African Swine Fever: A re-emerging viral disease threatening the pig industry

Dr Mangsatabam Norjit Singh *

African Swine Fever (ASF) is a highly contagious, devastating and deadly viral disease of domestic and wild pigs, whose mortality rate can reach 100% in its acute form. The disease is caused by African Swine Fever Virus (ASFV). The virus is highly resistant in the environment and it can survive on clothes, boots, wheels and other materials for many days. It can also survive in various pork products, such as ham, sausages or bacon.

Therefore, human behaviours can play an important role in spreading this pig disease if adequate measures are not taken. The outbreaks have serious economic impact, particularly on farmers whose livelihood depends on pig farming and for consumers who are faced with the brunt of increasing pork prices.Pork meat is one of the primary sources of animal proteins accounting for more than 35% of the global meat intake.

Hence, this disease poses a serious problem for food security worldwide.Presently,the disease is affecting the pig population in several regions of the world and with no commercial vaccine available;ASF is not only affecting the animal health and welfare but also has detrimental impacts on biodiversity and the livelihoods of farmers.

It has become a major crisis for the pork industry in recent years due to massive losses in pig populations and drastic economic consequences. ASF has been listed into the category as “notifiable disease” by the World Organization for Animal Health (OIE).

Where is the African Swine Fever found?

ASF was first detected in East Africa in the 1920s, and then the virus was later spread to Europe in the late 1950s. The disease has been spreading globally for several years and since the first report of the virus in China in August 2018, there has been increasing concern over this disease in Asia and the Pacific.ASF continues to spread worldwide, threatening pig health and welfare.

The disease has reached multiple countries across Asia, the Caribbean, Europe, and the Pacific, affecting both domestic and wild pigs. And recently it is causing havoc in many Asian countries including India especially the North Eastern states.The disease was first detected in India at Assam in February 2020.

Apart from Assam the states of Mizoram, Meghalaya, Manipur, Nagaland, Sikkim, Tripura and Uttarakhand have also reported cases. However, the cases reported in North eastern Indian states can be potentially linked to international movement and trade.

What is the public health risk associated with this disease?

ASF is not a danger to human health as the virus cannot be transmitted from pigs to humans, but it has devastating effects on pig populations and the pig farmer’s economy. Neither direct contact with infected pigs nor eating pork originating from infected pigs can transmit the ASF virus to humans. In fact, only domestic pigs and wild boars (warthogs and bushpigs) are susceptible to the virus, in addition to soft ticks belonging to Ornithodoros genus that may act as biological reservoirs and vectors.

How the African Swine Fever spread?

The virus can be transmitted by direct or indirect contact between infected pigs. Transmission occurs via contact with faeces, bodily fluids or contaminated carcasses of infected pigs, as well as when pigs eat pork products that contain the ASF virus. It can also be indirectly transmitted through contaminated equipment, vehicles, footwear, feed, or clothing. This hardy virus can persist for approximately 5 months in boned meat stored at 40 C.

The virus can also be transmitted via Ornithodoros Soft ticks and biting flies which act as transmission vectors. And feeding of these vectors on neighbouring pig populations will transmit the disease to new hosts. ASF may also spread to populations of wild boar in the forests and wildlife sanctuaries. As an extremely contagious transboundary disease, it can swiftly cross national borders, spreading through live or dead bodies, even through packaged pork products.

Poor and marginal farmers afraid of having sick animals die on their hands dump them in the market, leading to distress-selling and more disease transmission. The dead pigs are also dumped in local rivers and ponds by the owners, leading to the rapid spread of contagions downstream of the river bed.

African Swine Fever and the COVID-19 pandemic

The COVID-19 pandemic is one of the most serious challenges faced by humanity. The disease has infected ~500 million people with SARS-CoV-2 and ~6 million have died so far. The disease also has disastrous effect on the mental, social and economic well-being of the affected person. On the other hand, ASF which is causing havoc in Asia and Europe since 2018-19 had similar devastating consequences on the pig population.

It is rather uncanny that these two pandemics originated at almost the same time and place. Due to the outbreak of ASF in Asia, there might be shortage of pork and disruption in meat trade which may lead to changes in the food habits of the people. And the meat from the other farm animals will not be enough to fulfil the overall demand.

