Page 120 - VHSA - Onderstepoort 100 Years - Part 3

OND
ERSTEPOORT 100
The protracted commissioning period which the FMD Laboratory went through in the early 1980s enabled other work with animal pathogens, chiefly African swine fever (ASF). Both Pini and Thomson had previously been involved with this work at the OVI’s Virology Section. Apart from introducing modern diagnostic methods for this disease, one of the results of work on ASF was the demonstration that neonatal warthogs (i.e. animals still confined to the burrows they are born in) develop viraemias high enough to infect Ornithodorus sp. ticks, which showed that ASFV behaves as a true DNA arbovirus in its natural state.
Subsequently, the successes achieved with the
molecular epidemiology of FMD were applied to
ASF, initially by Bastos and later by others including
Vosloo, A. (Alison) Lubisi and Dwarka. The research
on this pathogen has expanded significantly and
currently also includes developing a vaccine to this
pathogen that has proven elusive up to now (Vosloo and L. (Livio) Heath).
• Canine distemper
In the early part of the 20th century canine distemper (CD) was a very serious canine disease which occurred
in most parts of the world, including South
Africa. The aetiology of the condition was
Cow with symptoms of lumpy skin disease
In 1943 a similar disease appeared in Ngamiland (northern Botswana). Towards the end of 1944 it crossed into South Africa (Marico district). It was unmistakably a new disease, which was aptly named ‘knopvelsiekte’ (lumpy skin disease). In 1945 and 1946 the disease spread across the country causing
serious economic losses.
Right from the outset attempts were
made at Onderstepoort to isolate the causal agent, which was accepted to be a virus. Several viruses were isolated from clinical material, particularly since cell cultures were used in 1956. None of these isolates could reproduce the disease and were regarded as ‘orphan’ viruses, a term very common at the time in medical and veterinary virology. One of the viruses isolated by Haig and Alexander and later by Weiss produced a clinical syndrome which was difficult to distinguish from LSD. This virus was termed Allerton virus (later identified as a herpesvirus) and caused a less severe illness with more superficial nodules, later called pseudo lumpy skin disease.
a highly controversial issue for a long time. The eventual acceptance of its viral nature and the demonstration that ferrets are highly susceptible to it resulted in rapid scientific progress. The most significant
210 outcome was that serial passage of the virus in ferrets resulted in attenuation of the virus for dogs. Although many different vaccines were soon developed, none proved to be completely safe and efficacious.
“Towards the end of 1944 it crossed into South Africa (Marico district). It was unmistakably a new disease, which was aptly named ‘knopvelsiekte’ (lumpy skin disease). In 1945 and 1946 the disease spread across the country causing serious economic losses.”
At Onderstepoort Haig succeeded in
cultivating ferret-adapted CD virus (Green’s
distemperoid virus which was used as a
vaccine) in embryonated chicken eggs at
35°C. The virus was serially passaged in
embryonated eggs for up to 200 generations and various passage levels tested in dogs. Eventually the 123rd passage level was selected in 1953 as final vaccine candidate. This vaccine was completely safe in dogs as well as in other Canidae and even in ferrets. This is one of the safest and most efficacious vaccines ever produced and is currently used world-wide by all major producers of canine vaccines, a real feat (analogous to Sterne’s anthrax vaccine) achieved by a dedicated researcher and a major milestone reached at Onderstepoort.
Eventually a virus was isolated (the Neethling isolate) by Alexander, W. Plowright (a visiting scientist from Kenya) and Haig which could produce classical LSD upon inoculation of susceptible cattle. Cattle that had recovered from natural LSD possessed antibodies that neutralized the Neethling virus, confirming its aetiological role. A great deal of research work followed on growth characteristics of the virus and its cytopathology as well as the pathology of the disease and persistence of virus in blood, internal organs and, particularly, in skin lesions. However, the most logical and most pressing research need was the development of a safe and effective vaccine. In 1957 Haig, as well as Alexander, reported partial success in cultivating LSD virus on the chorio-allantoic
• Lumpy skin disease
In 1929, an apparently new disease, termed ‘pseudo-urticaria’ was noticed in the then Northern Rhodesia (now Zambia).
PART 3
History of Individual Disciplines
1908-2008
Years