Page 73 - VHSA - Onderstepoort 100 Years - Part 3

cattle showing a patent parasitaemia. Potgieter conducted a series of funda- mental investigations in the 1970s on the life cycle of B. bigemina and B. bovis (first diagnosed in South Africa by Neitz in 1941, although probably present much earlier) in the vector ticks and in cattle, which included studies on the fine structure of the parasites. This research placed the more practical studies that were to follow on a sound scientific footing (see below). He was awarded a PhD in Zoology on the strength of a thesis on the life-cycle of B. bovis and B. bigemina in cattle and ticks in 1977 by
the Rand Afrikaans University.
P.R. Barrowman joined the Section of
Protozoology in 1973. In the ensuing years
he conducted a thorough and clinically
elegant investigation of the pathogenesis of
dourine for which he was awarded a DVSc-
degree in 1977. He followed the course of
the pathogenesis in relation to the presence
of the causative trypanosome (Trypanosoma
equiperdum) in the body at various stages
of the sequence of clinical events that
develop after natural infection and showed
that transmission is more likely to occur
when a recently infected stallion or mare
is involved as vector. Although parasites
are present in the blood in early cases,
they are rare and centrifugation of blood
is necessary to demonstrate their presence. Parasites are also present in small numbers in the discharges from the genitalia. The onset of the nervous form of the disease coincides with the presence of the parasites in the cerebrospinal fluid in which parasites can sometimes be sufficiently plentiful to be demonstrated microscopically.
Shan Thomas joined the Protozoology Section in 1970 where she worked for 10 years. Apart from her research on mortality in roan antelope calves caused by a Cytauxzoon sp., she conducted experiments, continued more extensively by others in the 1980s (particularly L. Diesing from Germany), to try to confirm the hypothesis that B. besnoiti of cattle has a carnivorous final host. The following species were exposed to cyst-bearing material obtained from naturally infected cattle by the oral route: puff adder, leopard, lion, cheetah, domestic cat, black-backed jackal, Cape fox, banded mongoose and white- backed vulture. One of the leopards and two of the banded mongooses shed low numbers of Isospora-type oocysts in their faeces, but two cattle infected with 20 000 oocyts per os each showed no evidence of infection. Diesing also demonstrated that it was possible to consistently produce a severe form of besnoitiosis experimentally in cattle that were immuno- suppressed with corticosteroids prior to artificial infection with cystozoites or endozoites of B. besnoiti. K. Janitschke (a
ONDERSTEPOORT 100
visitor from Germany) and local co-workers developed immunofluorescence and ELISA tests for serological surveys of besnoitiosis in 1983.
Bigalke was promoted to Deputy Direc- tor of Onderstepoort in 1974 and was re- placed by De Vos as head of the Section. The redwater vaccine was further improved in the 1980s and eventually replaced by D.T. de Waal and Combrink in 1998 with separate, standardized, frozen B. bigemina and B. bovis vaccines, which could be subjected to full quality control procedures prior to use.
Further improvement of the anaplas- mosis vaccine by Potgieter resulted in the development in 1990 of a frozen product containing a standardized number of orga- nisms per ml, similar to the Babesia vaccine. Potgieter has also proved that transovarial transmission of Anaplasma marginale in the one-host ticks Boophilus decoloratus and Boophilus microplus does not occur, which is contrary to the finding published by Theiler many years before. Transstadial and intra-stadial transmission are, how- ever, possible. It is clear that these ticks must move around a lot more than their one- host life cycle suggests. He also identified Rhipicephalus simus as a vector and studied the development and ultrastructure of A.
marginale in this tick.
Potgieter also conducted sterling work on the preser- 163
vation of infective stages (stabilates) of Babesia and Theileria present in the respective vector ticks at the very low tempe- ratures provided by liquid nitrogen (cryopreservation). He also discovered that primaquine phosphate (historically used as an anti-malarial in humans) was highly effective for treating domestic cats that contract Babesia felis infections. Based on the published work, this treatment regime was commercialized and is still in use.
In 1982 de Vos left for Australia to join L.L. Callow at the Tick Fever Research Centre at Wacol in Queensland and Potgieter took over as head of Protozoology. Potgieter was awarded the prestigious BP Post-graduate Scholarship in Agriculture in 1981 and spent a year of sabbatical leave in 1982 – 1983 at the Oklahoma State University, Washington State University and Texas A&M University, the latter as visiting professor. He thus developed excellent collegial ties with overseas scientists working in his field of expertise such as Prof Kathy Kocan of Oklahoma State University, who later spent time at Onderstepoort studying the fine structure of the causative organism of heartwater, Ehrlichia ruminantium.
T.E. Mason, who became a member of the Section in the late 1970s, did not stay for long but his research made
“Potgieter was awarded a PhD in Zoology on the strength of a thesis on the life-cycle of B. bovis and B. bigemina in cattle and ticks in 1977 by the Rand Afrikaans University.”
Protozoology
1908-2008
Years