INTRODUCTION

Trypanosomiasis is an important insect-borne protozoan disease and a serious constraint to livestock production and economic development in many parts of sub-Saharan Africa (1). It is widely distributed in tropical and subtropical regions and its epidemiology is determined by the ecology of its insect vector, the tsetse fly (Glossina spp). Canine trypanosomiasis is a devastating disease (2) characterized by anemia, severe weight loss, muscular weakness, abortion, corneal opacity, blepharitis, conjunctivitis, keratitis and death if untreated in affected dogs (3). Trypanosomiasis of dogs was first described in 1908 (4) and it is caused mainly by Trypanosoma brucei brucei (5), Trypanosoma congolense (6), Trypanosoma cruzi (7), Trypanosoma evansi (8) and Trypanosoma caninum (9). In Nigeria, trypanosomiasis in dogs due to T. brucei and T. congolense occurs more frequently (10). It has been established that different domestic animals including dogs are potential links for trypanosome exchange between livestock and humans i.e. Trypanosome brucei gambiense and Trypanosome brucei rhodesiense, causing a condition known as HAT, also referred to as ‘sleeping sickness (11, 12, 13), while T. brucei brucei causes severe to fatal infections in horses, camels, dogs and cats (14).

There has been increased interest in keeping dogs in Nigeria, mainly as security or pets, and in some parts of the country for food. Similarly, the proceeds from the sales of dogs serve as additional income for the owners (15). Though dogs are known to pose minimal risk for human infection (HAT), they are important as a sentinel for infection (13). Canine trypanosomiasis has been reported as constituting a major health threat to canine population in the south-eastern part of Nigeria (10, 11, 16).

The study area is an interface between the hitherto declared ‘tsetse-free’ zone of the northwest and tsetse endemic areas southward in the middle belt of Nigeria. The people in the study area are predominantly crop farmers whose activities are restricted to the short period of rainfall. The long dry season is used mainly for hunting in which the expeditions takes them south, where tsetse flies abound (17). The study therefore investigated possible incursion of trypanosomes to the study area through dogs.

MATERIAL AND METHODS

RESULTS

Preliminary census enumerated a total number of 510 Nigerian local breed of dogs from households in 14 locations namely: Bayan Tasha, Filin Jirgi, Gomawa, Jarkasa, Low cost, Mangorori, Rikoto, Roadblock, Sabuwar Kasuwar, Sha da Wanka, Tudun Wadata, Unguwar Zuru, Zango, Zuru Center and a dog market. As shown in Table 1, Rikoto had the highest number of dogs (n=77), while Mangorori had the lowest (n=11). A total of 192 Nigerian dogs were selected comprising of 135 dogs from the households and 57 dogs from the dog market.

Table 1. Dog population structure with the number of sampled and positive cases in households and dog market in Zuru area, Kebbi State

Out of 192 blood samples analyzed by STDM, 4 (2.08%) were positive for trypanosomes. Out of these wet blood film detected all the 4 positive cases, microhaematocrit detected 3, while Giemsa stain (thin blood) technique detected 2 (Table 2).

Table 2. Distribution of positive samples and anemic indicator values

Morphologically, all the positive samples were identified to be in the Trypanosoma brucei group (Fig. 1).

Figure 1 Giemsa stained Trypanosomabruceion thin film smear

The PCV values ranges and FAMACHA scores of all sampled animals were not consistent with their anemic statuses. According to PCV values, of the 192 dogs examined 50 (26.04%) dogs were anemic (21), with 3 (1.56%) being positive for trypanosomes and 47 (24.47%) negative for trypanosome infection, while out of 142 (73.95%) non-anemic dogs, 1 (0.52%) was positive for trypanosomes and 141 (73.43%) were negative (Table 3). Of the 135 household-dogs sampled, FAMACHA® gave a total of 104 (77%) dogs with anemia. FAMACHA® testing was not done for dogs from the dog market (Table 4).

Table 3. Anemic status of examined dogs at different locations in Zuru using PCV

Table 4. Anemic status of examined dogs at different locations in Zuru using FAMACHA®

All the 135 respondents claimed that their dogs were kept mainly for security purposes and it was observed that dogs were mostly unleashed and found roaming about in the study area. As shown on Table 5, 21 (15.6%) of the respondents feed their dogs occasionally, 74 (54.8%) did not vaccinate their dogs against any disease, only 5 (3.7%) have their dogs receive regular veterinary health care services, while 53 (39.3%) have dogs infested with ticks and 86 (63.7%) having to dispose their dogs due to illness. Virtually all adult dogs were involved in hunting expedition during the dry season period. The hunting for game animals goes beyond the boundary of Zuru Emirate, it extends southwards into Niger and some parts of Kwara States, Nigeria.

Table 5. Responses to the questionnaire survey on dog management within Zuru

DISCUSSION

There is little information on canine trypanosomiasis in Nigeria and its epidemiology is poorly understood. In the study area and its environs, there are no previous prevalence studies making this study a preliminary study. When compared with prevalence obtained in endemic parts of Nigeria, the obtained prevalence of 2.08% in this study could be considered higher and calls for concern as the study area is previously known to be free of trypanosomes. According to other studies, the prevalence of trypanosomiasis in dogs was 3% in Jos Plateau (24), 8.8% in two veterinary clinics in Anambra State (10) and 10% in Nsukka area of Enugu State (11). The detection of Trypanosoma brucei trypanosomes in the current study is in agreement with Anene et al. (11); Abenga et al. (12); Omamegbe et al. (10) and Anene et al. (16), who reported that Trypanosoma brucei is the predominant species involved in canine trypanosomiasis in Nigeria. The presence of trypanosomes in the study area can be attributed to factors such as the unrestricted movement of dogs through commercial purposes, hunting expeditions into endemic areas and existence of Glossina palpalis palpalis both in the wet and dry seasons in areas where hunting expeditions normally take place (17).

Anemia is one of the pathogenic consequences of trypanosomiasis (22). However, the high percentage of the animals showing various levels of anemia may be due to extraneous factors such as the state of nutrition, the presence of other inter-current infections such as helminthes, which is a common problem of developing countries and ubiquitous in livestock and other domestic animals (25) and stress caused by long trekking and distant transportation. From PCV values and FAMACHA® scores, all dogs infected with trypanosomes were anemic except in one dog, with PCV of 36% but a FAMACHA® score of 4. This inconsistency may be as a result of haemoconcentration in the animal (26), or could also indicate recent infection. The leucopenia observed in two of the positive samples (Rikkoto and Unguwar Zuru) could be an indication of early infection (27), but the normal leucocyte counts from the other two positive samples from the Dog market and Filin Jirgi could not be explained.

CONCLUSION

Findings of this study establish the presence of Trypanosoma brucei group in dogs which were found in a free-HAT zone and they pose a risk for human and livestock health. Morphologically, Trypanosoma brucei brucei and Trypanosoma brucei gambiense are indistinguishable. Therefore molecular testing is suggested in further studies in order to confirm if Trypanosoma brucei gambiense is present in the population. Also, appropriate measures which include public health awareness and improvement on veterinary health care delivery services be made more readily available in the study area.