Prevalence of Bovine Trypanosomosis in Morogoro, Tanzania
The prevalence study of bovine trypanosomosis was conducted
in 43 smallholder farms which were randomly selected from 350 cattle farms
and seven medium scale farms purposively selected in Morogoro, Tanzania.
A total of 509 and 102 cross breed and local cattle, respectively aged
six months and above were used in the study. The selected animals were
examined for clinical signs of trypanosomosis and thereafter screened
for haemoparasites using direct blood smears and micro-centrifugation
methods. The overall prevalence of trypanosomosis in cattle was 2.3% (95%
CI: 1.4-3.8, n = 691). Infected animals (n = 16) had the mean rectal temperature
of 39.1oC±1.03. The mean number of parasites and PCV
was 8.6±13.6 and 24.8%±7.9, respectively. Specific infection
rates based on trypanosomas species were 0.4%, 0.6%, and 1.3% for T.
congolense, T. brucei and T. vivax respectively. A highly significant
(P < 0.05) infection rate was found in cattle on farms located in northeastern
part of Morogoro town (4.0%, n = 303) than those in the southwest (1.0%,
n = 388, RR = 3.84, 95% CI = 1.18 - 16.98). Sex, breed, grazing system,
farm size, acaricide application and chemoprophylaxis were not the risk
factors for the trypanosomosis infection. It was concluded that, despite
a continuous uses of chemoprophylaxis, synthetic pyrethroids, bush clearing
and many other methods against tsetse flies, trypanosomosis is still prevalent
in cattle in Morogoro. Animals in the livestock-wildlife interphase are
at higher risk of infection. It was recommended that trypanosomosis losses
due to cattle mortalities, reduced production and reproduction performance,
continuous disease treatment and control costs need to be quantified.
Knowing the associated losses may call for strengthening the disease surveillance,
treatment and control strategies which are aimed at reduction or total
elimination of the tsetse flies.
Bovine trypanosomosis is a major animal disease constraint to livestock
production in sub-Saharan Africa. It is estimated that some 46 million
cattle are at risk of contracting African animal trypanosomosis in sub-Saharan
Africa (Kristjanson et al., 1999; FAO, 2000). Tsetse flies, through
the cyclical transmission of trypanosomosis to both humans and their animals,
greatly influence food production, natural-resource utilization and the
pattern of human settlement throughout much of sub-Saharan Africa (SSA).
It is estimated that the annual direct production losses in cattle alone
amount to between US $6000 million and $12000 million, while animal deaths
may reach 3 million in SSA (FAO, 2000). It is estimated that over one
million tonnes of meat in SSA equivalent per year and 1.26 million tonnes
of milk per year valued at US dollar 5 billion are being lost due to trypanosomosis
infection (Jahnke et al., 1988). In Tanzania, tsetse-borne diseases,
and in particular bovine trypanosomosis is one of the two most important
diseases that are responsible for reduced livestock productivity and together
with tick-borne diseases they are responsible for 75% of the morbidities
and mortalities in cattle (Jahnke et al., 1988).
Trypanosomosis, which takes the form of an acute or chronic status, is
normally characterized by fever, anaemia and loss of productivity; with
cattle being the most susceptible domestic animal to Trypanosoma congolense,
Trypanosoma vivax and Trypanosoma brucei infections (Blood
and Radostitis, 2007). Tsetse flies are the most common vector
for the trypanosomas and they occupy up to ten million square kilometers
of Africa. In Tanzania, there different species of tsetse flies (Glossina
spp) and occupy up to two thirds of the land. The species include
Glossina morsitans, Glossina pallidipes, Glossina swynnertoni
and Glossina austeni occupying the savannah areas, Glossina
fuscipes occupying riverine and lake areas, around Lakes Victoria
and Tanganyika and Glossina longipennis and G. brevipalpis
occupying fringe forests areas (Connor and Halliwell, 1987; Ministry of
Agriculture and Co-operatives, 1998).
Trypanosomosis continues to be a menace in the livestock industry in
Tanzania despite the age long attempts to control the disease. The tsetse
flies eradication efforts should be strengthened in view of the fact that
the disease transmitted by tsetse not only affects livestock but also
humans. Because of the importance of the disease in the livestock industry,
it is necessary to have a regular surveillance and ascertain the status
of the disease. The purpose of this study was to establish the prevalence
of trypanosomosis in cattle in selected farms around Morogoro town.
