By Dr Mary-Louise Penrith, a veterinary consultant
African swine fever (ASF) is increasingly being recognised as an emerging infectious disease. Its importance was first realised when it became established in Portugal and Spain in the late 1950’s and the devastation that it could cause in highly developed commercial pig farms was demonstrated. A positive effect of this was that a great deal of research was initiated, which for example demonstrated that soft ticks, or tampans, that were present in the pig sties in the Iberian Peninsula were efficient at maintaining and transmitting the virus, just like their African counterparts that live in warthog burrows.There was, however, a negative effect on the ASF situation on the African continent, because for some time the focus shifted away from Africa. Although research on the sylvatic cycle in southern and eastern Africa continued, ASF events in domestic pigs in Africa didn’t excite the same interest as they did elsewhere, perhaps because pig production was on a much smaller scale than in Western Europe.
It seemed as if ASF was comparatively easy to control in Africa – just keep the pigs and the warthogs apart. Only about five percent of the world’s pigs are produced on the African continent, according to official statistics of the Food & Agriculture Organisation of the United Nations (FAO), so perhaps the relative lack of concern was understandable.
However, pig production in sub-Saharan Africa was growing, mainly to feed rapidly expanding urban populations, and quite a lot of this growth was happening on smallholdings and in backyards around the cities, where poor people saw an opportunity to improve their income by farming a species that needed very little land and ate just about anything. Pigs in traditional African rural free-range systems are certainly in danger of ASF, particularly in the parts of southern and eastern Africa where the warthogs and their tampans are infected, but pigs in backyards may be at even greater risk.
Because they can no longer scavenge for their own food, their owners do the scavenging, and very often feed the pigs on leftover food, or swill, from restaurants, hotels, and any other convenient source, as long as it is very cheap or even sometimes comes free if the owners have access to garbage skips and dumps. In 1981 Cameroon, which had never previously experienced ASF, had a massive outbreak that halved its domestic pig population in a very short space of time. Perusal of the FAO statistics indicates that pig production had almost doubled in the few years before the outbreak occurred.
In spite of efforts to eradicate it, ASF became endemic in Cameroon. This raised the level of interest in ASF in Africa somewhat, particularly as other countries in West Africa (Senegal and Nigeria) had also experienced outbreaks in the preceding years. Since the virus was the same type as had infected Europe, it was even speculated that it may have been introduced back into Africa.
Some research during the late 1970s and the 1980s revealed that West African warthogs were not infected with ASF virus and there were no tampans to maintain the virus in southern Senegal or in Cameroon, and also that there was a population of free-ranging domestic pigs in south-western Malawi that had little or no contact with warthogs but in which outbreaks of ASF occurred regularly. In this case tampans in pig shelters were found to be involved.
However, in the same period, ASF crossed the Atlantic Ocean to infect the Caribbean islands of Cuba and Hispaniola (Haiti and Dominican Republic), as well as Brazil, and also affected a number of western European countries including The Netherlands, Belgium, France, Malta, and Italy, making what happened in Africa almost irrelevant.
Eradication in most cases was fairly rapid although expensive, but proved impossible in the Italian island of Sardinia, where to this day the disease is maintained without the assistance of warthogs or tampans in populations of free-ranging pigs, with occasional involvement of the large population of European wild boars as well. The failure to eradicate this blot on the otherwise ASF-free European Union is blamed mainly on Sardinian pig producers, who are said to be strongly averse to obeying the law.
Spain and Portugal eventually managed to eradicate ASF in 1993/1994, and, apart from Sardinia, it seemed that the European chapter on ASF was closed. At the same time, a new chapter opened in Africa. It began with an outbreak that swept through the southern provinces of Mozambique in 1994.
Although ASF occurred frequently in the northern part of the country, there had never been an outbreak south of the Save River before, with the result that there was a flourishing pig industry around the city of Maputo that looked set for a bright future when the civil war ended in 1992. This undoubtedly encouraged an influx of pigs from further north, and it appeared that the first outbreaks occurred in traditional pig farming areas in Inhambane, from which pigs are often sourced for the Maputo market. In the same year, Kenya reported the first outbreak in 30 years, and, like the southern Mozambique outbreaks, it was not associated with warthogs but with movement of pigs from close to the border with Uganda.
Since the situation was unusual, the FAO offered technical support to both countries to improve diagnosis and try to bring the situation under control, although ASF was not at the time considered by the FAO to be of great importance.
However, in 1996 ASF jumped to prominence in West Africa with a massive outbreak in Côte d’Ivoire, never previously infected, and in the next five years the FAO was involved in projects to control ASF in Côte d’Ivoire, Benin, Togo, Nigeria, Cabo Verde, Ghana, and Gambia in West Africa, as well as in Tanzania and the first-time infected island of Madagascar.
