How does African swine fever manifest
African swine fever is a viral disease with a very high mortality rate, harmless to humans. Synonyms - Montgomery disease, African fever, South African swine fever, ASF. Pathology is very dangerous, spreads rapidly and leads to large economic losses. Clinical symptoms are mild, laboratory diagnosis can confirm the final diagnosis. Sick animals are not subject to treatment today; preventive measures are taken to prevent it.
African swine fever
Etiology of the disease
What is the African plague and what pathogen is it caused. The cause of the pathology is a virus, the genetic material of which is contained in DNA, from the Asfaviride family, the genus Asphivirus. This virus has amazing resistance to various adverse environmental influences:
- survives at pH from 2 to 13 units (both in acidic and alkaline environments);
- in pickles and smoked meats, weeks and even months remain active;
- at a temperature of 5 ° C survives for 7 years;
- 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, 10 minutes survive;
- lives in pig 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 up to 112 days, in winter and spring - up to 200 days.
Due to the high resistance of the virus, African swine fever and the causative agent can be transported over very long distances. It can only be destroyed by burning the corpses of pigs using high doses of disinfectants (hydrated lime, formaldehyde, etc.). In addition, the virus is extremely virulent, even small doses can cause an acute illness.
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 70-80 years, pathology was recorded 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 number is declining in Europe and America. In 2007, an outbreak was recorded in Georgia, in 2015 - in Ukraine, since 2008, African plague, according to veterinary services, is regularly recorded in the European part of Russia.
The source of the pathology is sick pigs and virus carriers. Even if the animal recovers, it continues to secrete the pathogen until the end of life, therefore, in the focus of epizootics, the entire population is destroyed. The natural focus is African species of pigs, especially wild ones. In them, the infection proceeds in a latent and chronic form, 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 virus of African swine fever is transmitted by airborne, alimentary route. The main objects and things through which pigs are infected are water and food (especially feeds that use animal meat), care items, and infected litter. The virus can be carried with the clothes and shoes of people caring for sick pigs. Often the virus enters the bloodstream through ticks, which are its natural reservoir. Flies and other insects that suck blood can carry the infection. Often mechanically by the pathogen, domesticated birds and rodents are carried.
Pathogenesis of the disease
The susceptibility of domestic pigs to the virus is very high, because the disease is so dangerous. The pathogen enters the body through the mucous membranes and the skin, even with microscopic injuries, sometimes penetrates the blood when insect bites. From the point of entry, the virus enters the cells of the immune system (macrophages, neutrophils, monocytes), as well as into the endothelial cells of blood vessels. In these structures, the pathogen propagates.
After replication, the virus exits the cells, destroying them. In the vessels and lymph nodes, foci of necrosis occur. Vascular permeability increases sharply, blood clots form in their lumen, inflammation develops around damaged structures. In various organs, anesthetized lymph nodes are found. Due to damage to the immune system, the pig’s ability to protect and resist other diseases is sharply reduced. The manifestations of the symptoms of African plague, 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 in 100% ends in death. The first symptoms and signs of African plague in pigs in such cases do not have time to develop. A farmer who is quite healthy in the evening can find the herd dead in the morning.
In the second case, clinical manifestations are more pronounced.
The following signs of African swine fever are distinguished:
- fever up to 40-42 ° C;
- cough, pig begins to choke;
- vomiting with disseminated blood;
- hind legs paralyzes;
- constipation, less commonly bloody diarrhea;
- a clear, purulent or bloody liquid flows from the nasal passages and eyes;
- on the hips from the inside, near the ears, on the stomach, purple spots are visible that do not lighten when pressed;
- bruising is visible on the conjunctiva, palate, tongue;
- purulent pustules and sores may appear in some places.
The sick pig tries to hide in the far corner of the barn, it lies on its side, does not rise to its feet, its tail spins up. Pregnant sows lose piglets when infected. 1-3 days before death, the temperature in animals decreases.
African swine fever in chronic and asymptomatic forms is extremely rare and mild. Such variants are more typical for wild species in the natural foci of the disease. The clinical picture is not expressed, animals with this course of pathology gradually weaken, suffer from constipation, they have minor symptoms of bronchitis. Sometimes, spot hemorrhages or spots are found on the skin and mucous membranes. A chronic disease may end in recovery, but the virus persists in the blood, pigs remain carriers of it forever. When signs of a protracted pathology are found in pigs, laboratory diagnosis is mandatory.