Materials and Methods
Study areas, farms and animals: This study was conducted in the
urban and peri-urban areas of Morogoro municipality. A total of 43 smallholder
farms were randomly selected from a sampling frame comprising of 350 farms.
In addition, seven medium scale farms (Kingolwira, Lutheran Junior Seminary,
Shem, Mwilunga, ARU Otitis, Nasar and Ole) were purposefully selected
for convenient of shipping samples to the laboratory and willingness of
the farmers to participate in the study. After selection of the study
farms, all the animals with the six months of age in the selected farms
were screened for trypanosomosis.
The field study was conducted in both urban and periurban areas in Morogoro.
Morogoro municipality is situated at the latitude 5.7-10oS
and longitude 35.6-39.5oE, with an elevation of 1200m above
sea level and is about 200km west of Dar es salaam, the capital city of
Tanzania. Annual average rainfall ranges between 500 and 1800mm and ambient
temperature ranges between 18-28oC. The municipality areas
have a bimodal rain pattern, with about 83% of the rain falling between
late February and end of May and short rains between November and January.
The vegetation cover of the area ranging from northeastern to southwestern
parts of Morogoro town is extremely variable. It ranges from drier lowland
coastal forest habitats, to transitional rainforests, to sub-montane,
montane and upper montane forest types.
The study area was arbitrary divided into two parts; the northeastern
and southwestern parts of Morogoro town. The northeastern areas are located
towards Dar es salaam. Up to 30 km away from the town center, the area
is more occupied for human settlement and has active agricultural activities.
On the other hand, the southwestern areas have pronounced dry seasons.
To the eastern parts, the area is boarded to Mikumi national park. This
area is less populated with minimal agricultural activities but more occupied
by pastoralist herds of cattle. Twenty one small holder and three medium
scale farms were located in the northeastern area while 22 small holder
and four medium scale farms were from southwestern areas of the town.
The cattle screened were mainly were crossbreeds of Friesian, Ayrshire
and Jersey. Two farms medium and some small scale farms had local breeds
of cattle namely Borans and Tanzania shorthorn zebu. The animals were
managed under a semi-intensive management system whereby the animals were
sent out for grazing and supplemented with some cut grasses and concentrates
when animals are back-home. However, other small scale farms had their
animals under total confinement being stall fed. The use of acaricides
against ticks and flies is common and in some farms chemoprophylaxis against
trypanosomosis and helminths are routinely used. The traditional herds
of cattle were managed under pastoral system and no disease preventive
measures were given.
Screening of animals for trypanosomosis: During the farm visits
to the selected farms, herd and animal information were recorded. These
included number of the animals in the farm, breed, sex, age, use of chemoprophylaxis
and acaricides; grazing systems and the area where the farm located. General
health status of the animals was assessed and all the animals showing
signs of ill health were recorded. Thereafter, blood smears were collected
from the ear veins; air-dried, fixed with absolute ethanol and well packed
in slide racks before shipment to the laboratory. In addition, some blood
samples were collected in the heparinized capillary tubes and properly
sealed for blood packed volume (PCV) analysis.
In the laboratory the blood samples were screened for trypanosomas using
Standard Trypanosome Detection Methods (STDM) thin smear examination as
well as the microhaematocrit centrifugation buffy-coat examination as
described by Sewell and Brocklesby (1990). Briefly, the dried and fixed
smears were stained with 10% Giemsa solution for 30 minutes, washed with
tap water and air-dried then examined under the microscope at magnification
of x100 under oil immersion. Ten random fields in each smear were examined
in order to establish whether the smear was negative or positive. For
the positive smears, the trypanosomas were identified to species level
using morphological appearances and quantification of the number of parasites
(parasitemia level) was done by physical counting of the parasites (Murray
et al., 1983). PCV and Buffy coat examination was carried out as
described by (Paris et al., 1982).
General results: Up to 56% of all the farms were located in the
southeastern part of the Morogoro town. Both smallholder and medium scale
farms, were dominated with crosses of local with exotic breeds of cattle
accounting up to 85.2% (n = 589) and the local breeds were 14.5% (n =
102). Of the screened animals, 78% were female animals and 22% were males.