There were also devastating outbreaks in Zambia and in Burkina Faso. None of these countries had highly developed commercial pig industries, but it would be impossible to calculate the losses incurred by local pig producers, since it must be measured in terms of children not educated and a major decrease in quality of life for numerous families who lost the pigs that provided their most reliable source of disposable income.
Ever since, many African countries, including Kenya and Mozambique, have registered regular outbreaks of ASF. In 2001 the West African countries requested international assistance for the control of ASF and a workshop was held under the auspices of the FAO and the World Organisation for Animal Health (OIE) in Togo in November 2001. International donor organisations, however, failed to fund the proposals on the grounds that ASF was by and large an African problem and did not pose a threat to the rest of the world, since export of pigs and their products to the rest of the world is minimal, and the little that is exported comes from reliably ASF-free sources.
In 2007 this view proved wrong. Shock waves were registered as ASF was confirmed in the Republic of Georgia, and although the international efforts mounted by western countries to assist with control far surpassed anything done in Africa, it was all to no avail. Not only was the pig population in Georgia decimated, but the disease rapidly spread to neighbouring Armenia, where there are few pigs left in the northern regions that share a border with Georgia, and outbreaks have occurred throughout the tiny country.
Pork is a sought-after delicacy in both countries, where, as in Africa, many poor people in villages rely on their pigs to keep their families fed during the severe winters that especially Armenia experiences. Since both countries are officially part of the Asian continent, the event brings the number of continents that are or have been infected by ASF to four.
Two other neighbours were also infected as well. Azerbaijan experienced ASF in January 2008, but as the outbreak was confined to a Christian village whose inhabitants are of Georgian origin, it was rather easily contained, most of the inhabitants of Azerbaijan being Muslims who do not keep pigs. More worryingly, the other infected neighbour is Russia, and a cause for deep concern is that ASF was first registered in wild boars that died in Chechnya close to the Georgian border.
Although neither wild boars nor domestic pigs become long term carriers of ASF on the rare occasions when they do recover from infection, large enough continuous populations of pigs (wild or domestic) can maintain virus circulation indefinitely, provided they breed fast enough to ensure a never ending supply of fresh pigs to infect, so that the outbreak does not burn out.
It was at the time hoped that there would not be serious implications for Russian domestic pigs, because the populations of most of the Russian republics that share Georgia’s border are predominantly Muslim. However, there are clearly enough pigs for this not to be the case, because ASF has spread to Ingushetia and North Ossetia, both republics within the Russian Federation, as well.
There was also a spectacular leap of more than 1 000 km to the Orenburg province of Russia, which borders on Kazakhstan, probably via infected pork, but cases in wild boars were registered there as well. The North Ossetian outbreaks are likely linked to movement of people and probably pork and pigs from the breakaway Georgian province of South Ossetia during its five day Russian-backed war with Georgia in July 2008.
Molecular genetic typing at the World Reference Centre (Pirbright, UK) of the virus that infected Georgia left no doubt as to its African origin. It is a virus that is currently very active in Mozambique and Madagascar (it also infected Mauritius in October 2007), and could not have originated anywhere else. It is therefore extremely short-sighted for anyone to think that ASF activity in Africa is not a threat to pig industries wherever they may be.
Moreover, there is absolutely no evidence to suggest that legal exports from Africa have anything to do with introducing ASF. The most likely source of the virus, both in the Caucasus and Mauritius, is galley waste from ships that were most likely provisioned with supplies that included infected pork.
This is a major cause for concern, as there is no doubt that infected pigs will enter the food chain during outbreaks, since once pigs start to die, the remaining pigs of slaughter age will be shipped hastily to the abattoir to prevent further financial losses, and some of them will certainly be in the incubation stage of the disease.
The only possible and fair solution to the problem is to provide pig farmers throughout Africa with the support and training that they need to help them to farm their pigs safely. People who need to generate income by keeping pigs will do so whether they are supported or not, even if their activities are declared to be illegal. The constructive approach, which is currently being applied in Armenia and also in Mozambique, is to ensure that people who produce pigs understand the very basic and simple biosecurity measures that must be applied to prevent ASF.
The more pigs an owner has, the more sophisticated the measures will be, but because ASF is a directly transmitted disease the basic rules are very simple, and owners who apply them can prevent infection successfully. In the Caucasus we have had to discredit the belief that ASF was introduced by little pieces of infected meat dropped to the pigs by passing crows, or that it was flowing along all the rivers into which people had dumped carcasses. These are convenient excuses, but fortunately that is not what happens, or there would likely not be pig left alive anywhere!