By Dr Mary Louise Penrith
The West African ASF pandemic started, like all pandemics, fairly quietly. Pigs started dying in unusual numbers in the city of Abidjan, the main port of Côte d’Ivoire (CIV), mainly in a poor quarter of the city where pigs were kept in backyards and fed on swill, collected mainly from garbage skips around the city.
Some of the pig owners sought veterinary help, and when treatment with antibiotics made no difference, the horrible suspicion arose that this could be African swine fever, which had never previously occurred in CIV or in any of its neighbours. The diagnosis was confirmed in April 1996, and the government, with help from FAO, started trying to eradicate the outbreak.
Unfortunately quite a few pig owners, concerned that the government would kill all their pigs without compensation or thinking the country air would be healthier for the pigs, moved their pigs from the city to villages deep in the countryside, and reports of pig deaths started to come in from all over the southern part of the country. Getting control measures in place proved difficult. For example, a veterinary presence was only permitted at the country’s fairly numerous police roadblocks at the end of October.
The last outbreaks were reported in September! The government and its advisers breathed a sigh of relief, but pig farming in the Greater Abidjan area had been devastated. By that time all 120 000 pigs in the Greater Abidjan area, one third of the entire pig population of CIV, had either died or been culled, with compensation for culled pigs being set at about one third of market price. In the small but vibrant commercial sector, a number of modern farms, in spite of being isolated, never having been infected and having good biosecurity, were depopulated in the interests of ensuring that there were no pigs in the prescribed radius, causing considerable financial and emotional distress to the owners.
These included a woman who had recently and at great expense imported several excellent sows from France, only to have them destroyed, with the low compensation giving her little comfort.
Relief was short-lived. In September 1997 ASF outbreaks occurred in Benin for the first time, followed rapidly by its neighbours Togo and Nigeria. Benin and Togo are both small countries with relatively large pig populations; Nigeria’s pig population exceeds 7 million, concentrated mainly in the south of the country. In all three countries spread was rapid and eradication measures, applied when the epidemics were already well established, failed. In October 2000 ASF was diagnosed for the first time in Ghana, in the city of Ho, which is very close to the border with Togo and the people on either side are related and keep pigs. By the time it was discovered it had spread to the large port city of Tema and the capital, Accra. Ghana, also with assistance from FAO, managed to eradicate ASF in a relatively short time without culling vast numbers of pigs and with prompt compensation at market rates when pigs were culled, enabled by a one-off World Bank loan.
However, the open border with Togo proved too much of a temptation to traders, and Ghana has since joined the ranks of countries that are considered to be endemically infected. Burkina Faso, which shares its southern border with CIV, Ghana, Togo, Benin, and Nigeria and has a population of around 2 million pigs, experienced its first outbreaks in 2002, and remains endemically infected. During the period between 1996 and 2002 Senegal, Gambia and the Cape Verde islands, considered to have been infected at least since the 1970’s and perhaps earlier, when ASF reached Europe, also experienced increased ASF activity, and FAO put in place a regional technical cooperation project, but CIV is the only country that eradicated the infection and has remained free.
Why did the pandemic happen?
Pig keeping has a very long history in West Africa. A recent publication on the history of domestic pigs in Africa identified ancient sites where pigs were kept in West Africa that appear to have preceded Portuguese introduction of Iberian pigs when they colonised West African countries in the 15th century.
In East and Southern Africa, where the number of domestic pigs is lower than in West Africa, ASF has been known and researched for almost a century. The first official reports of ASF in West Africa were from Senegal in 1978 but rumours about ASF in Senegal, Guinea Bissau and Cape Verde began to circulate in 1959, and it seemed likely that they could have become infected via Europe, since ASF had been introduced into Portugal, probably from Angola, in 1957.
The first introduction into Senegal may have been from Cape Verde, as there is considerable traffic between the two countries. Although warthogs occur in West Africa, limited surveys failed to find any evidence of infection with ASF, and also failed to find the soft ticks, or tampans, which are necessary to transmit the disease from warthogs to domestic pigs. Only after ASF became widespread in Nigeria were individual wild pigs (a warthog and a bushpig) found to have antibodies against ASF virus, and this has been ascribed to spill over from infected domestic pigs. It can therefore be assumed that the ASF virus that started the pandemic was introduced via infected domestic pigs or, more likely, infected pork, as happened in Europe in the last century and recently in the Caucasus.
One probable contributing factor is that the number of pigs in West Africa has been growing markedly since 1980 (Figure 1). A similar growth pattern has occurred in East Africa, with Central Africa showing more modest growth and pig numbers in Southern Africa having remained almost stable.
Figure 2 shows that the number of countries reporting ASF has increased over time but that there was a more marked increased during the 90s, mainly due to the West African pandemic. The association between an increase in pigs and ASF is supported by the fact that Cameroon (Central Africa) experienced ASF for the first time in 1981 after pig numbers had doubled in the preceding few years, mainly due to a growing commercial industry around the major cities of Douala and Yaoundé. The bottom line is that more pigs mean more movement, more feed, more trade and therefore a higher risk of introduction of ASF.
Although it was triumphantly announced in CIV that the outbreak originated from a garbage skip in a wealthy suburb whose inhabitants ate imported food because one of the affected owners collected his swill there, obviously no “smoking pork” could be found a month or two after the event. In fact it is very unusual to be able to pinpoint the start of an epidemic; in both Ghana and CIV investigations indicated that outbreaks had been occurring for some time before the first case was diagnosed.
