
trypanosome infections in both seasons.
1. Bahir Dar Veterinary Laboratory, Amhara Region Bureau of Agriculture,
Bahir Dar, Ethiopia
2. Department of Veterinary Parasitology, College of Veterinary Sciences,
CCS Haryana Agricultural University, Hisar125004, India
3. Faculty of Veterinary Medicine, Addis Ababa University, PO Box 34,
Debre Zeit, Ethiopia
* Corresponding author
Tel.: +251 1 33 85 33; fax: +251 1 33 99 33
E-mail: gkibret@yahoo.com (Getachew Abebe)
Keywords
Cattle – Glossina morsitans
submorsitans – Trypanosomosis –
Epidemiology – Site factor – Altitude –
Seasonal variation – Ethiopia.
■ PATHOLOGIE PARASITAIRE
Epidemiology of Bovine Trypanosomosis in Ethiopia
Revue Élev. Méd. vét. Pays trop., 2005, 58 (3) : 151-157
152
T. congolense in cattle in tsetse-infested Southwest Ethiopia. Abebe
and Jobre (1) reported an infection rate of 58.5% for T. congolense,
31.2% for T. vivax and 3.5% for T. brucei in Southwest Ethiopia.
In tsetse infested regions, different workers (2, 24, 34) indicated
a prevalence of 17.2, 21 and 14% bovine trypanosomosis in the
Southern Rift Valley, Metekel district, and Upper Didessa Valley,
respectively, and the dominant species was T. congolense.
Disease surveys are lacking for the Abay Basin areas of Northwest
Ethiopia. The knowledge of insect biology and ecology, and the
status of the disease prevalence are very important for the control
of tsetse transmitted trypanosomosis (12). The aims of the present
study were to determine the seasonal prevalence of trypanosomo-
sis, the apparent density, the distribution and the vector species,
and to assess the community awareness regarding the effects of
trypanosomosis and control methods.
■ MATERIALS AND METHODS
Study areas
The study was conducted in eight peasant associations of Den-
becha and Jabitehenan weredas (districts) of the West Gojjam zone
(10° 30’ N and 37° 29’ E) in Amhara Regional State of Northwest
Ethiopia (Figure 1). The climatic conditions alternate between a
long summer rainfall season (June-September) and a winter dry
season (December-March), with a mean annual rainfall of 1200–
1600 mm. The mean temperature is between 10 and 20°C and the
altitude ranges from 1400 to 2300 m. Temechan and Bir tributar-
ies in the West Gojjam zone join together before entering the main
river (Abay) bordering the study sites. Ponds and marshes were
also found in the lowland areas of the present study. The five dif-
ferent vegetation types, namely savannah, grassland, forest, riv-
erine, and bushland, along with the recently expanded cultivated
lands, are found. These vegetation types are mainly found in areas
below 1700 m, whereas above this altitude the land is occupied by
cultivated lands and small areas are left for grazing purposes.
Study design
The study was based on a questionnaire, and entomological and
parasitological surveys. It was an epidemiological cross-sectional
study covering two weredas in lowland (below 1600 m) and mid-
land (1600–2000 m) areas during the two seasons of the year, i.e.
the late rainy season (just after the main rainy season from Septem-
ber to November) and the dry season (December to March).
Questionnaire survey
To assess the perception of farmers on the occurrence of tsetse and
trypanosomosis, livestock production constraints, socioeconomic
status, herd composition and control methods of trypanosomosis, a
questionnaire survey was undertaken. A total of 80 farmers selected
randomly were interviewed in the study areas.