Pathological changes and diagnosis
If ASF is suspected, a selective inspection of the corpses is mandatory. Pathological changes and signs of histological African plague are as follows:
- The skin on the abdomen, under the chest, behind the ears, on the inner sides of the thighs is red or dark purple.
- Mouth, nose, trachea are filled with pink foam.
- Lymph nodes are greatly enlarged, the picture on the section is marble, multiple hemorrhages are visible, sometimes the node resembles a solid 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 enlarged 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 (signs of fibrous inflammation) are found between the alveoli.
- The liver is full of blood, significantly enlarged, the color is gray with a clay shade, uneven.
- The mucous membrane of the intestines and stomach swells, hemorrhages are revealed on them.
- In chronic pathology, bronchitis is found on both sides, an increase in lymph nodes in the lungs.
- With an asymptomatic form, only changes in the lymph nodes are visible: they have a marble pattern.
African swine fever has symptoms similar to the usual plague of this animal species. In order to distinguish between 2 diseases, laboratory diagnosis is mandatory. The method of PCR, fluorescent antibodies, hemadsorption is used. Biological tests are also carried out, the material of sick animals is administered to pigs vaccinated against ordinary plague. If they show a pathology, the diagnosis is confirmed.
Treatment and prevention
Specific treatment, like a vaccine, has not been invented today. It is not allowed to even try to treat pigs with symptomatic drugs, as they will continue to excrete pathogens. Prevention of African swine fever consists of measures in the outbreak and prevention of virus entry from other places.
If at least the slightest signs of possible ASF are found in the pigs, the whole 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 taken at the site of confirmed infection consist of the following items:
- Strict quarantine is imposed on yards and farms in which African swine fever is detected.
- All animals are killed by any bloodless method.
- All carcasses are burned; however, they cannot be taken out of the place where quarantine is imposed.
- It is advisable to burn corpses together with a pigsty and utility rooms.
- Destruction is also subject to inventory, residues of feed, bedding, clothes of people caring for pigs.
- Ash is mixed with slaked lime and buried to a depth of not less than a meter.
- Rooms that cannot be burnt are thoroughly disinfected. Use caustic soda 3% or formaldehyde 2%.
- The same measures are carried out at all pig farms, which are located within a radius of 25 km from the infected area, kill even completely healthy pigs.
- Throughout the territory they carry out the destruction of ticks and other blood-sucking insects, rodents, stray animals.
- While quarantine lasts (on average 40 days), no products obtained from animals (not necessarily pig meat) can be exported and sold outside the zone.
- For 6 months after the moment of the outbreak, it is forbidden to export and sell any plant agricultural products.
- Pigs cannot be bred throughout the year throughout the quarantine, all this time there is a danger of a second outbreak.
Veterinary services must ensure that events are held, for this there are certain articles of the law in Russia and other countries. Such strict rules and control measures allow at least partially stop the spread of the disease to other regions. Unfortunately, they cause huge economic harm to households. Many countries have developed a material compensation system, but it does not cover all losses. How events are held in the focus of infection, you can watch the video.
How to prevent virus from entering farms
We have already found out that when signs of the African plague appear, the whole 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 without walking.
- On the premises, deratization and pest control are regularly carried out.
- Animals are fed exclusively with industrial feeds that undergo processing no lower than at 80 ° C.
- Farms protect from the penetration of wild birds and animals, stray dogs and cats.
- Inventory that has not undergone special processing should not be used in a stable.
- All vehicles that enter the farm must be carefully handled.
- Slaughter of pigs is carried out at special points where veterinarians examine animals and carcasses.
- You can buy animals only in cases where they have all the veterinary certificates.
- Before buying, you need to find out if there are any ASF in the area.
- All other animal diseases are vaccinated.
- If the animal has any symptoms, be sure to inform the veterinary service.
Some ask whether African swine fever is dangerous to humans or not. For people, the disease is not dangerous. But along with the products, it can be transmitted to other pigs in the region. Especially in cases where animals are fed with waste from the food industry. Therefore, it is strictly forbidden to export any products from dysfunctional territories, even if no one is going to sell them