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Title: Studies on babesiosis, with particular reference to chronic parasitaemias
Author: Trees, Alexander John
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1976
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The thesis describes observations carried out on infections caused by various Babesia spp. in mice, rats and cattle with particular reference to a study of parasitaemias after acute infection. Of mice infected with Babesia rodhaini, 95% died. The mortality rate was not affected by decreasing the number of parasites inoculated, although the time to death was proportionately increased. Rats infected with B. rodhaini usually survived after varying degrees of illness and moderate parasitaemias. Parasitaemias fell rapidly from peak levels to latency. In most rats persistent infections were not detectable by subinoculation or splenectomy beyond ten days after the onset of latency. Subinoculation was shown to be an extremely sensitive means of detecting infection. Rats which naturally effected a sterile cure were immune to homologous challenge for at least a year. All mice infected with B. microti recovered. The primary parasitaemia declined in a series of progressively smaller recrudescences. Persistent parasitaemias remained patent in some mice for as long as a year. The magnitude and occurrence of chronic patent parasitaemias did not decrease with increasing time from infection. B- methasone administration had no significant effect on chronic parasitaemias. Babesia divergens infection in splenectomised calves was characterised by moderate parasitaemias accompanied by fever, anaemia, haemoglobinuria and some deaths. The decline in packed cell volume (P.C.V.) was associated with the fall in parasitaemia rather than with its rise. There was a positive correlation between the degree of anaemia and the level of maximum parasitaemia. In non - splenectomised cattle, infection produced only low and transient parasitaemias. Chronic parasitaemias were monitored daily in splenectomised calves by the examination of thin blood smears stained with acridine orange. In this way, 105 erythrocytes in each smear could be quickly examined. Parasitaemias fluctuated with frequent and regular spontaneous recrudescences. The pattern of recrudescences was not affected by the administration of B- methasone or adrenocorticotrophic hormone (A.C.T.H.), but recrudescences were provoked by beginning to handle and sample the cattle. Relapse parasitaemias were of low magnitude and were not accompanied by anaemia or other clinical signs. The indirect fluorescent antibody (I.F.A.) test was used to determine the antibody titres in primary and chronic infections. The response of splenectomised calves and non -splenectomised cattle was similar. After infection, antibodies were not detectable until maximum parasitaemias were reached. Titres continued to rise as parasitaemias fell, maximising 30 -40 days after infection. There was no difference between mean maximum titres of splenectomised and non -splenectomised cattle. Titres persisted for at least 500 days. Changes in titre were detected neither in association with recrudescent parasitaemias nor with A.C.T.H. and B- methasone administration. In Nigeria, B. bigemina was isolated from latently infected indigenous cattle. The original isolate contained six other species of haemoparasite. These contaminants were eliminated by a series of rapid passages in splenectomised calves, and a pure isolate of B. bigemina was obtained. Six non -splenectomised adult steers were infected with the impure isolate of B. bigemina, and ten similar cattle were infected with the pure isolate. In splenectomised calves, moderate parasitaemias caused severe disease with fever, anaemia, haemoglobinuria and death in 3/5 animals. The onset of anaemia was associated with the crisis of parasitaemía rather than with its rise. In non -splenectomised steers, infection caused low parasitaemias and minimal symptoms of disease with a variable degree of anaemia. The depression of P.C.V. was correlated positively with the magnitude of maximum parasitaemia. The I.F.A. response was similar in splenectomised and non -splenectomised cattle. Antibody was first detected between one and five days after maximum parasitaemia. Maximum titres were not significantly different in splenectomised and non -splenectomised cattle and were reached between 16 and L10 days after infection. In the six steers infected with an impure isolate of B. bigemina, chronic parasitaemias were monitored for 115 days. Anaplasma marginale was frequently patent during this time and a reciprocal relationship was noted between it and B. bigemina, with the former parasite apparently dominant. Falls in A. marginale parasitaemia were followed by recrudescences of B. bigemina. B- methasone administration was followed by B. bigemina recrudescent parasitaemias in 2/6 animals. In the other four animals a response appeared to be abolished by the presence of A. marginale. In the ten steers infected with a pure isolate of B. bigemina, parasitaemias generally remained latent after primary parasitaemia. Relapse parasitaemias were provoked in 8/8 animals treated with B- methasone although a pre -existing infection of A. marginale in some cattle inhibited this response. Two animals showed minor recrudescences of B. bigemina after A.C.T.H. treatment. The chronic B. bigemina parasitaemia in one splenectomised calf was observed for 79 days. Throughout this period the parasitaemia remained patent and fluctuated periodically. The feeding of non -infected ticks did not affect the parasitaemia, but B- methasone treatment was followed by a major recrudescence which caused a moderate fall in P.C.V. Exotic cattle imported to Nigeria were regularly bled for serum over a 14 month period during which they were exposed to limited natural tick infestation. Five out of fifty cattle became infected with B. bigemina as was evidenced by a change in their I.F.A. status, but none was clinically ill nor was the milk yield affected.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available