Entomological survey
The apparent density of tsetse flies and other biting flies in rela-
tion to season, altitude, trap and vegetation types were studied at
selected sites of the areas. The apparent density was determined
based on the mean catches in the traps deployed and expressed as
the number of fly catch per trap per day (14). Entomological data
were collected in both seasons. The flies were caught with mono-
conical, biconical, or NGU traps, baited with acetone and three-
week-old cow urine (4). A total of 142 traps, 70 in the late rainy
season and 72 in the dry season were deployed just before sunrise
and kept in position for 72 h. The species of tsetse flies were iden-
tified based on morphological characteristics (8, 11, 13), and those
of other biting flies according to their morphological characteris-
tics such as size, color, wing venation structure, and proboscis at
the genus level (37).
Parasitological survey
To determine the seasonal prevalence of trypanosomosis and to
assess the risk factors associated with the disease, cattle blood sam-
ples were examined once during both seasons. The study animals
constituted about 600 herds of 30,000 cattle in the study areas.
The sampling strategy was a cluster sampling method (16) and
herds were considered as clusters. The herd (locally called Sheha
or Akata) is defined as a group of cattle owned by people living
together in a village, whose animals share the same barn at night
and the same grazing area and watering points. The sample size
was determined based on the expected prevalence rate of 20% and
absolute desired precision of 4% at confidence level of 95%. So the
optimum sample size for this study was about 800, and 814 samples
from 19 herds and 834 samples from 18 herds were taken during
the late rainy season and during the dry season, respectively.
Blood samples were obtained from the ear vein of each animal
using two hematocrit capillary tubes. They were examined for the
presence of trypanosomes by the dark ground buffy coat technique
(21, 27) and anemia was estimated by the packed cell volume
(PCV) (38). Confirmation of trypanosome species was done using
morphological characteristics (20). During sampling, age, sex, herd
number and altitude of the settlement were recorded. The age was
categorized into three groups (< 1 year, 1-3 years and > 3 years).
Data analysis
Stata version 7.0 software was used for the analysis and interpreta-
tion of the data (33). The apparent fly catches in relation to variables
measured (season, altitude level, vegetation and trap types) were
analyzed using the Kruskal-Wallis test. The prevalence of trypano-
somosis in different variables (altitude level, season, sex and age)
was compared with the chi2-test. A multivariate computation was
conducted by a logistic regression analysis in order to establish the
effects of different risk factors (age, sex, altitude and season) com-
pared with the odds ratio. Student’s t-test and ANOVA were used to
compare the mean PCVs of parasitemic and aparasitemic animals,
and the effect of altitude on PCV values in both seasons. The rela-
tionship between herd prevalence of trypanosome infections and
herd average PCV was examined by a regression analysis using
Figure 1: Map of Ethiopia and the study districts (Denbecha
and Jabitehenan).
Epidémiologie de la trypanosomose bovine en Ethiopie
153
Revue Élev. Méd. vét. Pays trop., 2005, 58 (3) : 151-157
the herd average PCV as the dependent variable, and the prevalence
of trypanosome infections in a herd as the independent variable.
■ RESULTS
Questionnaire survey
Twenty percent of the respondents settled in the areas during the
1940s, 40% during the 1960s, 20% during the 1970s, 15% during
the 1980s and 5% during the 1990s. The farmers still continue to
settle in the lowland areas from the highland weredas of the West
Gojjam zone and from the same wereda also. Respondents’ liveli-
hood was predominantly (97%) based on mixed crop livestock pro-
duction systems. The average cultivated land and cattle holding per
household were about three hectares and three cattle. The composi-
tion of livestock species in the lowland for cattle, small ruminants
and equines was 75, 15 and 10%, while in the midland it was 60,
35 and 5%, respectively. The average cattle herd size was 43 and
each herd included cattle from several owners (seven on average).
The main livestock constraints as perceived by the respondents
were livestock diseases, lack of grazing land and watering points,
and scarcity of modern veterinary services. The main livestock dis-
eases in order of importance were trypanosomosis, anthrax, pas-
teurellosis, blackleg, contagious bovine pleuropneumonia, internal
parasites and external parasites.
