How does African swine fever manifest

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African swine fever is a viral disease with a very high mortality rate that is harmless to humans. Synonyms - Montgomery's disease, African fever, South African swine fever, ASF. Pathology is very dangerous, spreads quickly and leads to large economic losses. Clinical symptoms are mild; laboratory diagnostics can confirm the final diagnosis. Sick animals today are not subject to treatment; preventive measures are taken to prevent them.

African swine fever

The etiology of the disease

What is African plague and what pathogen is it caused by? The cause of the pathology is a virus, the genetic material of which is contained in DNA, from the Asfaviride family, the Asfivirus genus. This virus has tremendous resistance to various adverse environmental influences:

• survives at a pH of 2 to 13 units (in both acidic and alkaline environments);
• in pickles and smoked meats, they remain active for weeks, or even months;
• survives for 7 years at a temperature of 5 ° C;
• at a temperature of 18-20 ° C - 18 months;
• at a temperature of 37 ° C - 30 days;
• during pasteurization at a temperature of 60 ° C, it survives for 10 minutes;
• lives in pork corpses from 17 days to 10 weeks;
• in feces - 160 days, in urine - up to 60 days;
• in the ground during the summer-autumn period it can be stored for up to 112 days, in winter and spring - up to 200 days.

Due to this high resistance of the virus, African swine fever and the causative agent of the disease can be transported over very long distances. It can be destroyed only by burning the corpses of pigs, using high doses of disinfectants (slaked lime, formaldehyde, etc.). In addition, the virus is extremely virulent, and even small doses can cause acute illness.

Epidemiology

The first cases of the disease were recorded at the beginning of the twentieth century in South Africa, from there it spread to Portugal, Spain, and other countries of southern Europe. In the 70-80s, the pathology was registered in South and North America, the USSR. Now the disease is a serious threat, because of it, pigs are almost not raised in Africa, their livestock is declining in Europe and America. In 2007, the outbreak was recorded in Georgia, in 2015 - in Ukraine, since 2008, the African plague, as reported by veterinary services, is regularly registered in the European part of Russia.

Sick pigs and virus carriers are the source of pathology. Even if the animal recovers, it continues to excrete the pathogen until the end of its life, therefore, all livestock are destroyed in the epizootic focus. The natural focus is African pigs, especially wild pigs. Their infection is latent and chronic, very rarely - in acute. Domestic pigs are more susceptible to the virus, especially European breeds. Even among wild boars in Europe, mortality is at the same level as among domesticated ones.

The African swine fever virus is transmitted by airborne droplets, alimentary. The main objects and things through which pigs become infected are water and food (especially feed that uses animal meat), care items, contaminated bedding. The virus can be transmitted through the clothing and shoes of people caring for sick pigs. Often, the virus enters the bloodstream through ticks, which are its natural reservoir. Flies and other blood-sucking insects can carry the infection. Often, the pathogen is mechanically carried by domestic birds and rodents.

Pathogenesis of the disease

The susceptibility of domestic pigs to the virus is very high, which is why the disease is so dangerous. The pathogen enters the body through mucous membranes and skin, even with microscopic damage, sometimes enters the bloodstream with insect bites. From the place of penetration, the virus enters the cells of the immune system (macrophages, neutrophils, monocytes), as well as the endothelial cells of blood vessels. Reproduction of the pathogen takes place in these structures.

After replication, the virus leaves the cells, destroying them. In the vessels and lymph nodes, foci of necrosis appear. The permeability of the vessels increases sharply, blood clots form in their lumen, and inflammation develops around the damaged structures. Anesthetized lymph nodes are found in various organs. Due to damage to the immune system, the ability of the pig's body to protect and resist other diseases is sharply reduced. Symptoms of the African plague are manifested, quickly leading to the death of the animal.

African plague clinic

The incubation period lasts 5-10 days. The disease of pigs, viral African plague, can occur in three forms: fulminant, acute and chronic. In the first case, it lasts 2-3 days and ends in death in 100%. The first symptoms and signs of African swine fever in such cases do not have time to develop. A farmer may find a herd that is completely healthy in the evening, dead in the morning.

In the second case, the clinical manifestations are more pronounced.

There are such signs of African swine fever:

• fever up to 40-42 ° C;
• cough, the pig begins to choke;
• vomiting interspersed with blood;
• the hind legs are paralyzed;
• constipation, less often bloody diarrhea;
• a clear, purulent or bloody fluid flows from the nasal passages and the eye;
• on the inner thighs, near the ears, on the abdomen, purple spots are visible, which do not brighten when pressed;
• bruising is visible on the conjunctiva, palate, tongue;
• purulent pustules and sores may appear in some places.

A sick pig tries to hide in the far corner of the shed, it lies on its side, does not rise to its feet, its tail unwinds. Pregnant sows lose their piglets when infected. For 1-3 days before death, the temperature in animals decreases.

