Tuesday, 5 July 2011

Rinderpest erradication

I'm often suprised when talking to guides about how few know of the great African rinderpest epidemic of the late 19th Century, as it has had a huge impact on the wildlife we see around us today. I'm prompted to write of it now for two reasons - the first being news I missed whilst busy training in Tarangire at the end of May and have only now noticed: on 25th May this year, the Food and Agriculture Organisation (FAO) announced the global erradication of rinderpest. This is surely something to be celebrated, as the first global erradication of any animal disease. And as we'll see in a moment, what a good disease to erradicate! The second reason is somewhat less pleasant, as I hear there's a measles outbreak here in Arusha at the moment. Why should this prompt me to write abour rinderpest? Well, evidence suggests that measles is actually a mutated form of the rinderpest virus that affects people. In fact, it seems most likely it evolved during the 11th or 12th century during one of the periodic rinderpest epidemics in Europe at that time, showing once again how nasty diseases have a habit of jumping across species boundaries when they get very common.

If you're wondering why I'm interested in cattle diseases at all, you've not heard about the African rinderpest epidemic, and of the impact of the disease and its control on wildlife. So let's start back in 1887, when the Italians were busy trying to colonise Ethiopia (afterall, the rest of Europe had colonies, why shouldn't they?). It seems as though some time early in the year they imported cattle from Asia that had the disease - whether as a deliberate act of biological warfare or accidently within their own supplies we're not certain (there's apparently no evidence to support the often heard claim of biological warfare), but whatever the reason it didn't take long for the disease to spread. Within they year up to 90% of Ethiopian cattle died, and at least 30% of the human population too (some estimates put it up to 60%). By 1897, after a short pause at the Zambesi and a couple of southern cattle fences, the disease had reached Cape Town, destroying 60-90% of Africa's cattle along the way. (You can read more about the human cost of this here if you want.)

Cattle aren't the only animals to suffer from rinderpest though - most ruminants were susceptible, some even more than cattle with up to 90% mortality of wildebeest and buffalo. Descriptions from travellers in Serengeti during 1898 suggest there were huge mortalities among the wildebeest, with the plains covered with carcasses. And for the next 60 years the numbers of animals in the Serengeti - Mara ecosystem were vastly reduced, held constantly in check by disease: in 1963 there were an estimated 250,000 wildebeest in the ecosystem (compared with 1.4million today) and immediately post disease outbreak possibly as few as a few tens of thousands of  individuals. The key change allowing the populations to recover was the erradication of rinderpest in the cattle around the park, following a large-scale vaccination programme. In fact, across most of British colonised East Africa at the time a plan was formed to erradicate wildlife from the area as a way of controlling rinderpest, but the colonial administration decided that whilst they could manage to shoot everything in most places Tsavo (in Kenya) and Serengeti/Mara were just too big, so around these areas they'd institute a 'cordon sanitaire' where cattle would forever have to be immunised, isolating the disease within the parks. This cordon was completed in the 1950s and by 1963 rinderpest died out of the wildlife population - the disease was so effective at killing wildlife that it couldn't actually be sustained within the population and had only be maintained by continual re-infection from cattle in the surrounding areas.
There are a lot of Wildebeest in Serengeti today - the view from Naabi hill, Jan 2011

Which led to a six-fold increase in wildebeest populations from 1963 to 1977 (and other increases in buffalo, etc), with a huge increase in the amount of grass being consumed by animals. (Read more about it here.) Of course, eating all the grass had a huge impact on how much fuel there was to carry fire in the ecosystem, and the frequency of fire started to decline in the 1970s. And as we know, fire has massive impacts in the savannah and it's decline is, perhaps, responsible for the return of acacia woodlands across much of Serengeti from the 1980s. (And so many visitors think of Serengeti as an ecosystem in the same state as it was thousands of years ago! Unchanging Africa is a myth...) But that's also a complicated story we'll deal with another time - for now, let's be glad there's no more rinderpest anywhere, let alone in Serengeti.

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