According to 95% of the respondents, trypanosomosis (local name
Mich or Ghendi) turned out to be the main problem affecting livestock
productivity and agricultural activities. Almost all the respondents
considered trypanosomosis as a disease of cattle mainly, followed by
equines and small ruminants. The clinical signs of trypanosomosis, as
known by the interviewed people, included rough hair coat, diarrhea,
coughing, constipation, emaciation, weakness, reluctance to move,
isolation from the herd, depression, abortion, inappetence, etc. The
impacts of trypanosomosis were described by the respondents in the
following sequence: loss of draft power, under cultivation, abortion,
reduced fertility, cost of treatment, mortality, loss of milk and meat
production, etc. With regard to the knowledge on transmission of
trypanosomosis, 80% of the respondents indicated that the transmitter
(vector) and cause of the disease were the environment, 15% believed
that biting flies, locally called Lesso and Wegie (tabanids, muscids,
tsetse flies), transmitted the disease, while 5% did not know anything
about the cause and transmitter of trypanosomosis. The occurrence of
trypanosomosis was high in areas bordering Abay Valley and its tribu-
taries, Bir and Temechan. In the midland areas, 80% of the respond-
ents revealed that their animals contracted trypanosomosis from the
lowland areas of the river valleys, when animals moved for grazing
and draft purposes. The only control method of trypanosomosis was
the use of trypanocidal drugs. The application of flytraps and mobile
targets, initiated by monks in the monastery with the assistance of
FAO’s Ethiopian Science and Technology Commission (ESTC) and
the Amhara Region Bureau of Agriculture, was practiced for a limited
period in 2003 (pers. commun.), and this activity created awareness
on the control methods of trypanosomosis and tsetse flies. As a result
the midland people decreased their animal movements into the low-
land areas, particularly during the rainy season.
Entomological survey
A total of 13,927 flies were caught during the late rainy season and
1731 during the dry season. The tsetse flies accounted for 1.12 and
7.79%, tabanids for 8.45 and 4.27%, while muscids for 90.42 and
87.92%, during the late rainy and the dry seasons, respectively.
The only tsetse fly species was Glossina morsitans submorsitans.
The tabanid flies included species of Tabanus, Haematopota and
Chrysops, while the muscids were mainly Stomoxys species. The
mean catches of flies by three different types of traps (monoconi-
cal, biconical and NGU) during the first study season (late rainy
season) are shown in Table I. There was a significant difference
between trap types for the mean catches of flies (p < 0.05). Since
the monoconical trap performed the best in the study areas, it was
used for the determination of the apparent fly density and statisti-
cal description.
The apparent fly density (flies/trap/day) was 1.08, 8.78 and 91 for
tsetse, tabanids and muscids in the late rainy season and 0.68, 0.35
and 7.33 in the dry season, respectively. There was a significant
difference between the seasons in the apparent density of tsetse
(p < 0.05) and also in other biting flies (p < 0.005). Altitude had
a significant effect on the apparent density of tsetse in both sea-
sons (p < 0.005) (Figure 2). Tsetse fly sexing in the study period
Trap type Mean catches/trap
Tsetse SD Tabanid SD Muscid SD
Biconical 2.29 2.44 13.76 31.63 145.47 168.31
Monoconical 3.22 2.76 26.36 46.49 274.31 382.00
NGU 1.51 2.46 11.70 41.03 131.77 377.14
Table I
Mean fly catches using three trap types during the late rainy season
SD = standard deviation
Figure 2: Tsetse apparent density at different altitudes in the
late rainy and dry seasons in the Abay Basin areas of North-
west Ethiopia.
■ PATHOLOGIE PARASITAIRE
Epidemiology of Bovine Trypanosomosis in Ethiopia
Revue Élev. Méd. vét. Pays trop., 2005, 58 (3) : 151-157
154
indicated that females were predominant during the late rainy sea-
son (88.78%) and during the dry season (53.33%). Female flies
were caught at altitude levels up to 1780 m, while male flies were
caught up to 1650 m.
