Page 122 - VHSA - Onderstepoort 100 Years - Part 3

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ERSTEPOORT 100
was obtained from Uganda and was used after ten further passages in embryonated eggs at Onderstepoort to produce a vaccine. It gave good results but was abortigenic in pregnant animals. Various adaptations were made to the vaccine by Kaschula and Weiss. At one stage the vaccine antigen in use had been passaged 102 generations through mice, 56 through embryonated eggs and a further 16 again through mice. Eventually it was decided to revert back to the 102 mouse passage level as it produced the best immunity. Due to its abortigenic nature and the observation by Howell that the Smithburn strain was not very effective in cattle, Barnard and Botha developed an inactivated vaccine, using a virulent field strain of RVF virus as antigen. This inactivated vaccine which is safe in pregnant sheep and cattle has been very successful and has greatly facilitated the control of RVF.
• Wesselsbron
During the summer of 1954/55 mortality of new-born lambs and later abortions and deaths among the ewes were reported from a farm in the Wesselsbron district of the Free State Province. Since the flock had been vaccinated 2 weeks before the outbreak against RVF it was thought that the live attenu- ated RVF vaccine was responsible. Intensive investigations led to the isolation of a completely new virus, named Wesselsbron virus, by Weiss, Haig and Alexander. Subsequently this virus was shown to be widespread in South Africa
Abnormal behaviour of a bull suffering from rabies
responsible duty. In many instances human contacts were involved which made a quick and reliable diagnosis essential. At times he was requested to perform diagnostic tests on human cases. One such case involved a man living in the Warmbaths district who died 5 weeks after being bitten by an insectivorous bat. The virus isolated from his brain in mice produced an atypical reaction in the fluorescent antibody test, an observation that led Meredith to believe that it was a rabies-related rather than a true rabies virus. This belief was later confirmed and
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“Intensive investigations led to the isolation of
a completely new virus, named Wesselsbron virus, by Weiss, Haig and Alexander. Subsequently this virus was shown to be widespread in South Africa and it was also isolated from wild- caught mosquitoes and from humans exposed to infected material.”
and it was also isolated from wild-caught mosquitoes and from humans exposed to infected material. Apart from newborn mice the virus was also adapted to grow in embryonated eggs and in lamb kidney cell cultures. A virus that has been passaged for 145 generations in the brains of mice was selected by Weiss as vaccine strain for the production of a commercial vaccine. It induces very good immunity in vaccinated sheep but in view of its abortigenic property it should never be used in pregnant sheep.
This is another example of a virus that was first isolated at Onderstepoort although later work showed it to be prevalent in most tropical and subtropical parts of Africa.
• Rabies
The first definite diagnosis of rabies made
was in 1929 by P.J. du Toit. Since that time routine rabies diagnosis was done in the Virology Section. This was mostly a part-time activity and most of the researchers have at some stage been responsible for rabies diagnosis.
C. (Courtney) Meredith was the first veterinarian at Onder- stepoort to be engaged in rabies diagnosis and research on a full time basis. He was particularly interested in this disease and, being extremely meticulous, was the ideal person for this highly
the virus was named Duvenhage after the victim. In 1980 Meredith also made the first isolation of Lagos bat virus in South Africa from fruit eating bats.
When both Thomson and Meredith re- located to the new FMD laboratory in 1980 rabies research was temporarily suspended while the diagnostic activities continued at the Institute. By the early 1990s Meredith had resumed his work on rabies which included a study of the epidemiological role of the yellow mongoose and an investigation of the use of PCR-based RNA sequencing to differentiate between viruses isolated from particular species and epidemiological situations. When Meredith retired the work was continued by Thomson and co-worker F. Chaparro in a collaborative programme with the Institute and with L. (Louis) Nel of
at Onderstepoort
the University of Pretoria.
Based on RNA sequencing and monoclonal antibody
typing, the important discovery was made by the mid nineties of two virus strains, the classical ‘viverrid’ type transmitted by mongooses but also by wild and domes- tic cats and a ‘canid’ type affecting mainly domestic dogs, jackals and bat-eared foxes. Differences between the epi- demiology and distribution of the two types indicated that they were introduced into the country by different routes
PART 3
History of Individual Disciplines
1908-2008
Years