African swine fever in a chronic and asymptomatic form is extremely rare and mild. Such variants are more typical for wild species in natural foci of the disease. The clinical picture is not pronounced, animals with this course of pathology gradually weaken, suffer from constipation, they have minor symptoms of bronchitis. Sometimes pinpoint hemorrhages or spots are found on the skin and mucous membranes. A chronic illness may end in recovery, but the virus remains in the blood, and pigs remain carriers of it forever. When signs of protracted pathology in pigs are found, laboratory diagnostics are mandatory.

Pathological changes and diagnostics

If ASF is suspected, a random examination of the corpses is mandatory. Pathological changes and histological signs of African plague are as follows:

• The skin on the abdomen, under the chest, behind the ears, on the inner thighs is red or dark purple.
• The mouth, nose, trachea are filled with pink foam.
• The lymph nodes are greatly enlarged, the pattern on the cut is marble, multiple hemorrhages are visible, sometimes the node resembles a continuous hematoma with black clots.
• The spleen is large, with multiple hemorrhages, areas of necrosis.
• The kidneys are also enlarged with hemorrhages in the parenchyma and on the walls of the dilated renal pelvis.
• The lungs are full of blood, a shade of gray with red, there are multiple bruises in the parenchyma, there are symptoms of pneumonia, fibrous cords are found between the alveoli (signs of fibrotic inflammation).
• The liver is full of blood, significantly enlarged, the color is gray with a clay tinge, uneven.
• The mucous membrane of the intestine and stomach swells, they reveal hemorrhages.
• In chronic pathology, bronchitis is found on both sides, an increase in lymph nodules in the lungs.
• In the asymptomatic form, only changes in the lymph nodes are visible: they have a marble pattern.

African swine fever has symptoms similar to common swine fever. To distinguish between 2 diseases, laboratory diagnostics are required. The method of PCR, fluorescent antibodies, hemadsorption is used. Also, biological tests are carried out, the material of sick animals is injected into pigs vaccinated against common plague. If they show pathology, the diagnosis is confirmed.

Treatment and prevention

A specific treatment, like a vaccine, has not yet been invented. It is not even allowed to try to treat mumps with symptomatic medications, as they will continue to shed pathogens. Prevention of African swine fever consists of measures in the outbreak and prevention of the introduction of viruses from other places.

Outbreak activities

If pigs show even the slightest signs of possible ASF, the entire herd must be destroyed. Preliminary laboratory diagnostics are carried out to confirm the diagnosis. Especially in cases where the clinical picture is not completely clear. Measures carried out in the focus of confirmed infection consist of the following points:

• Yards and farms in which African swine fever has been detected are subject to strict quarantine.
• All animals are killed by any bloodless method.
• All carcasses are burned, and they cannot be taken out of the quarantined place.
• It is advisable to burn the corpses together with the pigsty and utility rooms.
• Equipment, leftovers of feed, bedding, clothes of people caring for pigs are also subject to destruction.
• Ash is mixed with slaked lime and buried to a depth of at least one meter.
• Premises that cannot be burned are thoroughly disinfected. Use caustic soda 3% or formaldehyde 2%.
• The same activities are carried out on all pig farms that are located within a radius of 25 km from the infected area, even completely healthy pigs are killed.
• Across the entire territory, the destruction of ticks and other blood-sucking insects, rodents, and stray animals is carried out.
• While the quarantine lasts (an average of 40 days), it is prohibited to export and sell any products obtained from animals (not necessarily pig meat) outside the zone.
• For 6 months after the outbreak occurred, it is prohibited to export and sell any plant-based agricultural products.
• Pigs should not be bred throughout the year throughout the quarantine area, all this time there is a risk of a second outbreak.

Veterinary services must ensure that the events are carried out; for this, there are certain articles of the law in Russia and other countries. Such strict rules and control measures allow at least partially to stop the spread of the disease to other regions. Unfortunately, they cause enormous economic damage to farms. In many countries, a system of material compensation has been developed, but it does not cover all losses. How events are carried out in the focus of infection, you can watch the video.

How to prevent the virus from entering farms

We have already found out that if signs of African plague appear, the entire herd will have to be destroyed. Is it possible to prevent this disease in your household, what control measures are needed? In the world today, precise recommendations have been developed for the prevention of this dangerous disease. Here is a list of them:

• It is necessary to exclude the presence of strangers in the pigsties.
• Pigs are best kept free from walking.
• Deratization and disinfestation are regularly carried out in the premises.
• The animals are fed exclusively with industrial feed, which are processed not lower than at 80 ° C.
• The farms protect against the penetration of wild birds and animals, stray dogs and cats.
• You cannot use inventory in the barn that has not undergone special processing.
• All transport that enters the farm must be carefully handled.
• Pigs are slaughtered at special points where animals and carcasses are examined by veterinarians.
• You can buy animals only if they have all the veterinary certificates.
• Before buying, you need to find out if there is ASF in the area.
• Animals are vaccinated against all other diseases.
• If the animal has certain symptoms, be sure to inform the veterinary service.

Some people ask if African swine fever is dangerous to humans or not? For people, the disease is not dangerous. But along with food, it can be passed on to other pigs in the region. Especially in cases where animals are fed with food waste. Therefore, it is strictly forbidden to export any products from disadvantaged territories, even if no one is going to sell them.