Parasitological and hematological results
The overall prevalence of trypanosomosis during both seasons and
the relative prevalence of different trypanosome species are shown
in Table II. T. congolense was the most prevalent species, followed
by T. vivax and T. brucei. Mixed infections of T. congolense and
T. vivax were also recorded. The prevalence was significantly
(p < 0.05) higher in the late rainy season than in the dry season.
The frequency of infections in the dry season was 0.7 time lower
than in the late rainy season.
The prevalence of trypanosome infection in cattle was 18.45% in
males and 13.87% in females in the late rainy season, and 12.82
and 11.32%, respectively, during the dry season, but there was no
significant difference between sex groups within the same season
or between seasons. A higher infection rate (17.2%) was observed
in older animals (> 3 years) compared to young animals (< 1 year)
in which it reached only 11%. Finally, a relatively lower infection
rate of 2.56% was observed in young animals (< 1 year), while in
older animals (> 3 years) it reached 15% during the dry period.
The prevalence of trypanosome infection in the late rainy season
varied significantly between the lowland and midland areas (19.87
and 13.39%, respectively; p < 0.05), and animals in the midland
areas were by 0.7 time at a lower risk than those in the lowland
areas (Table III). The predominant trypanosome infection was due
to T. congolense at both altitude levels with 73.9 and 53.2% in the
lowland and midland areas, respectively.
The prevalence of trypanosomosis in the dry season was signifi-
cantly different in the lowland (17.62%) and midland areas (6.54%)
(p < 0.001). The predominant trypanosome infection was due
to T. congolense in the lowland areas with 94.8%, while the pre-
dominant one in the midland areas was due to T. vivax (53.8%). The
herd mean prevalence of trypanosomes in the late rainy season was
16.02% and in the dry season 12.38% (p < 0.05), and the overall
herd prevalence was 14.25%. All the sampled herds were positive
for trypanosome infections.
The PCV values of parasitemic and aparasitemic animals were
20.7 ± 3.5 and 26.6 ± 4.3 during the late rainy season (p < 0.001),
while they were 21.4 ± 3.6 and 26.6 ± 4.3 during the dry season
(p < 0.001), respectively. The range of PCV values in parasitemic
animals was from 11 to 35% and in aparasitemic animals from 14
to 43% in the late rainy season, while in the dry season the range
was from 14 to 32% in parasitemic animals and 16 to 44% in
Season Total cattle Trypanosoma species (%) Overall prevalence (%) SD
Tc Tv Tb Mixed
Late rainy 814 66.90 31.65 0.00 1.45 17.07 0.38
Dry 834 79.61 16.51 1.94 1.94 12.35 0.33
Total 1648 72.31 25.21 0.83 1.65 14.68 0.35
Table II
Prevalence of trypanosome infection in two seasons in the Abay Basin areas of Ethiopia
Tc = T. congolense; Tv = T. vivax; Tb = T. brucei; Mixed = T. congolense and T. vivax
SD = standard deviation
Season (altitude) Total Trypanosome species (%) Prevalence (%)
Tc Tv Tb Mixed
LRS (< 1600 m) 463 62.56 23.04 0 0 19.87
LRS (1600–2000 m) 351 53.19 42.55 0 4.25 13.39
Total 814 66.90 31.65 0 1.43 17.07
DS (< 1600 m) 437 94.80 3.89 1.29 0 17.62
DS (1600–2000 m) 397 34.61 53.84 3.84 7.69 6.54
Total 834 79.61 16.50 1.94 1.94 12.35
Overall total 1648 72.31 25.20 0.82 1.65 14.68
Table III
Prevalence of trypanosomes in cattle at different altitudes during the late rainy season
and in the dry season in the Abay Basin areas of Northwest Ethiopia
Tc = T. congolense; Tv = T. vivax; Tb = T. brucei; Mixed = T. congolense and T. vivax
LRS = late rainy season; DS = dry season
Epidémiologie de la trypanosomose bovine en Ethiopie
155
Revue Élev. Méd. vét. Pays trop., 2005, 58 (3) : 151-157
aparasitemic animals. The PCV values of animals in the lowland
areas were 24.8 ± 4.8 and in the midland areas 26.6 ± 4.4 in the
late rainy season, while in the dry season they were 24.5 ± 4.1 in
the lowland areas and 26.8 ± 4.1 in the midland areas.
