Only two infectious diseases have ever been actively eradicated by humans. One is very well known – the once-deadly smallpox – the other is the less renowned rinderpest, once the cause of fever and fatal dehydration in cattle. Now, efforts are underway to make peste de petits ruminants (PPR) – prevalent in parts of Africa, Asia and the Middle East – the third disease on that list.
Like rinderpest, PPR doesn't affect humans, but can be socially and economically crippling to people in developing countries due to the way it infects ruminants, such as sheep and goats. The virus is extremely contagious and can result in near 100 per cent fatalities. Consequentially, the Food and Agriculture Organization of the United Nations (FAO) has pledged to wipe out the disease by 2030, mainly through the use of mass vaccination campaigns.
‘As with rinderpest, we have a very effective vaccine for PPR,’ explains Dr Guillaume Fournié, a senior research fellow at the Royal Veterinary College (RVC). ‘Once an animal is vaccinated, it is protected for its lifetime against any lineage of the virus. The problem is that there are a far greater number of sheep and goats than cattle in the world. Sheep and goats have a high turnover, mainly because these animals are culled more rapidly. This means that if you vaccinate all the animals, then come back a year later, the coverage (the number of animals which are immune) will have really dropped because lots of animals have been culled, replaced by new, young animals which are susceptible to the infection.’ The relatively lower economic value of each animal also makes it harder to raise investment to fund vaccination campaigns.
A new strategy developed by Fournié and researchers at the RVC lays out a plan for focusing efforts on eradication in especially endemic regions, as opposed to a broad global vaccination campaign, which can be expensive and logistically challenging. Their results show that by focusing on so-called ‘viral reservoirs’ in countries such as Ethiopia (heavily-impacted by PPR), the spread of the disease can be most effectively suppressed.
‘The disease seems to transmit much more in pastoral production areas, compared to sedentary areas,’ explains Fournié, ‘which makes some sense, because it’s a disease which is mainly transmitted by direct contact between animals. So these pastoral areas really need to be targeted by vaccination efforts.’
While cases of PPR have recently been identified in Bulgaria, Fournié insists this is purely due to a very close proximity to Turkey – another country often afflicted by PPR – and that as long as there isn't direct contact between animals, there is a very small chance of the disease ever finding its way across Europe.
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