Classical swine fever and its consequences
Classical swine fever is a viral infectious pathology that most often occurs in an acute form, less often in a subacute and chronic form. With this pathology, lymph nodes, bone marrow, hematopoietic organs, and intestines are affected. The disease is manifested by fever, hemorrhagic rash, diarrhea and constipation. The mortality rate of the livestock reaches 80-100%, the treatment has not yet been developed, emergency sanitary measures are being carried out in the lesion focus. All pigs are vaccinated to prevent disease. Plague is not transmitted to humans and is not dangerous to other animals.
Classical swine fever
Etiology
Classical swine fever is caused by Pestivirus from the Flaviviride family. Its genetic material is contained in RNA. From above, the virion is covered with a protein-lipid membrane. The size of the particles is 40-60 nm. The virus is very stable in the external environment, it tolerates drying, low temperatures and freezing well. The optimum pH for it is 5-10 units. When pasteurized, it dies no earlier than an hour later. Here are some indicators of its sustainability:
- stored in chilled meat and carcasses for 2-4 months;
- in frozen meat - several years;
- in pickles - about a year;
- in smoked meats - 1-1.5 months;
- at a temperature of 2-4 ° C, it lasts 4-6 months;
- at a temperature of 37 ° C it remains active up to 18-20 days;
- at a temperature of 70-80 ° C, disinfection occurs only after an hour;
- when boiled, it dies instantly.
The classical swine fever virus is sensitive to ethers, chloroform, trypsin. The best disinfecting solutions for its neutralization are 2% sodium hydroxide, 20% bleach, 3-6% oil solution of cresol.
There are 3 serotypes of the pathogen: A, B and C. Serotype A causes the classic picture of acute swine fever, as well as its fulminant forms. Serotype B of the plague pathogen causes infection in piglets, atypical and chronic variants of the course in adult animals. Frequent epizootic spread, as in serotype A, is not observed. Serotype C virus is used in laboratories to obtain material for vaccines.
Epidemiology and pathogenesis
Classical swine fever was first described in 1810 in Tennessee. After 20 years, outbreaks have been reported in Ohio. Because of this, the disease was initially called "American Swine Fever". In the middle of the 19th century, pathology began to spread in Europe, and by the end of the century it had spread to South Africa and the south of the American continent.
The only source of classical swine fever is sick pigs and infected virus carriers. The virus is also preserved in the natural environment, in the wild boar population. Neither man nor other animals are afraid of the disease, they can only be mechanical carriers.
The virus is excreted in urine, feces, nasal secretions, saliva, vomit, and abortive material in sows.Once in the external environment, the pathogen persists for a long time and can be transported over long distances.
The main transmission factors are contaminated feed, especially animal products such as meat and bone meal. Also, the virus can be carried along with bedding, inventory, often infections occur when transporting livestock in transport, where sick pigs or virus carriers used to stay. Rats, other rodents, strangers on the pig farm can become carriers.
Infection passes through alimentary or airborne droplets. Having penetrated the bloodstream through the mucous membranes, the classic swine plague virus spreads throughout the body. It is tropic to almost all organs, cells and tissues, but its highest concentrations are found in the lymph nodes, the walls of blood vessels and intestines, and in the bone marrow.
In the bloodstream, the pathogen is detected within 6-7 hours after infection. It begins to multiply intensively in lymphocytes, then it is brought into the lymph nodes, where it can be detected 16 hours after the first contact. During the first 3 days, the pathogen enters the lungs and intestines, approximately on the 4th day - into the heart, uterus and other organs. The active release of viral particles begins 6 days after infection. Very often this happens even before clinical signs appear.
The clinical picture of the disease
The incubation period for swine fever is 3-9 days. In rare cases, it can drag on for 12-20 days. Pathology proceeds in fulminant, acute, subacute and chronic variants. The first 2 forms are most typical for epizootics, a subacute and prolonged course is possible in sporadic cases provoked by the serotype B virus.
Lightning shape
Swine fever symptoms develop rapidly, within 1–2 days. Animals become lethargic, their temperature rises to 40-42 ° C, vomiting appears, and appetite is completely absent. Breathing and heartbeat become more frequent, a hemorrhagic rash and extensive red spots appear on the skin. How they look is best seen in the photo. Most often, the fulminant or hyperacute form of swine plague is observed in young individuals.
Acute form
The duration of this form of the disease is 3-7 days. Pigs also have fever, vomiting and constipation. They lie buried in the litter most of the time, do not eat. In the future, constipation is replaced by diarrhea, blood streaks are visible in the feces. The amount of urine is reduced, it often becomes dark brown. Females abort, mucus, pus flow from the nose and eyes, sometimes the discharge becomes bloody.
In some areas of the body, pustules appear on the skin, from which yellow-green pus is released. A bright hemorrhagic rash is visible, when draining, extensive red spots are formed that do not disappear when pressed. The stigma, ears and legs are bluish, weakness progresses. The number of lymphocytes in the blood decreases.
There is a nervous form of classic swine fever. With this type of illness, the temperature can remain normal. In animals, convulsions or nervous twitching of the muscles appear. The hind legs are weakened, and paresis or paralysis may occur. Periods of arousal in a pig are replaced by apathy and drowsiness. The animal dies after 1-2 days.