The PCV value of the 19 herds (average 25.78%) varied signifi-
cantly with the prevalence (mean 16.02%) during the late rainy
season (p < 0.002) with a regression coefficient of –0.22. Similarly,
during the dry season the average PCV value of the 18 herds was
25.68% and the mean prevalence was 12.38% (p < 0.002) with a
regression coefficient of –0.17.
■ DISCUSSION
Over 97% of the interviewed farmers depended on mixed agri-
culture farming for their livelihood, which is consistent with the
general situation of Ethiopia where over 80% of the population
is engaged in a mixed farming system. The survey revealed that
trypanosomosis was the most important problem for agricultural
activities and animal production in the Abay Basin areas of North-
west Ethiopia settled since the 1960s. Similar results were reported
in the western and northwestern parts of Ethiopia. Trypanosomo-
sis occurs throughout the year but its incidence increases after the
rainy season and after the short rainy season. Tewelde (34), Ngare
and Mwendia (25), and Afewerk et al. (2) also reported similar
results. The absence of tsetse control activities generally makes the
farmers inclined to using chemotherapy.
Glossina m. submorsitans was the only species of tsetse fly found
in the areas. The seasonal apparent differences might result from
an absolute increase in the number of tsetse flies due to a favorable
environment such as enough moisture, vegetation growth and suita-
ble habitat, or the spread of flies from the rivers and thickets, where
they usually inhabit during the dry season, to more open areas dur-
ing the rain (4). Leak et al. (14) also cited the latter as a possible
reason for the high densities of G. pallidipes obtained during the
dry season when the traps were deployed in the Ghibe River Valley.
The increases in the tsetse apparent density during the wet season
have been reported in Ethiopia (19), Somalia (18), Cote d’Ivoire,
Togo, Gabon and Zaire (14).
The results of the tsetse fly survey agreed well with the general
knowledge on the ecology of tsetse species found in Southwest Ethi-
opia for the morsitans group. Typical habitat patterns were found in
the study areas for the savannah species G. m. submorsitans that pre-
fers savannah grass, riverine, and forest ecology. G. m. submorsitans
was concentrated in the lowland areas as climatic conditions were
more favorable. Some flies, however, were found as high as 1780 m.
Earlier works (8, 10, 11) had established the tsetse geographical limit
at 1600 m. Later, Tikubet and Gemechu (35) found the upper limit to
be at 1700 m, and NTTICC (26) and Slingenbergh (32) reported the
limit to be at 2000 m. A survey conducted by ESTC/SRVETEP (7)
in Denbecha wereda indicated that the upper limit was below 1900
m. Earlier, G. tachinoides and G. m. submorsitans were caught by
Langridge (11) in the Abay Valley areas. Tikubet and Gemechu (35)
also reported G. tachinoides and G. m. submorsitans in the Abay and
Didessa Valleys. Most of the tsetse flies in the present study were
caught in the lowland areas and the apparent density decreased as
altitude increased. This trend supports earlier works by Langridge
(11), Tikubet and Gemechu (35), and Leak (12). Slingenbergh (32)
discussed the invasion of G. m. submorsitans in the Upper Didessa
Valley, and cited a USAID report (USAID, 1976) which suggested
that the invasion of tsetse began during the 1970s and was responsi-
ble for an evacuation of the human population from the Didessa Val-
ley at that time. The Didessa and Angar Rivers are both tributaries of
the Abay (Blue Nile) River. Ford et al. (8) reported that 5902 km2 of
the river basin of the Angar, Didessa and Wama Valleys were infested
by G. m. submorsitans and G. tachinoides. G. m. submorsitans has a
wider spread habitat than G. tachinoides and G. pallidipes, and it is
also an efficient vector of pathogenic trypanosomes to domestic live-
stock. The advance of G. m. submorsitans in the Abay Basin areas of
Northwest Ethiopia as seen in the present study could have a great
importance regarding the epidemiology of bovine trypanosomosis
and human settlement. The reason for the absence of G. tachinoides
in the present study is not clear.
