Prevalence of Trypanosomosis in Ruminants in Rivers State and Abia State, Nigeria and the Challenges of Trypanosomosis Control in Goat Production

Abstract

Trypanosomosis is one of the major diseases hindering livestock production in tropical Africa. The disease negatively impacts food production and economic growth in sub-Saharan Africa. African animal trypanosomosis is a debilitating and often fatal disease of animals, caused by infection with pathogenic protozoan parasites of the genus ‘Trypanosoma’. A recent prevalence study for the infection in ruminants reared in two Southern states of Nigeria (Rivers and Abia) gave zero by the wet mount and buffy coat methods which only suggests low prevalence and may not mean that the infection has been eliminated in the country. More sensitive methods may detect low prevalence. It also suggests that common breeds of ruminants in the area may be genetically resistant to the infection or that they have acquired resistance. Relapse to susceptibility is still possible. So, prophylactic medications and other methods of control for the infection are still necessary for the area.

1. Introduction

Livestock diseases reduce agricultural output by about 30% in developing countries including Nigeria [1]. These diseases are endemic including fly-borne diseases like trypanosomosis, tick-borne diseases like babesiosis as well as helminthosis; all of which increase morbidity and mortality, reducing production and subsequently leading to hunger and poverty. Trypanosomosis is a debilitating and often fatal disease of man and animals, caused by infection with the pathogenic protozoan parasites of the genus Trypanosoma [2, 3, 4, 5]. It is an economically significant disease affecting livestock production in Nigeria and causing significant losses ranging from a decrease in production to death [6, 7]. The disease is characterized by anemia, parasitemia, fever, loss of condition, reduced productivity and frequently high mortality which among other factors limit the pace of development in tropical Africa. Trypanosomes are extracellular parasites that cause persistent infection of the blood (and/or body fluids) and induce immunosuppression [8]. Trypanosomes are widely distributed due to the abundant presence of its biological vector (tsetse, Glossina spp) [9] which covers about 80% of Nigeria's land mass; and mechanical transmission vectors, which are biting flies, like Tabanids (horse flies), Stomoxys (stable flies) and vampire bats [10]. The severity of disease caused by trypanosomes depends on the species and strain of the infecting trypanosomes [11], with T. congolense having a more severe impact than the other species, on ruminants’ health and production [12]. Infections with Trypanosoma brucei, Trypanosoma congolense, Typanosoma vivax and Trypanosoma evansi have been reported in goats [13, 14]. Concurrent infections can occur with more than one species of trypanosome [15].

Control of African Animal Trypanosomosis (AAT) includes the use of trypanotolerant breeds of livestock [16, 17], vector control [18], chemotherapeutic and chemoprophylactic agents [19] or a combination of the methods according to specific conditions of an area [20]. However, control of animal trypanosomoses relies primarily on the use of insecticides or traps to control the vector (especially in the case of tsetse-transmitted trypanosomes) and on the use of trypanocides to control the parasite [21]. The use of trypanocidal drugs for trypanosomes parasite control represents the main intervention tool in most poor rural endemic areas since vector control can be expensive when used on a large scale and is not always sustainable or effective [22, 23].

Drug resistance, relapse of infections and toxicity of trypanocidal drugs are major challenges encountered in parasite control (treatment) of trypanosomosis.

Most of trypanocides are expensive and/or toxic [24] and have the tendency to elicit drug resistance [25, 26]. Some of the trypanocidal drug-induced side effects can be serious and even life-threatening [27]. Relapse of infection, sometimes observed after treatment of trypanosomosis, has been attributed to the resurgence of parasites into blood and body fluids after the invasion of the brain tissue by the tissue-invasive Trypanosoma vivax and Trypanosoma brucei group parasites [28, 29, 30] which are inaccessible to trypanocidal drugs due to presence of a blood-brain barrier. Reports have shown that some strains of Trypanosoma brucei group of trypanosomes invade body tissues as early as four hours to four days post-infection [31, 32]. Apart from causing disease, trypanosomes are also responsible for producing a state of severe immunosuppression, which renders the infected host more susceptible to secondary infections and produces a poor immune response to bacterial and viral vaccines [8]. This is due to the reduction of their ability to mount protective immune responses against invading parasites [33]. Immunosuppression is a major obstacle to sustainable livestock production [34] and food security. The significance of immunosuppression is appreciated more in endemic areas where herd immunity against serious epizootic diseases depends on massive vaccination campaigns [35].

There is limited information on the prevalence of trypanosomosis in the southern part of Nigeria. A prevalence rate of 17.10% of ruminant trypanosomosis was recorded in a survey of livestock diseases from September 2002 to August 2003 in Enugu State, South-East Nigeria [36]. In a part of Abia State, a low prevalence rate of 1.9% was recorded in ruminants with goats having a prevalence rate of 1.2% for trypanosomosis [37]. The low prevalence rate of trypanosomosis in small ruminants compared to cattle, in Nigeria, has been attributed to trypanotolerant breeds being the majority among small ruminants [7, 38, 39]. The prevalence of trypanosomes in animals could be affected by several factors such as availability of reservoir hosts, seasonal factors, altitude, fly density and behavior, sensitivity of diagnostic techniques, stage of infection, method of sampling, conflict and other human activities [40, 41, 42].