Subacute form
Subacute classical swine fever and the symptoms of such a pathology develop with a long course of the acute form with a not very pronounced clinic. The temperature in animals is not very high. Signs of dehydration, diarrhea, and cough come to the fore. Animals are lethargic, lose weight sharply, extensive purple or red spots, traces of hemorrhages are visible on the skin. Pus is discharged from the nose and eyes. Recovery is extremely rare.
Chronic form
Chronic swine fever is rare.Sometimes this course is observed in vaccinated animals with insufficient levels of antibodies after vaccination. The disease lasts 1-2 months. Body temperature may remain normal or slightly rise. Animals gradually lose weight, the backside sharpens and sags, the back sags. The pig has no appetite, most of the day it lies buried in the litter.
The lesions of the gastrointestinal tract and the respiratory system come to the fore. Purulent-fibrous inflammation develops in the stomach, intestines or lungs. Pigs vilify, sometimes there is blood in the feces, the smell is offensive. On the part of the respiratory system, pneumonia, pleurisy is diagnosed, the pig wheezes, coughs. Breathing is heavy, rapid. Purulent conjunctivitis and serous-purulent rhinitis are characteristic of this form. Sometimes the chronic form goes away with periods of remission and exacerbation. In some cases, the symptoms are not pronounced. The latent and asymptomatic form is the most dangerous, since a sick animal becomes a source of infection.
Complicated forms
Swine fever can be complicated by salmonellosis or pasteurellosis. In the first case, the intestinal form of the disease develops. Abundant fetid diarrhea appears, feces of gray-green color, watery, with mucus, blood. Salmonellosis is transmitted from sick animals to humans, therefore, with such a complication, you should be especially careful. With pasteurellosis, pulmonary symptoms occur: cough, shortness of breath, wheezing, signs of bronchitis and pneumonia.
Pathological picture and diagnosis
When an outbreak of classical swine fever is registered on a pig farm, additional laboratory diagnostics are required. First, an autopsy is performed on the dead pigs. Pathological changes in this disease are quite striking:
- the skin on the belly, the inner side of the thighs, the chest is of a purple hue with multiple hemorrhages;
- the lymph nodules on the cut have a marble pattern, are enlarged, their color is purple or completely black;
- in the lungs, hemorrhages, heart attacks, multiple spots on the surface are detected;
- heart with multiple hemorrhages along the vessels, in the epicardium and pericardium;
- the spleen is not greatly enlarged, wedge-shaped infarctions are revealed along the periphery, facing the wider part of the organ, this is a typical symptom of CSF;
- kidneys of sick individuals with signs of circulatory insufficiency, anemic, with punctate hemorrhages on the mucous membrane of the calyces;
- the stomach and intestines are inflamed, bruises are visible under the mucous membrane (especially pronounced on the 7-9th day of illness);
- with a subacute course, enteritis and gastritis with hemorrhages and bleeding are observed;
- with chronic plague in the stomach and intestines, ulcers with areas of necrosis, severely swollen lymph nodes in the mesentery, with ulcerations are revealed. These symptoms are especially pronounced in the cecum and colon.
Confirm the diagnosis of classical swine fever by examining blood, lymph nodes, bone marrow and spleen in the laboratory. Virological studies are performed by PCR, enzyme-linked immunosorbent assay, and fluorescent antibodies. Use biological samples by injecting the material into non-immunized piglets. It is possible to differentiate pathology from such diseases:
- African swine fever, or ASF;
- salmonellosis;
- streptococcal skin infection, or erysipelas;
- Aujeszky's disease;
- dysentery;
- gastroenteritis;
- pasteurellosis;
- flu and parainfluenza.
When making a diagnosis, it should be borne in mind that this type of pathology is especially dangerous. It is necessary to take control measures that are prescribed by law.
Treatment and prevention
The treatment of classical swine plague has not been developed, therefore all sick animals must be destroyed. Although the pathology is not transmitted to humans, it is impossible to eat meat: the pathogen remains in it for a long time, it can be imported to other territories, causing epizootics among animals.All carcasses must be burned after slaughter. All farms in the region are quarantined, an emergency is declared, and it is prohibited to export meat products outside of it.
The most reliable way to prevent classic swine fever is by vaccination. Vaccinations are given to piglets with live inactivated vaccines in the first weeks of life. The effect of vaccinations is maintained throughout the year. The vaccine is administered in the form of injections. There are also oral medications that are given to young animals in farms or regions suspected of having infection. In the event of an outbreak of epizootics in pigsties, aerosols are sprayed into weakened vaccine viruses.
Control measures for any infection will not be effective if it is not prevented in time. To prevent the spread of viruses of classical plague on farms, disease and death of livestock, the following measures should be taken:
- Buy only vaccinated animals with all veterinary certificates from safe farms and regions.
- Newly arrived pigs must undergo quarantine for a month and be kept separate from the rest of the herd.
- Inventory, transport, household items, clothing belonging to a person should be periodically disinfected.
- The pigsty and walking areas must be properly fenced to prevent stray cats and dogs, wild animals, and rodents from entering.
- Food and water must be disinfected, it is better to buy industrial feed that is heat treated.
- In the pigsty, deratization should be carried out from time to time, since rodents are mechanical carriers of infection.
If classic swine fever breaks out on the farm, quarantine is imposed for 40 days, the herd is subject to liquidation. Time is counted from the death of the last animal. After that, a thorough disinfection of the premises is carried out. Litter and cheap inventory are burned. Slaked lime, bleach, and cresol are used for disinfection. Dilute the funds as the instruction ascribes.