African Swine Fever (ASF) A Newly Emerged fatal Disease of Pigs in India: Dos and Don’t dos
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.
African Swine Fever: Dos and Don’t dos
African Swine Fever (ASF) is ‘a highly infectious and contagious hemorrhagic viral disease of pigs, wild boar/feral pigs’. It is a very lethal disease with mortality rates of 95-100%. ASF has been identified in India for the first time in domestic pigs in the year 2020 from Arunachal Pradesh and Assam and now it has spread to almost entire northeastern states. In absence of vaccine, on-farm and community level biosecurity measures are extremely important to further spread the disease. The ASF is different from Classical Swine Fever (CSF) for which vaccine is also available. However, clinical symptoms of both are similar and it is difficult to differentiate just by looking on clinical symptoms. ASF virus does not infect human (non-zoonotic) or other livestock species. Hence, it is not a public health risk.
Nature of the virus and Epidemiology, survival in environment: It is caused by the Asfivirus of the Asfarviridae family, a very stable DNA virus. All members of the suidae family like pigs (domestic and wild) and warthogs are susceptible. The disease cycle and pattern of virus transmission is very complex and the disease could be transmitted through anything (live pig/inanimate objects/pork or pork products/vehicle/feed/water/human/birds etc.) which comes in contact with an ASF virus. The disease may manifest within 3 days of infection and go on till the 13th-14thday in acute cases while chronic cases can develop over 2-15 months. The ASF virus is stable over a wide range of physical and chemical challenges. The virus survives readily through a wide range of pH (3.9 – 11.5). The virus can survive up to 10 days to 140 days in different environment. Normal disinfectants like phenyl, potassium permanganate, dettol, other household disinfectants etc may not be too effective.
Mode of transmission – Direct contact with sick pigs, contaminated carcasses, urine, dung, hair, saliva, blood, contaminated feed, contaminated footwear and clothing, contaminated soil, contaminated water and animals or birds which could have contacted any contaminated material, birds or ticks.
Common symptoms in pigs:
- Per-Acute form –High fever (41-42 °C) and sudden death within 1-3 days. There could be vomiting.
- Acute form – High fever (40-42°C)with reddening of skin of ear tip, tail, ventral aspects of chest and abdomen, and death within 6-9 days for highly virulent strains, or 11-15 days for moderately virulent isolates. Mortality upto 90-100%
- Sub-acute form –Slight fever, reddening of skin and death within 15-45 days. Mortality between 30-70%
- Chronic form –The lethality rate in this form is less than 30%. Pig shows irregular peaks of temperature, respiratory signs, necrosis in skin, ulcer, arthritis, joint swelling.
Biosecurity measures
1. Do not purchase pigs or piglets from market or unknown sources.
2. Smuggling of pigs/pork in any form must be strictly stopped.
3. Quarantine of newly purchased pigs (either for slaughtering or rearing) for 21 days.
4. All pig/pork/feed carrying vehicles must be sprayed with disinfectant solution at all entry point.
5. Sick animals should never be transported.
6. A perimeter of at least 6 feet must be kept free of bushes/trees/vegetation around the pig shed and it must be fenced in.
7. Hunting of wild boar should be prohibited.
8. Carcass should be buried at least 6 feet deep. The carcass should be sprinkled heavily with raw lime or bleaching powder and then the pit may be filled up with earth. After filling up, the earth mound must be sprinkled heavily with bleaching powder or sprayed with sodium hypochloride solution.
9. The pen in which the pig had got sick and died must be thoroughly disinfected and all the areas where the carcass was dragged along must be disinfected.
10. Animal Husbandry department should be informed in case of suspected outbreaks of ASF.
Important Points to remember:
- Do not visit an area where ASF outbreak is reported.
• Do not let anyone enter your farm/ visit your pig-sty.
• Never enter your farm area or pig-sty after returning from market or out of town trips.
• Always wash hands/bath and change clothes and footwear before entering the pig keeping area. Preferably, keep a separate set of clothes and footwear for the pig area.
• Always disinfect footwear and hands/gloves with suitable disinfectant.
• Do not let dogs/cats/chicken /pigeons or any birds enter your pig keeping area.
• Always boil kitchen waste before feeding; the boiling temperature must be maintained for at least 15-20 minutes.
• If a pig is sick/not eating /depressed, it should be attended to at the end of the work session only after attending to the healthy animals. Never re-enter the healthy animal pens after attending a sick animal.
Farm disinfection protocol: Bleaching powder, Sodium hypochlorite, Caustic soda (sodium hydroxide), Potassium peroxymonosulfate and glutaraldehydes. These are available under various trade names like viroxide, hypoclean, sokrena, B2 etc.
Sodium hypochlorite 5-12 % in water could be used otherwise the bleaching powder solution may be prepared as discussed below.
1. Mix bleaching powder in water at a rate of 1 teaspoon bleaching powder per litre of water and mix such that the bleach is properly dissolved.
2. Let it settle for two hours
3. Take supernatant in a sprayer and use for spraying over the pig sty.
4. Before using the solution for spraying, the pen should be cleared of debris and washed with water.
General Sanitary protocol for farm
1.Farm buildings should have a fenced perimeter leaving a gap of at least 30-50 feet between wall/fence and the buildings. Farm complex should have only one main entrance and an alternative which must be kept locked unless needed.
2. Entry in the farm should be strictly banned and farm workers should only enter the farm after disinfecting their clothes, footwear etc.
3. Daily disinfection of farm buildings and equipment in the morning and evening.
4. All vehicles and articles entering the farm must be sanitised.
5. Farm worker must never handle raw meat from the market or ever enter a sick animal’s pen in the neighbourhood.
6. The animal attendant must avoid going to purchase meat from the wet market.
7. They must not attend to sick pigs other than those in the farm.
8. Farm clothes must be soaked in disinfectant, washed and ironed.
By- R Talimoa Mollier and Mahak Singh
ICAR Research Complex for NEH Region, Nagaland Centre, Medziphema
Source-www.thesangaiexpress.com/Encyc/2022/8/27/Dr-Mangsatabam-Norjit-SinghAfrican-Swine-Fever-ASF-is-a-highly-contagious-devastating-and-deadl.html
PHOTO CREDIT-WOAH