A zero prevalence of trypanosomosis in goats was recorded recently in both Rivers and Abia States, Nigeria [43], agreeing with reports that goats are resistant to trypanosomosis [44]; however, several other studies on the prevalence of trypanosomosis in goats revealed that goats acquire natural infection resulting in economic losses [45, 46, 47]. These losses include a reduction in milk production, weight gain, reproduction and eventually death of the affected animals [48]. Goats that survive the infection become reservoirs of the parasite and endanger humans and other domestic animals [6].

The disease leads to a reduction of animal protein [49] thereby promoting food insecurity [50] and contributing greatly to underdevelopment through poverty and hunger [5, 51].

Goat production is a great source of income for commercial farmers. Goats also serve to improve the economy of peasant farmers who may not be able to keep large ruminants like cattle. They provide meat, milk, skin and manure. In Nigeria, goats can be used for important religious and social activities besides serving as cash reserves and a form of savings for rural populations or households. They serve as a source of income in times of stress, during drought and agricultural crop failure [52, 53, 54].

There is a paucity of information on the prevalence of trypanosomosis in the southern part of Nigeria, as the majority of studies on trypanosome prevalence were conducted in the northern and central parts of Nigeria. Hence, this study on the prevalence of trypanosomosis in Rivers and Abia States Nigeria, which are both in the southern part of the country, was aimed at investigating the current prevalence of trypanosomosis in cattle, sheep and goat in Rivers (South-South) and Abia (South-East) states, Nigeria.

2. Materials and methods

2.1 Study area

This study was conducted between July and October 2018 in Ahoada West LGA, Ahoada East LGA and Ikwere LGA of Rivers State as well as Umunneochi LGA and Ikwuano LGA of Abia State. Animals sampled belonged to individuals.

Geographically, Abia State occupies about 6320 square kilometers of land area, with a population of about 4,112,230 and a population density of 650/km². It lies between latitude 5.251°N–5.417°N and longitude 7.30°E–7.500°E, altitude of 244–305 m above sea level. It is a low-lying tropical rainforest. The southern portion gets heavy rainfall of about 2400 mm per year which is especially, intense between the months of April through October [55].

Rivers state occupies a total land area of 11,077 square kilometers with a population of about 5,198,716 and a population density of 635.89 per square kilometer. It lies between latitude 4°45¹N–4.750°N and longitude 6°50¹E–6.833°E. Its annual mean temperature ranges from 25°C to 28°C. Total annual rainfall decreases from about 4700 mm on the coast to about 1700 mm in the extreme north.

2.2 Sample size

The sample size was determined using the formula outlined by [56] and expected/anticipated prevalence of 3.7% for cattle; 1.1% for sheep and 1.2% for goat [17].

$$N=\left(Z^{2}pq\right)/L^2$$E1

Where:

p = anticipated/expected prevalence from similar study = [3.7% for cattle; 1.1% for sheep and 1.2% for goat, Z = 1.96; q = 1-p; N = sample size; L = allowable error (5%).

Fifty (50) cattle, twenty-five (25) sheep and twenty-five (25) goats were sampled in each of Rivers and Abia states, giving a total of 100 adult cattle (N’dama, Muturu, white Fulani and Red Bororo breeds), 50 adult sheep (WAD and Yankasa) and 50 adult goats (WAD and Sokoto red) of both sexes.

2.3 Study animals

The study was carried out on 100 cattle of breeds: 29 N’dama, 42 Muturu, 17 White Fulani and 12 Red Bororo; 50 sheep of breeds: 32 West African Dwarf (WAD) and 18 Yankasa; and 50 goats of breeds: 36 West African Dwarf (WAD) and 14 Sokoto Red selected by random sampling methods. Three herds of cattle, sheep and goats were sampled in three different locations in each of the states. The age of the animals was estimated, when not known by their owner, on the basis of the dentition, in which animals under 1 year were considered as young animals. Adult animals (above 1 year for sheep and goat; above 2 years for cattle), were sampled.

2.4 Sample collection

Blood samples were collected from the jugular vein of each sampled animal. Two (2) ml of blood was collected from each animal and put into a container with EDTA. The containers were gently rocked to homogeneously mix the blood with the anticoagulant (EDTA) in order to prevent clotting. The blood samples were either examined immediately or kept cool in a flask containing ice packs until examined microscopically within 4 hours, by wet mount and buffy coat methods.

2.5 Parasitological examination

The parasitological examination was done in the laboratory using the wet blood film [57] and microhematocrit buffy-coat methods [57].

2.5.1 Wet blood film examination

A blood film was made by placing a drop of blood on a clean glass slide which was then covered carefully with a clean cover slip so that the blood spreads evenly. The slide was placed on a microscope and the film was viewed systematically for movement of trypanosomes with x40 objective lens [58].