NGU traps are efficient for savannah species (14), but in this study
monoconical traps were the best of the three trap types used during
tsetse fly sampling. When Glossina m. submorsitans was detected
in Western Ethiopia (Gullele/Tolly area) (13), it was indicated that
biconical traps were not efficient. The apparent densities of the
tabanid and muscid flies were 6 flies/trap/day and 91 flies/trap/
day, respectively, in the late rainy season, and 0.43 fly/trap/day and
7 flies/trap/day, respectively, in the dry season.
The higher prevalence of bovine trypanosomosis was found in the
low altitude areas along the river valleys of Bir, Temechan and
Abay compared to the mid altitude areas. The seasonal occurrence
of the disease was also consistent with the general knowledge of
the vectors of trypanosomosis and hence it was higher during the
late rainy season.
The most prevalent trypanosome species in tsetse-infested areas
of Ethiopia are T. congolense and T. vivax. Rowlands et al. (29)
reported a prevalence rate of 37% for T. congolense in Southwest
Ethiopia. Abebe and Jobre (1) reported an infection rate of 58.5%
for T. congolense, 31.2% for T. vivax and 3.5% for T. brucei in
Southwest Ethiopia. Different workers (2, 24, 34) reported preva-
lence rates of 17.2, 21 and 17.5% in Metekel district, Southern Rift
Valley and Upper Didessa Valley of tsetse infested regions, respec-
tively, and the dominant species was T. congolense. The prevalence
of bovine trypanosomosis in the North Omo zone in the dry and
wet seasons was 14.2 and 21.5%, respectively (24). The dominant
trypanosome species was T. congolense (66.1%) followed by T.
vivax (20.8%). The same trend was also reported by Rowlands et
al. (30) in the Southern Rift Valley of Ethiopia. The predominance
of T. congolense infection in cattle may be due to the high number
of serodemes of T. congolense as compared to T. vivax and the
development of a better immune response to T. vivax (12, 15). It
may also suggest that the major cyclical vector is G. m. submor-
sitans, which is a more efficient transmitter of T. congolense than
of T. vivax (11). In East Africa, T. vivax is generally less virulent
(except in the hemorrhagic syndrome) than T. congolense and con-
sequently cattle develop tolerance for T. vivax more readily and
easily than for T. congolense (1).
There was a significant difference (p < 0.05) between the seasons
as the prevalence of trypanosomosis was higher in the late rainy
season (17.07%) than in the dry season (12.35%). The risks of
trypanosomosis in cattle were 0.5 time lower in the dry season than
in the late rainy season. The concurrent tsetse survey at the same
time in the same altitude areas revealed that the apparent density
was higher in the late rainy season than in the dry season. Muturi et
al. (24) reported similar results in the North Omo zone, where the
prevalence of trypanosomosis was higher in the wet season than in
the dry season.
