Dr Mary-Louise Penrith, a veterinary consultant
In eastern and southern Africa, African swine fever (ASF) has been present for a very long time, and this is not a matter of very great interest in the wider world. The disease appeared in the international spotlight for the first time in 1960, when an introduction of the virus into Portugal, probably from Angola, failed to be controlled and the disease spread into Spain. Both of these countries had very large pig industries, unlike Africa, and for the first time the devastating effects of ASF were appreciated, as well as how difficult it can be to control it. During the 1970’s and 80’s quite a number of countries had the opportunity to experience it at first hand, including Belgium, France, Italy, Malta, Cuba, Haiti, Brazil, and (as has only emerged recently) Russia! Eradication was extremely expensive and the disease persists on the Italian island of Sardinia.
Nevertheless, and in spite of a pandemic in West Africa that started in 1996, international interest in ASF waned after the Iberian Peninsula was declared free of ASF in 1994. In fact, a request for funds to try to bring the West African pandemic under control was turned down by US donors on the grounds that it did not pose a threat to the USA! Now, in 2010, there is deep concern that ASF could indeed reach North America. What has changed?
The international spotlight focused on ASF again with the appearance of African swine fever in the Republic of Georgia in 2007. This was followed by rapid spread to all its neighbours except Turkey, where there is no significant pig production.
By early 2008 outbreaks had been reported from Armenia, Azerbaijan, and Russia. Azerbaijan could eradicate it quickly because only a single village was affected, but Armenia reported an outbreak as recently as March 2010, Russia has been suffering rolling outbreaks since it first was diagnosed there in wild boars in Novem-ber 2007.
The presence of ASF in that region has sounded alarm bells in many parts of the world, and in March 2010 a workshop was hosted in Chicago, USA by the Animal Infectious Disease Initiative of the College of Veterinary Medicine, University of Illinois. The title of the workshop was African Swine Fever: Prospects for Control of a Re-emerging Transboundary Disease.
There were 35 invited participants consisting of experts on ASF, experts on control of other infectious diseases, representatives of the pig industry in the USA, and delegates from Armenia, Russia, Kazakhstan and Ukraine. Ukraine and Kazakhstan have not yet experienced ASF yet but there was an outbreak in Russia five km from the Ukrainian border and an outbreak not far from the border of Kazakhstan in 2008, so they are on high alert. The ASF experts were mainly laboratory researchers, many of them not vets, and the workshop revealed an interesting and rather alarming chasm that is developing between Laboratory ASF and Field ASF, but that is another story.
I was invited to present the African context of the disease, but although everyone appeared to thoroughly enjoy the warthogs, the tampans and the colourful peasant pig farmers, as well as our very well protected commercial farms in Limpopo, it is very clear that ASF in Africa is not what the pig-producing world at large is worried about. Of course they should be – Georgia certainly got it from Africa, almost certainly via galley waste, but the fact that diseases are introduced into countries almost exclusively via illegal means is sadly, and dangerously, often ignored, perhaps because nobody knows what to do about it.
The great fear is that ASF will get into China – or that in spite of all reassurances it may be there already – and then it could spread like wildfire all over the world. The other fear is that Russia will not manage to control it and it will eventually spread into Eastern and subsequently Western Europe and perhaps to America. Since the classical swine fever outbreaks in The Netherlands in 1997, UK in 2001 and South Africa in 2005 and the Type O foot and mouth disease in South Africa in 2000 and in UK in 2001/2 were caused by Asian viruses, the nervousness may be justified, although USA was not affected.
The prospects for control of ASF in Russia do not look particularly rosy. The Russian delegate indicated that they are chasing after the disease with too few resources because the government is reluctant to invest in controlling non-zoonotic diseases. There is also the problem that where it is all happening the people are not particularly friendly towards the central government or likely to cooperate with it. Also, quite a number of the cases have been in wild boars.
It is unknown whether infection has become established in wild boar populations or whether the cases have been due to contact with infected domestic pigs or their remains, but it is a concern because in Sardinia ASF is maintained in the very large wild boar population. They are not carriers and they die of disease as readily as domestic pigs do, but there are enough of them to keep the infection going indefinitely, and the same thing could theoretically happen in Russia. The fear of a focus of ASF that is considerably closer to Europe and North America than Africa has driven the European Union and the USA to consider preparing for an invasion.
The lack of a vaccine limits the options for controlling an outbreak of ASF. The conventional approach is, as with most diseases in industrialised countries, to declare an infected area, impose quarantine and a movement ban, and stamp out all the pigs in the infected area with destruction of the carcasses by deep burial or burning.
It is an effective way of controlling outbreaks of animal diseases but both its success and its practicality can be limited by factors related to the production system, the size of the pig population that will have to be eliminated, and the resources available to undertake the operation. It has always worked well in eastern and southern African countries like South Africa, Botswana and Namibia where the source of infection has been the warthog/tampan cycle and usually only a single, quite small piggery is affected.
However, in most countries in Africa and in all cases outside Africa outbreaks result from the movement of infected pigs or pork, which results in rapid spread and usually in multiple piggeries having the disease. In developing countries the difficulty of successfully stamping out ASF has been amply demonstrated. The prerequisites for success are early diagnosis, so that as few pigs as possible need to be eliminated and disposed of, and sufficient resources to be able to act swiftly to do the stamping out before people and pigs can take avoiding action.
Lack of compensation of owners of healthy pigs slaughtered has been one of the key factors in the failure of stamping out operations, however many other factors like inability to prevent movement of pigs and the sheer desperation of poor people who will do anything to get some money for their remaining pigs, which are probably incubating ASF, and to sell the meat of the pigs that die, also play a role in the failure of the measures.