2.5.2 Micro-haematocrit buffy coat microscopy

A capillary tube was nearly filled (about ¾) with a blood sample and centrifuged at 2000 g for 5 min. The capillary tube was cut about 1 mm below (to include the uppermost layer of RBC) and 3 mm above (to include some plasma) the buffy coat layer. The content was gently expressed onto a slide using a micro-hematocrit capillary tube holder, mixed and covered with a cover slip. The preparation was then examined under a microscope with the ×40 objective lens [57].

3. Result

Out of the total of 100 cattle, 50 sheep and 50 goats sampled in the two states (Abia and Rivers), no positive sample was gotten. The species, number, sex and breed of animals sampled in the survey are shown in Table 1.

Animal species	Cattle								Sheep				Goat
Breed	N’dama		Muturu		White Fulani		Red Bororo		WAD		Yankasa		WAD		Sokoto Red
Sex	M	F	M	F	M	F	M	F	M	F	M	F	M	F	M	F
Number	22	7	30	12	11	6	10	2	20	12	11	7	20	16	8	6
Total No	29		42		17		12		32		18		36		14

Table 1.

Number, sex and breed of ruminants sampled for trypanosomes in Rivers and Abia states of Nigeria.

4. Discussion

The result of the survey seems to indicate the absence of trypanosome infection or zero prevalence of trypanosome infection in the studied areas. This is in agreement with the report of [59] in which N’dama and Muturu breeds among other breeds of cattle investigated in Keffi, Nassarawa State, were not infested with trypanosomes.

The result is also, in line with the report of [60] in which none of the Tsetse dissected in his work in Bassa, Plateau State was positive for trypanosomes thus suggesting a low prevalence of trypanosomes in ruminants in that area. A low prevalence rate of 1.9% in ruminants with goats having a prevalence rate of 1.2% in some parts of Abia State, has been reported [17].

There is a dearth of information on ruminant trypanosomosis in the areas studied (South-East and South-South, Nigeria), hence a lack of data for comparison.

The absence of infection or zero prevalence as observed in the study suggests a very low infection rate attributable to a decrease in the population of tsetse and other biting flies as a result of environmental, weather and anthropological changes. Since the survey was conducted on animals owned by individuals, it is also possible that farmers inject their animals with trypanocidal drugs and also use insecticide sprays to minimize the population of biting flies. The rise in human population and consequent increase in human activities causing significant changes in the availability of suitable habitats and hosts that potentially ensure tsetse survival and sustenance in a given location may also have occurred [61]. In addition, the expansion of veterinary services up to peasant associations and deforestation for crop cultivation and settlement might be a reason.

The zero prevalence observed in the area could also be due to the inadequacy of the parasite detection methods employed. The micro-hematocrit-buffy coat method used for diagnosis is still regarded as a good parasitological technique for quick detection of the parasite, allowing for quick and clear visualization [62], though it has been reported to be relatively insensitive as it fails to detect 66% of infected animals compared to molecular diagnostic techniques and serological diagnostic methods [63]. More so, trypanosome organisms are most likely to be found in the blood during the initial or early stages of the infection. They are less likely to be detected in chronically ill animals and may never be detected in healthy carriers [64].

Low prevalence or absence of infection may also relate to the reported resistance of indigenous ruminants to trypanosomes infections [65, 66, 67]. There are reports of trypanotolerance involving N’dama and Muturu breeds of cattle [68, 69], which form the majority of the sampled animals. The zero trypanosomes in Red Bororo observed in this study also agree with the report of [60] in Bassa LGA of Plateau State. This trypanotolerance could be largely due to innate resistance and natural genetic manipulation over time, to adapt to tsetse bites and partly due to their coat color that may serve as camouflage. Some trypanotolerant breeds tend to self-cure and eliminate the organism. Others may remain persistently infected but maintain productivity and show few or no signs of illness [64]. It might also be due to their hairy tail-end, used in warding off tsetse. More so, animals in the southern part of Nigeria are more or less intensively managed; extensive management of livestock has been reported to be a risk factor for trypanosomoses with higher prevalence rates compared with intensively managed animals [70].

Implications of the discovery include that Abia and Rivers States are good for sustainable livestock (ruminant) production since trypanosomosis identified as a serious constraint to livestock production and economic development in Nigeria appears to have become insignificant in the area. This, however, does not mean the infection has been eliminated. If more sensitive methods are used for purely epidemiologic studies low prevalence may be recorded. So, there is still a need to search for better and cheaper methods for prophylaxis and treatment of the disease.

5. Conclusions

Goat trypanosomosis, though of low prevalence in the southern part of Nigeria, could be of serious economic impact and public health importance, if neglected and uncontrolled.

Acknowledgments

I wish to acknowledge the efforts of the Late Prof. M.I. Ezeja, who also supervised this study but has been taken by the cold hands of death.

Conflict of interest

The author declares no conflicts of interest.