Page 113 - VHSA - Onderstepoort 100 Years - Part 3

ONDERSTEPOORT 100
Onderstepoort also played an international role in the AHS field. In 1944 Alexander assisted during the outbreak in Egypt and Palestine, isolating the responsible virus and making the polyvalent vaccine available. Howell was actively involved in the outbreak in the Near and Middle East in 1960, visiting several countries to discuss control strategies. In 1963 Onderstepoort was appointed as OIE World Reference Centre for AHS with Erasmus as the responsible scientist, a function he fulfilled until 1995. Diagnostic services were rendered to many countries and diagnostic reagents were supplied to numerous laboratories including Plum Island, Pirbright and Geelong.
During the 1987 to 1989 outbreaks of AHS in Spain and Portugal, Erasmus visited these areas on several occasions as OIE representative and to assist with virus serotyping as well as discussing methods for control and eradication. Onderstepoort Biological Products supported the efforts by supplying vast quantities of AHS vaccine, initially in 1987 the polyvalent vaccine and, subsequent to identification of the causal virus as AHS Type 4, the relevant monovalent vaccine.
efficient when used as monovalent vaccines (e.g. serotype 4 in Spain, Portugal and Morocco in 1988 and 1989) problems were still being encountered when using a combination of vaccine strains. At least some of these serious reactions in a low percentage of horses may be as a result of genetic reassortment, resulting in some vaccine strains regaining partial or full virulence.
The susceptibility of zebras to AHS has
been known for a long time but no detailed
information was available, e.g. on the level
and duration of viraemia. Observations were
also made in several laboratories of elephant
sera giving positive reactions in complement
fixation tests but never in neutralization
tests. In attempts to find answers to these
questions an experiment was planned at Skukuza with the assistance of the late Eddie Young and officials of the Kruger National Park (in particular Dr U de V (Tol) Pienaar). Five young zebras and two young elephants were artificially infected with AHS virus and regularly bled for the detection of virus and antibodies. The results confirmed the susceptibility of zebras. Viraemia was present in one zebra for as long as 27 days post-
infection. At 40 days post-infection none of the animals showed viraemia but one animal had virus in various organs. Except for mild supraorbital oedema the zebras showed no clinical signs of disease but developed neutralizing antibodies. No virus could be isolated from the blood of the two elephants over a period of 40 days and no neutralizing antibodies developed against the inoculated virus. Elephants therefore appear to be not susceptible to AHS virus and the strange serological reactions may reflect a peculiar behaviour of elephant sera in the complement fixation test.
The overwintering of AHS viruses from one year to the next was another vexing problem for many decades. It has long been recognised that the first AHS cases occurred
in the northern lowveld regions (e.g. around Nelspruit) from where they extended in a southward direction. This riddle was eventually solved by Barnard in the 1990s when he demonstrated low level virus activity in young zebra foals in the Kruger National Park during the winter months. With the onset of spring, the infection could possibly be transferred to horses outside the borders of the Park from where subsequent
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Virology
1908-2008
Years