Rowlands et al. (28) in Ghibe observed that with a decrease in the
PCV value, the proportion of infected animals increased and hence
the mean PCV was a good indicator for the health status of herds
in trypanosomosis endemic areas. The lower mean PCV value
of parasitemic animals is reported by several authors (2, 14, 24,
34). Similarly, Van den Bossche and Rowlands (36) reported that
the regression analysis of herd average PCV of parasitologically
■ PATHOLOGIE PARASITAIRE
Epidemiology of Bovine Trypanosomosis in Ethiopia
Revue Élev. Méd. vét. Pays trop., 2005, 58 (3) : 151-157
156
positive herds showed a decrease with the increasing prevalence of
trypanosome infection. The development of anemia is one of the
most typical signs of trypanosomosis caused by T. congolense in
susceptible cattle breeds (22). Bovine trypanosomosis control aims
at reducing the prevalence of infection with a concomitant increase
in the herd average PCV (3). Therefore, the knowledge of the rela-
tionship between the prevalence of trypanosome infection and herd
average PCV could be a useful tool to assess the impact of control
interventions. However, the herd average PCV is affected by fac-
tors other than trypanosomosis (5). These confounding factors are
not always identifiable but they are likely to affect both trypano-
somosis positive and negative animals. Other factors considered to
affect PCV values in animals in the study areas were helminthosis,
tick-borne diseases and nutritional imbalances. On the other hand,
most of the parasitemic animals in the lowland areas were in good
body condition despite having low PCVs. This could be attributed
to the fact that animals in low altitude areas had access to adequate
nutrition due to the availability of sufficient pasture compared to
animals in mid and high altitude areas.
■ CONCLUSION
Settlers in the Abay Basin (Denbecha and Jabitehenan) areas of
Northwest Ethiopia considered trypanosomosis as the most impor-
tant problem for agricultural activities and animal production.
G. m. submorsitans, the only prevalent tsetse fly, advanced at an
altitude as high as 1780 m, posing a risk to areas considered tsetse
free by earlier studies. The prevalence of bovine trypanosomosis
was found to be higher in the late rainy season than in the dry sea-
son. The prevalence was higher in low altitude areas compared to
mid altitude areas in both seasons. The mean PCV values of para-
sitemic and aparasitemic animals were significantly different and
the herd average PCV values were also negatively correlated to the
herd prevalence.
Acknowledgments
We thank the Faculty of Veterinary Medicine of Addis Ababa Uni-
versity, Amhara Region Bureau of Agriculture, Amhara Region
Agricultural Research Institute, Bahir Dar Veterinary Laboratory,
Denbecha and Jabitehenan weredas Office of Agriculture, and
Debre Genet Orthodox Church Monastery for their financial, logis-
tic and other supports.
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Reçu le 08.03, 2005, accepté le 13.01.2006
Résumé
Shimelis Dagnachew, Sangwan A.K., Getachew Abebe. Epidé-
miologie de la trypanosomose bovine dans la région du bassin
de l’Abay (Nil bleu), nord-ouest de l’Ethiopie
L’étude a été menée entre Septembre 2003 et Avril 2004 dans
les districts de Denbecha et de Jabitehanan situés à basse
(< 1 600 m) et moyenne altitudes (1 600–2 000 m). Les
objectifs de cette étude ont été de générer des données épi-
démiologiques sur les tsé-tsé et la trypanosomose, et sur la
connaissance de cette maladie par les communautés locales.
Les résultats d’un questionnaire ont montré que la trypanoso-
mose était le problème majeur affectant les animaux et entra-
vant les activités agricoles de la zone. Le suivi entomologi-
que a révélé la présence de Glossina morsitans submorsitans,
seule espèce de glossine de la zone, ainsi que de tabanidés
et de muscidés. Les densités apparentes (mouches/piège/jour)
ont été significativement plus élevées (p < 0,05) à la fin de
la saison des pluies (1,08, 8,78 et 91 respectivement pour
G. m. submorsitans, les tabanidés et les muscidés) qu’en sai-
son sèche (respectivement 0,68, 0,35 et 7,33). Dans les zones
de basse altitude, la densité apparente de G. m. submorsi-
tans a été significativement plus élevée (p < 0,05) que dans
les zones de moyenne altitude à chaque saison. Un total de
1 648 animaux ont été examinés pour la trypanosomose par
la méthode de centrifugation en tube microhématocrite ; les
prévalences saisonnières ont été significativement différen-
tes (p < 0,05) avec 17,07 p. 100 en fin de saison des pluies
et 12,35 p. 100 en saison sèche. Les taux d’infection ont été
plus élevés (p < 0,05) dans les zones de basse altitude (19,87
et 17,62 p. 100 respectivement à la fin de la saison des pluies
et en saison sèche) que dans les zones de moyenne altitude
(13,39 et 6,54 p. 100). Les valeurs moyennes de l’hématocrite
des animaux infectés et apparemment non infectés ont été
respectivement de 20,7 ± 3,5 et 26,6 ± 4,3 (p < 0,001) en fin
de saison des pluies et de 21,4 ± 3,6 et 26,6 ± 4,3 (p < 0,001)
en saison sèche. L’analyse de régression a montré qu’à cha-
que saison l’hématocrite moyen du troupeau diminuait quand
la prévalence de la trypanosomose augmentait.