All the small scale and 74% of the medium scale farms screened were using
acaricides routinely. Ninety percent of all farms were grazing their animals
outside in the field. Most of the farms (87%) under study were using isometamedium
chloride as a control of trypanosomosis at the interval of three months.
Trypanosome screening results: The overall prevalence of trypanosomosis
in cattle was 2.3% (95% CI: 1.4-3.8, n = 691). The infected animals (n
= 16) had the mean rectal temperature of 39.1oC±1.03,
with the mean number of parasite and PCV being 8.6±13.6 and 24.8%
±7.92, respectively. Interestingly, one animal had parasitaemia
level of up to 58 trypanosomas in 10 fields and the PCV was 16%. Results
on prevalence and risk factors of trypanosomosis in cattle are summarized
in Table 1. Specific infections rates based on trypanosomas
species were 0.4, 0.6 and 1.3% for T. congolense, T. brucei and
T. vivax respectively (Table 1). Of the 16 trypanosome
isolated identified, 56.25% (n = 9), 25.0% (n = 4) and 18.75% (n = 3)
were T. vivax, T. brucei and T. congolense respectively.
A highly significant (P < 0.05) infection rate was found in cattle
of farms located in northeastern part of Morogoro town 4.0% (n = 303)
than those in the southwest 1.0% (n = 388, RR = 3.84, 95% CI = 1.18-16.98).
The northeastern part of Morogoro is known to have high tsetse fly challenge
since it is towards Mikumi national park. Cattle sex, breed, grazing system,
farm size, acaricide applications and chemoprophylaxis were not associated
This study has demonstrated that trypanosomosis is prevalent in cattle
in Morogoro and is among the limiting factors to cattle production industry.
The species isolated in the survey were T. congolense (18.75%),
T. brucei (25.0%) and T. vivax (56.25%) being the most prevalent
spp in cattle of Morogoro. Such findings are in line with other studies
by Msolla (2001), Mbwambo et al., (1988), Eisler et al.
(1999) and Peregrine et al. (1988). However the prevalence of trypanosomosis
recorded in this study is low compared to that reported by Connor and
Halliwell (1987) who reported the prevalence of 16% in southern Tanzania.
The lower prevalence might be attributed by regular use of trypanosome
chemoprophylaxis as most farmers (86%) were using isometamedium chloride
since were aware of the disease and its control. Moreover, the weekly
use of pyrethroids acaricides against ticks probably has contributed to
the reduction of tsetse fly density. For instance, in the study conducted
by Msolla (2001), a 93% reduction of tsetse flies in Melela was reported
following the use of alpha-cypermethrin 10% preparation. Dipping animals
in synthetic pyrethroids appeared to have inadvertent positive effect
of also controlling tsetse flies at Kambala area in Morogoro (Mbilu et
al., 2007). Increased urbanization, villagelization and clearing of
bushes in preparation of land for agriculture and settlements may have
significantly contributed in the reduction of tsetse flies density and
consequently the reduced prevalence of trypanosomosis as was also reported
by Reid et al., (2000) and Thornton et al. (2006). However,
the low prevalence rate could also be due to the use of less sensitive
diagnostic tools (blood smears and micro-centrifugation) in this study.
