Volume 23 • Issue 02 • 2019
Moreover, international perceptions concerning
FMD, not to mention control strategies/norms
and trade standards, are almost exclusively based
on Eurasian type FMD. That situation makes life
difficult for countries like Botswana, Namibia and
South Africa. The extent of the differences between
the SAT and Eurasian lineages, my colleagues and
I have shown, renders the eradication of SAT
viruses in Southern Africa technically difficult,
if not impossible, using currently available
technology, i.e. unlike the situation with the
Eurasian types. The implication is that in the long
term FMD will be eradicated from most parts of
the world but not Southern Africa.
Differences between SAT and
Eurasian FMD
The ability to manage effectively and/or eradicate
transboundary animal diseases, of which FMD is
a prime example, is dependent primarily on three
factors: (1) the epidemiology of the disease, (2)
the ability to identify accurately the presence of
the infection and (3) the availability of effective
control measures. In all three respects the SAT
and Eurasian lineages of FMD viruses differ
significantly.
Differences between the two FMD virus lineages
were first remarked upon in 1932 by Prof P.J.
du Toit, former Director of Onderstepoort
Veterinary Research and Dean of the Faculty of
Veterinary Science, University of Pretoria. Prof
du Toit was asked by the British Government
to investigate the first outbreak of FMD in what
is now south-eastern Zimbabwe following the
Great Rinderpest Pandemic of 1896-1904. That
pandemic decimated both cattle and buffalo
populations of the subcontinent. Although at
that time the role of buffalo, or the existence of
different FMD virus types was unknown, Prof
du Toit concluded that the FMD he investigated
in Zimbabwe was ‘different’ from the FMD that
was then widespread in Europe. This difference
related mainly to the slow and inefficient spread
of the disease between infected and susceptible
cattle herds in close contact with each other on
Nuanetsi Ranch, i.e. in contrast to the rapidly
spreading nature of the disease in Europe.
Apart from the unique association between SAT
viruses and African buffalo and the inefficient
transmission of these viruses between infected
and susceptible cattle, there are other important
differences between the two viral lineages. These
include (1) the tendency for SAT outbreaks in
cattle to cause mild or unapparent disease in only
a small proportion of the exposed population;
often below 1% and (2) the differing importance of
carrier animals of various species in maintaining
the infection (where current indications are
that although carrier buffalo are important in
maintaining SAT viruses within breeding herds
of buffalo, cattle are not involved in carrier
transmission). However, the ‘carrier’ status of
different ruminant species is a contentious issue,
unresolved by over 100 years of investigation. (3)
The third difference relates to the wider range
of virus variants and lack of identified subtypes
within SAT viruses that, in contrast to the Eurasia
types, makes the manufacture of vaccines that
‘match’ the wide variety of viruses present in the
field difficult.
Relationship between FMD viruses
and wildlife
Figure 2 summarises what could be referred to as
the ‘Southern African FMD triangle’ involving SAT
viruses maintained primarily by African buffalo
but also transmissible to other cloven-hoofed
wildlife species and domestic livestock.
Fig 2. Spread of FMD between African wildlife and livestock in Southern Africa
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