Mots-clés : Bovin – Glossina morsitans submorsitans – Trypa-
nosomose – Epidémiologie – Facteur lié au site – Altitude –
Variation saisonnière – Ethiopie.
Resumen
Shimelis Dagnachew, Sangwan A.K., Getachew Abebe. Epi-
demiología de la tripanosomosis bovina en las zonas de la
cuenca Abay (Nilo Azul) del noroeste de Etiopía
El estudio se llevó a cabo entre septiembre 2003 y abril 2004,
en las weredas (distritos) de Denbecha y Jabitehenan, loca-
lizados en las zonas de tierras bajas (< a 1600 m) y medias
(1600-2000 m). Generó una base de datos primaria sobre la
epidemiología de la tripanosomosis y la consciencia de la
comunidad sobre la enfermedad en las áreas de la cuenca
Abay (Nilo Azul) en el noroeste de Etiopía. Una encuesta
mediante un cuestionario reveló que la tripanosomosis es
el problema principal que afecta a los animales y dificulta
las actividades agrícolas en el área. Glossina morsitans sub-
morsitans fue la única especie de mosca tsé-tsé prevalente,
junto con otros tabánidos picadores y moscas “múscidas”.
Las densidades aparentes de moscas (moscas/trampa/día)
fueron significativamente más elevadas (p < 0.05) durante la
estación lluviosa tardía (1,08, 8,78 y 91 para G. m. submorsi-
tans, tabánidos y múscidos respectivamente), que durante la
estación seca (0,68, 0,35 y 7,33, respectivamente). La den-
sidad aparente de G. m. submorsitans fue significativamente
más elevada (p < 0,05) en las zonas bajas que en las medias,
tanto durante la estación lluviosa tardía como durante la
seca. Un total de 1648 bovinos fueron examinados para la
tripanosomosis, mediante la técnica de buffy coat y la pre-
valencia estacionaria (17,07 y 12,35% respectivamente) fue
significativamente (p < 0,05) diferente. Las tasas de infección
fueron superiores (p < 0,05) en las zonas bajas, con 19,87%
y 17,62%, que en las zonas medias, con 13,39 y 6,54%,
durante la estación lluviosa tardía y seca, respectivamente.
Los valores del conteo de glóbulos rojos (PCV) de los ani-
males parasitémicos y aparasitémicos durante la estación
lluviosa tardía fue de 20,7 ± 3,5 y 26,6 ± 4,3 (p < 0,001),
mientras que durante la estación seca fueron de 21,4 ± 3,6 y
26,6 ± 4,3 (p < 0,001), respectivamente. El análisis de regre-
sión indicó que el promedio del PCV del hato disminuyó con
el aumento de la prevalencia de las infecciones de tripanoso-
mosis durante ambas estaciones.
Palabras clave: Ganado bovino – Glossina morsitans submor-
sitans – Tripanosomosis – Epidemiología – Característica del
sitio – Altitud – Variación estacional – Ethiopía.