The ability of countries in West Africa to eradicate ASF depended on the size and distribution of the pig population. Free-ranging pigs are the norm in rural areas throughout the region. They may be housed seasonally to prevent them from damaging the crops. In the larger towns and cities, large numbers of pigs are kept in smallholder backyard operations, and there are also commercial farms, usually with no more than 100 – 500 pigs. In CIV, the in-contact free-ranging populations are relatively small because the villages or clusters of villages are usually separated from neighbours by quite a considerable distance, giving the outbreak a chance to burn out, which it will do if there are no longer any pigs to infect. In Benin, Togo, and large parts of Nigeria, both the human and the pig populations are dense, so that there is a high level of contact between pigs over a wide area, aided by the fact that trade largely involves speculators who go from farm to farm buying up pigs to sell at a market or to other farmers along the way.
Paradoxically, although free-ranging pigs with a high level of contact with other pigs can be crucial for maintaining ASF and allowing it to become endemic, outbreaks seldom if ever start in free-ranging pigs in rural areas, except where warthogs are involved. Pigs that range freely through cities scavenging on garbage are another matter, of course, particularly if they have access to landfills where port or airport swill might be disposed of!
There is very little doubt that the introduction of ASF into a previously uninfected country without infected neighbours sharing its borders is via infected swill, usually of illegal origin (e.g. port waste), being fed to backyard or even commercial pigs. Once borders are shared with one or more infected countries, the most likely source of infection in West Africa is live pigs. In addition to the mentioned continuous populations, price differentials between countries may make cross-border trade in pigs more attractive than local trade. Much if not all of this trade takes place without the benefit of animal health inspection and certification; it is not legal but the risk of being caught and punished is extremely low.
It is unlikely that ASF spread directly from CIV to Benin, and the source remains unknown, but it appears that there was an increased circulation of the ASF virus in the region from 1996 onward. CIV’s neighbours all apparently escaped infection in 1996. There was a campaign to increase awareness on the Ghanaian-CIV border, and other favourable factors were a lack of pigs close to the border in both countries and the fact that the higher value of the West African franc over the Ghanaian cedi made pigs from CIV too expensive for the Ghanaian market. CIV’s neighbours to the west were less at risk: Guinea is largely a Muslim country with a very small pig population, and Liberia was in the midst of a civil war that had caused most of the population close to the CIV border to flee across it and either settle in CIV or continue on to Ghana. Burkina Faso was protected by the fact that ASF did not spread to the north of CIV, which is predominantly Muslim and therefore the pig population is fairly sparse and in general reasonably well controlled.
Once Benin became infected, infection of Togo and Nigeria was almost inevitable, and once Togo was infected, Ghana and Burkina Faso were likely to be infected as well owing, to a continuous population across the border with Ghana and a well-established trade route between Togo and Burkina Faso. Usually pigs fetch higher prices in Benin than in Togo, but once ASF was decimating pigs in Benin and people were desperate to sell their pigs before they died or the government tried to kill them, the price dropped sharply and the trade direction reversed. The tendency to sell pigs once the first victims in a herd have died contributes greatly to the spread of ASF, as most of the pigs that are sold will already be incubating the disease and will be shedding virus before the clinical disease becomes apparent. Furthermore, sick pigs and meat from dead pigs may be sold, as the entire trade is informal and takes place without the benefit of meat inspection.
One of the things that we learned from the West African pandemic is just how devastating ASF can be, even in the absence of a highly industrialised pig industry. Although pig numbers in most of the affected countries have recovered and even increased, there is no doubt that a great deal of suffering was experienced by poor people who kept some pigs in order to be able to survive, and that the ongoing outbreaks are certainly not helpful to efforts to supply the population with more protein at affordable prices and to reduce poverty.
Another thing we learned was that simple biosecurity measures are sufficient to prevent ASF if they are consistently and rigorously applied. In Benin and Ghana, at least, once the commercial farmers understood what they needed to do to keep ASF out of their farms, very few of them lost pigs, and their biggest problem was one of pigs piling up on their farms because they were not allowed to move them to an abattoir for slaughter.
This was resolved in Ghana by designating certain slaughter facilities, cold stores and retail outlets as veterinary approved and moving pigs only with a permit or an escort from approved farms. This had to be done to prevent an influx of probably infected pork from Togo to meet the demand over Christmas, and it had no untoward results because the farmers involved were highly responsible and had been involved in the decision-making from the outset.
As a general rule we found it was better to allow people to move pigs from healthy, uninfected herds to abattoirs to reduce the size of the pig population at risk and also to reduce the rampant law-breaking that is the normal response to a total ban on sales and can result in increased spread of the disease. We also found that involving the farmers and other pig industry operatives was helpful in controlling the law-breaking as they had a vested interest in stopping spread of the disease by ignorant people looking for an opportunity to make a quick profit.
Finally, it became clear that we need to take a long, hard look at the way pigs are marketed in sub-Saharan Africa, because not only are some of the practices risky for diseases, most of the pig farmers are not realising the prices that they should get for their product because of lack of information, lack of infrastructure and general lack of organisation. Once farmers are assured of a good price, they will be prepared to invest more in their pigs.
If the West African ASF pandemic and other outbreaks have shown us anything apart from tragedy and certain things that need to change, it is that most of the people who farm pigs, whether they have a pair in the backyard or a large commercial herd, are doing it because they want to, and in spite of the adversity most of the farmers who lost all their pigs were determined to start again and do it better than before. In fact, it shows that you can’t keep a good pig farmer down!