COMPARATIVE STUDIES ON THE INFECTIVITY AND PATHOGENICITY OF EXPERIMENTAL TRYPANOSOMA BRUCEI BRUCEI INFECTION IN MICE, RATS, RABBITS AND GUINEA FOWLS
The study compared the infectivity and pathogenecity of experimental Trypanosoma brucei brucei infection in mice, rats, rabbits and guinea fowls. A total of 10 each of the following animals‟ mice, rats, rabbits and guinea fowls of both sexes were used for the study. Each group of the animal species was divided into two groups (infected and control) of five animals each. The mice, rats, rabbits and guinea fowls in the infected groups were individually inoculated with blood containing 1 x106 Trypanosoma brucei brucei (Fadere stock). All animals in the control groups were not infected. Patent parasitaemia as determined by haematocrit centrifugation technique was between 3-4 days in the mice and rats, while it was 7-8 days in rabbits. No parasitaemia was seen in the infected Guinea fowl throughout the study. The mean body weights of mice, rats and rabbits decreased in the infected group as compared to the control group. All animals in the infected group with the exception of guinea fowls showed increase in body temperature. In the mice and rats there were significance diferrences (SD) (p < 0.05) in the overall mean PCV, HGB and RBC between the infected groups (IG) as compared to the control group (CG). In the rabbits there were SSD (P < 0.05) in the overall mean PCV, HGB and RBC between the IG (36.1 ± 0.6%, 12.11 ± 0.8 g/dl and 5.9 ± 0.4×106) and CG (43.7 ± 0.5%, 14.1 ± 0.9 g/dl and 7.23 ± 0.3×106 respectively). There was no SD (P > 0.05) between the overall mean PCV, HGB and RBC of the infected guinea fowls and those of the control group throughout the period of the experiment. Also, no mortality was recorded among the infected guinea fowls as consequence of the infection. A decrease in mean total white blood cell (WBC) counts of the rats and the rabbits were observed while mice and guinea fowls groups showed no significance difference between the WBC of the infected and control groups. Microscopic lesions observed in the mice, rats and rabbits included congested central vein and perivascular cuffing, congestion and mononuclear cellular infilteration around blood vessels of the lungs, depletion of lymphoid cells, congested inter tubular spaces and focal necrosis of renal tubular epithelium. In the guinea fowls, the spleen revealed heamosiderosis. The study thus demonstrated that mice, rats and rabbits are, in order of susceptibility better laboratory models than the guinea fowls which tend to show some measure of resistance to Trypanosoma brucei brucei used in the experiment. Therefore rabbits could be use in our laboratory to preserve Trypanosoma brucei brucei.
1.1 Background of the Study
Trypanosomosis is a disease of man, domestic (Fajinmi et al., 2011; WHO 2015) and wild animals (Abenga et al., 2006; Mbaya et al., 2009; 2011). It is transmitted by tsetse flies (Glossina spp.) and characterized by anaemia, oedema, cachexia, intermittent fever and death (Yakubu et al., 2014). In Africa including Asia and South America it is transmitted by several biting flies like Tabanus, Hippobosca, Stomoxys (WHO 2015; Yakubu et al., 2014).
The Trypanosoma species affecting man and his domestic animals have been subdivided into two groups, the haematic group (Trypanosoma congolense, T. vivax) which remain in the blood plasma and the tissue invading group (T. brucei brucei, T. brucei gambiense, T. brucei rhodesiense and T. equiperdum) that are found in extra and intra vascular spaces (Abubakar et al., 2005; Chretien and Smoak, 2005; Ngure et al., 2008). Because of their presence in the blood, these invading parasites produce numerous changes in the cellular and biochemical constituents of blood (Taiwo et al., 2003). Infection with Trypanosoma brucei infection like other Trypanosoma infection precipitate red blood cell destruction which results in anaemia as well as tissue damage (Ekanem and Yusuf, 2008; Akanji et al., 2009).
Clinically, the effects of trypanosomosis in animals range from anaemia, immunosuppression, depression with inability to rise, pyrexia directly associated with parasitaemia, paleness of mucous membrane, rapid pulse beat, retarded growth, roughness of haircoats. Reduced capacity to work leading to morbidity and mortality in the absence of treatment (Batista et al., 2012; Silva et al., 2013).