The situation is, of course, quite different in wealthy, industrialised countries where market-related compensation would not be impossible, the producers are educated, and there is a strong veterinary service that can enforce control measures and where necessary call in the assistance of other well-organised forces. However, apart from the fact that poverty is not the only driver of attempts to avoid economic losses – being comfortably off doesn’t make a person eager to lose money – there are many other factors that dictate that whether or not stamping out is accepted to be Plan A in the event of an outbreak, alternative plans must be in place and might even seem a better first option.
One of the main complicating factors is the sheer number of pigs that might need to be killed and disposed of. The pig farming sector is highly industrialised in the USA and Western Europe and ASF is a disease that would certainly be noticed immediately in a large commercial farm, but early diagnosis is nevertheless not guaranteed. Smallholder pig farmers are widespread in Eastern Europe, including countries recently incorporated into the EU, and are also numerous in parts of Western Europe, as well as in North America. Many of these farms have limited or no bio-security, and swill feeding in spite of bans in the EU is not a thing of the past. It is still legal in several American states.
Additionally, the USA has a large population of feral pigs. It is believed that the most likely entry point for ASF would be through swill-fed or scavenging pigs, and since these pigs are not under constant veterinary supervision the disease could spread quite a lot before perhaps striking several commercial operations in different areas simultaneously. The large number of animals that had to be killed and disposed of in both the 1997 classical swine fever outbreak in The Netherlands and in the 2001 outbreaks of foot and mouth disease (and classical swine fever) in the United Kingdom, not only caused public outrage but posed an almost insurmountable challenge in terms of getting rid of the carcasses.
The worst tragedy was the large number of healthy animals that had to be killed. In particular, in the classical swine fever outbreak in The Netherlands it is reported that of the eleven million pigs killed, nine million had to be killed for welfare reasons only because of the massive overcrowding that resulted from the movement standstill.
These pigs were perfectly healthy but could not be offered for human consumption because they could not be moved to abattoirs but had to be slaughtered on the farms. In the USA, where every day there are more than half a million pigs on the road, the chaos that would result from a standstill can only be imagined. Industry representatives at the workshop were adamant that in the event of an outbreak of ASF the approach would have to be containment rather than a lockdown, and that as far as possible normal trade in pigs would need to be facilitated.
The good biosecurity protocols in place on the high level farms make the risk of introduction of ASF very low. Because it is not an air- or waterborne disease, the risk of introducing it into a farm that feeds commercial rations, has strict biosecurity in place to exclude transmission by fomites (contaminated footwear or other objects) and safe protocols for sourcing and quarantining new introductions to the herd becomes negligible. Additionally, there is already strong surveillance in the USA for classical swine fever that targets swill-fed pigs, and plans are that tests should be in place to detect ASF in these operations as well. This, incidentally, is surveillance for the virus and not just serological testing for antibodies, because in both classical and African swine fever by the time antibodies can be detected, it is too darned late!
The laboratory scientists at the workshop updated us on the state of diagnostic tests and vaccine development. In terms of diagnostic tests, while there are very effective and possibly excessively sensitive laboratory tests available, there was agreement that for surveillance of sick pigs it would be very advantageous to have a test panel that could be used to detect not only ASF, but also the most important diseases that can be confused with ASF. This would not only allow simultaneous testing for both swine fevers, but would detect treatable diseases like salmonellosis and erysipelas so that the farmers would be keen to cooperate.
The idea of focusing on pen-side tests was discussed at length and finally rejected, because it was felt that those developed so far for various diseases do have problems in terms of false positive as well as false negative results that are compounded by the fact that they are not necessarily used by people who can interpret the results correctly, and they have to be confirmed in the laboratory in any case.
The test should also be of a “safe” type that could be used in ordinary laboratories that do not have the required level of biosecurity to handle live exotic viruses. Currently samples suspect for ASF in the USA could only be tested at the Foreign Animal Diseases Diagnostic Laboratory at Plum Island in New York.
As far as a vaccine is concerned, there does not seem to be any prospect of having one in the short term and perhaps not even in the medium term, but everyone agreed that efforts to develop one should continue if at all possible. Interestingly, the representatives from developing countries or regions (Africa, Armenia and Russia in particular) were more hesitant about whether they would use a vaccine than the representatives of the US pork industry.
The main reason we felt uncertain about it was affordability and whether it would work under the difficult conditions where it would be most needed, i.e. regions where the cold chain cannot always be guaranteed.
Is there a message for the South African pork industry in all of this? I believe there is. The possibility of ASF sweeping through the SA pig populations seems extremely unlikely, as indeed the likelihood of it reaching the USA is very low indeed. However, we have seen that unexpected disease events can happen, and they can involve our pigs. While reasonable measures to avoid importing diseases through legal imports can and should be in place, these measures would almost certainly not have prevented the introduction of PRRS, classical swine fever or Type O foot and mouth disease. Access of these and other diseases to commercial pigs is preventable by adequate on-farm biosecurity measures.
These have the advantage of protecting the pigs against a whole array of diseases that might otherwise reduce productivity, and of reducing the costs incurred for medication as well. It makes sense to have these measures rigorously in place. It also makes sense for the industry to work with the veterinary authorities to include in national contingency plans provision that farmers who implement biosecurity protocols and are farming safely can continue to trade if there is a disease outbreak that affects pigs, according to protocols that ensure that the trade will be safe.