As a result of which people might have to see the alternative meat source including the wild animals. This could bring a closer contact between the human and wild animal which may be harbouring different zoonotic diseases and result in spillover events, although at present there is no any scientific evidence to support this.

Nonetheless, we were unprepared for both pandemics, illustrating the importance of understanding the origins of pathogenic diseases and effective disease surveillance, management and mitigation.

Clinical signs of the disease:

The disease may occur in chronic, sub-acute or acute form depending upon the virulence of the strain causing the infection and the immune status of the infected pig. The incubation period for ASF is variable but is usually between 4-19 days. In the acute form of the disease caused by highly virulent strains, pigs usually die within 4-20 days post-infection with a high mortality rate of 95-100%.

Pigs develop a high temperature (40.50C), loss of appetite, vomiting, diarrhoea (sometimes bloody), reddening or darkening of the skin particularly around the ears and snout, gummed up eyes, laboured breathing, coughing, abortion, still births, weak litters, weakness and unwillingness to stand.The clinical signs of ASF are indistinguishable to those for Classical Swine Fever and also similar to other pig diseases such as Porcine Dermatitis and Neopathy Syndrome.

Diagnosis:

The prime focus for the control of ASF is still on early diagnosis due to absence of effective vaccines in controlling the disease.Laboratory confirmation is essential, and samples of blood, spleen, kidney, lymph nodes and tonsils in particular should be collected for virus isolation, detection of antigen, or PCR testing for viral DNA.

Methods for early diagnosis of the disease includes an immunoblotting assay, sandwich ELISA, Polymerase Chain Reaction (PCR), nested-PCR, TaqMan®PCR assay, hot-start multiplex PCR, real-time PCR, cross-priming amplification (CPA), polymerase crosslinking spiral reaction (PCLSR) and a loop-mediated isothermal amplification (LAMP) assay.

African Swine Fever Vaccines and Treatments:

Till date, there are no commercial vaccines or treatments available for the ASF. The pigs that survived the mild infection can shed the virus for at least 70 days. The only way to contain the virus in case of an outbreak is to either quarantine the pig population, if possible, or slaughter them. A vaccine against the ASF virus appears feasible, since pigs that recover from an infection are protected when challenged with a closely related strain.

Developing a universal vaccine has been challenging due to the limited cross-protection between different strains of the virus. Currently, 24 genotypes of ASF virus associated with distinct geographies in Africa have been identified based on the sequencing of the major capsid protein p72. Many laboratories around the world are working to develop a vaccine, with some promising results, but more work is required to ensure the safety and efficacy of these prototype vaccines before registration.

Prevention and control measures:

The most adequate preventive measure has to be by checking and stopping the spread of the virus. The demographic location of the vectors such as ticks and flies should be taken into account while mapping control measures.

o Maintain strict biosecurity measures: It is possible to prevent the spread of the virus by implementing strict biosecurity measures since without human assistance ASF virus cannot be transmitted over long distances.

o Do not allow the infected pigs and bedding material to leave the area of the farm premises where outbreak has been confirmed.

o Allow only essential visitors to enter your farm: Ensuring the farm workers and other essential visitors such as veterinarians are disinfected properly before entering the farm premises and should wear protective clothing and other PPE gears and wash their hands (or shower in if possible).

o Allow only vehicles and equipment into the farm if they have been cleaned and disinfected beforehand. Limiting the access for people and vehicles in and around the farm premises and in areas where pigs are reared can be of great help in containing the spread of the disease.

o Do not allow the people to enter the farm who may have been in contact with other pigs.

o Feeding of leftovers should be strictly avoided, no human food should be allowed into the pig facility and bio-security guidelines to be adhered strictly.

o No import of live animals, meat and meat products from regions where African swine fever occurs.
o Do not allow the staffs and visitors to bring pork products into the farm
o Do not allow catering waste / scraps to be fed to pigs - dispose of it safely.
o Prevent contact between the domestic and wild pigs.
o Disinfectant foot baths for visitors and working personnel should be installed.
o Early detection and humane killing of the pig population with proper disposal of carcasses with surveillance and detailed epidemiological investigation are deemed to be ensured.


For further details contact: -
Public Relations & Media Management Cell,
CAU, Imphal.
Email: prmmcell@gmail.com