In addition are enlargement of peripheral lymph nodes, reduced milk production, low meat quality, and weight loss as well as reproductive disorders such as infertility, abortion, stillbirth.
In a review by Ibrahim et al., (2015), some of the pathological changes in animals (mice, rats and rabbits) include splenomegaly, hepatomegaly and nephritis, in addition, cardiomegaly has been reported in rabbits. The histopathology changes include degenerative changes in both liver and kidneys, The spleen of the mice showed giant macrophages, that of the rats showed epithelioid giant cells, while those of the rabbits showed haemosiderosis and eosinophilic infiltrations. However, exclusive to the rabbits was hydropic degeneration, necrosis and mononuclear cellular infiltrations in the myocardium. Also observed was that the liver of the mice showed central vascular congestion with sheathed artery, that of the rats showed sinusoidal haemorrhages and nuclear vacuolation while that of the rabbits showed very mild, but widespread vacuolar degeneration of hepatocytes with periportal mononuclear cellular aggregations and presence of scattered megalocytes. The report also indicated that the kidneys of the mice infected with T. brucei showed interstitial haemorrhages and necrosis of the tubular epithelial cells, that of rats showed multi-focal glomerular degenerations and tubular ballooning in the cortex while that of rabbits showed mild but diffuse interstitial mononuclear cell infiltration especially at the corticomedullary junction.
1.2 Statement of Research Problem
Although T. brucei brucei is primarily a parasite of domestic animals as well as man, laboratory animals are often used to establish the course of infection and the degree of pathogenecity of the parasite, and these animals therefore serve as models in different experimental designs to study the disease it causes. However, it has been reported from experimental studies that the course of infection and severity depends on some factors such as the host species and the strains of the parasite. These studies have not given much Information on the degree of infectivity and pathogenecity of T. brucei brucei infection in laboratory animals such as mice, rats, rabbits and guinea fowls.
Laboratory mice and rats especially have been used in laboratories to preserve Trypanosoma brucei brucei for experimental studies and some degree of pathogenecity and sometimes death have been reported (Lawal et al., 1999). It is therefore important to explore the possibility of using other animal species as experimental models for the Trypanosoma brucei brucei infection for appreciable periods with minimum loss of such animals and hence the parasites.
• Extensive work has been done on animal trypanosomosis due to Trypanosoma vivax, Trypanosoma congolense and Trypanosoma brucei (Adeiza et al., 2008; Adamu et al., 2008) but little has been done to determine and compare the degree of pathogenecity of these parasites in different laboratory animals. Laboratory animals (mice and rats) are used as models in many researches. Therefore, there is need to establish the infectivity rate and pathogenecity of Trypanosoma brucei brucei infection in these animals with the view of establishing the best laboratory animal model for use in trypanosomosis research.
The ability of laboratory animals to serve as in vivo models depends partly on the capacity to withstand experimental infection. This needs to be established in different laboratory animal models.
Laboratory rats and mice have over the years been used extensively in preservation of Trypanosoma brucei parasites but the pathogenecity of the parasites sometimes result in sudden loss of both the animals and the parasite hence the need to explore the possibility of using other animal models in comparism with mice and rats for this purpose.
1.4 Aim and Objectives of the study
1.4.1 Aim of the study
The aim of this research was to compare the infectivity and pathogenecity of Trypanosoma brucei in mice, rats, rabbits and guinea fowls
1.4.2 Specific objectives of the study
The objectives of the study were to determine and compare the:
a. Parasitaemia and its onset in mice, rats, rabbits and guinea fowls following experimental infection with Trypanosoma brucei.
b. Changes in rectal temperature induced by experimental Trypanosoma brucei infection in mice, rats, rabbits and guinea fowls.
c. Hematological changes induced by experimental Trypanosoma brucei infection in mice, rats, rabbits and guinea fowls.
a. Microscopic lesions and their distribution in the laboratory animals experimentally infected with Trypanosoma brucei
1.5 Research Hypothesis
Ho; There is no difference on the course of experimental Trypanosoma brucei infection in mice, rats, rabbits and guinea fowls.
Ha; There is difference on the course of experimental Trypanosoma brucei infection in mice, rats, rabbits and guinea fowls.