The effect of trypanosome on these animals range from anaemia, immunosuppression,
retarded growth, low milk production and weight loss as well as infertility,
abortion, stillbirth and depressed reproductive performance (Elhassan
et al., 1994; Losos and Ikede, 1972). With the current prevalence,
the disease still causes losses by poor meat and milk production, increased
costs for treatment and control which all lead to losses to farmers. The
importance of cattle industry in the economy of the Tanzania cannot be
over emphasized as it contributes up to 24% of the agricultural Gross
Domestic Product (GDP). Therefore with existence of trypanosomosis despite
the age long attempts to control the disease, more efforts and targeted
strategies are needed to rescue the industry. Continuous intensified surveillance,
treatment and control of trypanosomosis and its vectors can make the disease
remain as a history. The expected spin-off effects from tsetse-trypanosomosis
control on the socio-economy of the livestock keepers communities
are increased production and reproduction performance of their animals
and hence improved likelihood of the rural poor. Indeed, it is argued
that the tsetse-trypanosomosis problem has been contributing significantly
to increased poverty among the pastoral and agropastoral communities in
The establishment of trypanosomosis at higher infection rates in cattle
which belong to the farms located in the northeastern part of the Morogoro
town suggests high tsetse challenge. These areas are towards Mikumi national
park whereby there many tsetse flies in the wild animals which are the
potential reservoirs for trypanosomosis. Moreover, the northeastern part
of the town has much vegetation cover dominated by acacia and combretum
species. Such kinds of vegetation give a favourable habitat for the tsetse
Most animals which were trypanosome positive were clinically normal with
the mean rectal temperature, number of parasite and PCV being 39.1oC±1.03,
8.6±13.6 and 24.8%±7.92, respectively. The normal clinical
parameters in infected cattle may suggest that the animals probably were
affected by the chronic form of the disease. Such animals look clinically
normal which is contributed by the balance established between the parasite
and the host and such animals remain carrier for longer periods. However,
for the infected animals to develop clinical manifestation, sometimes
depends on the dose of trypanosome inoculated, strain of the pathogen
and the host. Indeed, the severity of the disease varies with species
and age of the animal infected. Surprisingly, one animal had parasitaemia
level of up to 58 trypanosomas in 10 fields, rectal temperature of 40oC
and the PCV was 16%. The animal died two days post diminazene treatment.
Normally anaemic animal in poor condition in an endemic area suggests
trypanosomosis as was the case for this animal. Comparatively, the local
cattle are said to be more resistant to many infections including exotic
ones and their crosses. This explains also the fact that of the 100 indigenous
cattle screened in this study which were neither dipped in acaricide nor
given chemoprophylaxis while were kept only 20km to Mikumi national park
where there is high tsetse challenge had only one animal being trypanosome
|| Prevalence and risk factors for trypanosomosis in cattle
|* Significantly different p<0.05
The dominance of T. vivax in cattle affected by trypanosomosis
recorded in this study is a further confirmation of the earlier findings
(Mbwambo et al., 1988; Silayo and Mkoma, 1988; Msolla, 2001) in
different parts of Tanzania. However, the current findings are different
from those of Connor and Halliwell (1987) who reported a specific species
infection rate of 56% for T. congolense in cattle, 17% and 2.2%
due to T. vivax and T. brucei respectively. Trypanosoma
vivax is the most dominant species of trypanosome in east Africa.
Jordan (1974) reported that trypanosoma infection rates in tsetse flies
vary greatly from species to species, with T. vivax ranking
the highest and T. brucei species ranking the lowest. Indeed, T.
vivax higher infection rate may partly be contributed by its means
of transmission since it can be transmitted mechanically by biting flies
like Tabanus spp. and the pathogen can even occur in absence
of tsetse flies. In general, infection rates of the trypanosomas in cattle
determined by the number and parasite in place, the host susceptibility,
availability of the vector and the environment.
In conclusion, despite a continuous use of chemoprophylaxis, synthetic
pyrethroids, bush clearing and many other methods against tsetse flies
trypanosomosis is still prevalent in cattle population in Morogoro. The
farms located in the northeastern part of the Morogoro town are more affected
by the disease meaning that the increased tsetse challenges in the livestock-wildlife
interphase have an inadvertent positive effect on trypanosomosis in domestic
animals. In addition, the losses due to cattle mortalities, reduced production
and reproduction performance, continuous disease treatment and control
costs are yet to be quantified. In the absence of a vaccine for trypanosomosis
and with the looming threat of trypanocidal drug resistance, the only
means of controlling the disease is through controlling the vector population.
Although complete eradication of the vector is impossible, the most successful
attempts at controlling tsetse flies should aim at a significant reduction
of tsetse flies density and their contacts with cattle.
The authors highly acknowledge the livestock owners for accepting to
use their animals in this study. Likewise, we would like to acknowledge
the assistance of Drs. Lema P.J.K. (KV clinic) and Temba, P (SASI Clinic)
for providing us with a good link with the study farms. Field and laboratory
work rendered by Mr. D.K. Mabagala, A. Kitime, P. Mkuchu and F. Chambo
in the course of the trial is highly acknowledged.
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