Characteristics of the pathogen and specific features of the epizootiology of anthrax in livestock animals

Anthrax is a deadly infectious disease that affects all types of livestock, wild animals, and humans. The disease follows an exclusively acute course, accompanied by sepsis, intoxication, and the formation of carbuncles. For any farm, an outbreak of this disease means strict quarantine and serious economic losses.

The disease has been known since ancient times. The first references to it date back to approximately 600 BC, and in the works of Hippocrates, Galen, and Celsus, it is described as "sacred" or "Persian fire." In European countries, major epizootics were recorded in 826, 992, and 1682. In Russian chronicles, the disease is mentioned under the years 978, 1158, and 1284, and massive devastating outbreaks were recorded in the 14th and 18th centuries, particularly affecting Siberia and the European part of the country.

The causative agent of anthrax and its resistance

The causative agent of the disease is a Gram-positive, spore-forming, aerobic bacillus. In the animal's body, it forms a capsule that protects it from the immune system (the vaccine strain does not form a capsule). Upon exposure to oxygen, the bacterium transforms into a spore form. In a closed, unopened carcass, spores are not formed because oxygen is absent there.

The resistance of the bacterium depends on its form. Vegetative forms quickly perish under the influence of environmental factors and disinfectants. Spores, however, are capable of maintaining viability in water for years and in the soil for decades. The preservation of spores is also facilitated by the salting of meat and the drying of hides.

Form of the pathogen	Exposure factor	Time until bacteria death
Vegetative form	Decomposition in an unopened carcass	7 days (microbes undergo lysis)
	Heating to 60 °C	15 minutes
	Boiling	Instantly
	Direct sunlight	Several hours
Spore form (spores)	Dry heat at 120–140 °C	2–3 hours
	Autoclaving at 120 °C	5–10 minutes
	Boiling	15–30 minutes
	10% sodium hydroxide solution	2 hours
	1% formaldehyde solution	2 hours

Epizootiology, symptoms, and measures for suspected infection

Most susceptible to the infection are large and small ruminants, buffaloes, horses, donkeys, deer, and camels. Pigs show lower susceptibility, and it is only possible to infect poultry under experimental conditions. The main source of infection is sick animals, which shed the pathogen with bloody fluid during their agony.

The infection is considered soil-borne and is characterized by stationary status: spores lie in the soil on pastures for decades. Animals become infected via the alimentary route while eating grass or contaminated feed. The peak incidence occurs during the summer grazing period, although isolated outbreaks are possible in winter as well.

• Incubation period — from several hours to 6–8 days (average 2–3 days)
• Death in the peracute course — from several minutes to 1–2 hours
• Death in the acute course — after 2–8 days
• Death of vegetative forms in a closed carcass — after 7 days

The disease occurs in septic, carbuncular, abortive, intestinal, pulmonary, or anginal (in pigs) forms. The peracute course manifests as fever, rumen tympany, discharge of bloody foam from the nose and mouth, tarry blood from the anus, and blood in the urine. In the acute course, symptoms develop more slowly; colic often occurs in horses, and with the carbuncular form, dense edema forms on the body.

If the carcass was opened by mistake, the signs of anthrax will include non-clotting dark blood, a dark-red color of the skin underside, and multiple hemorrhages in the tissues. The spleen is then sharply enlarged, and a scraping from its cross-section appears as an abundant, tar-like mass. If the disease is suspected, a veterinarian must collect samples for the laboratory.

1. Take thick blood smears from the ear veins of a fresh carcass or cut off the entire ear of the animal.
2. The site of the skin incision on the carcass must be cauterized to prevent the leakage of contaminated blood.
3. Send the material to the laboratory for microscopic examination.

All suspicious animals are immediately isolated in a separate room. For emergency treatment, veterinarians use hyperimmune anti-anthrax serum. Its therapeutic effect is enhanced by the intramuscular administration of antibiotics:

• penicillin or bicillin;
• streptomycin;
• tetracycline;
• enrofloxacin.

Prevention of anthrax and quarantine measures

Timely vaccination and monitoring of potential hotspots are the only reliable ways to protect the herd from anthrax. Natural infection leaves animals with lasting immunity; however, in practical animal husbandry, the emphasis is on planned preventive vaccination. To create active artificial immunity, a live vaccine from the 55 VNIIVViM strain is used.

• Immunity development period — 10 days
• Protection duration — up to 12 months
• Vaccination frequency — 1 time per year

Preventive vaccination is performed annually in stationary-unfavorable areas where disease outbreaks have been previously recorded. All susceptible livestock animals must be vaccinated: adult cattle, sheep, goats, and horses. Swine are not vaccinated against anthrax.

If a disease is detected on a farm, a strict quarantine is immediately imposed. To localize the outbreak and protect healthy livestock, the veterinary service must execute a strictly defined set of actions.

1. Isolate sick and suspected animals for subsequent treatment.
2. Carry out emergency immunization for all remaining susceptible livestock.
3. Change the pasture and disinfect the vacated facilities.
4. Burn infected manure and carcasses of dead animals.
5. Carry out thorough disinfection of livestock housing areas and soil sanitation.

For routine disinfection of facilities, a 20% solution of chloride of lime or a 10% solution of sodium hydroxide is used. The treatment is carried out three times at 1-hour intervals. Areas where sick animals were kept or carcasses were located are disinfected with a 10% hot caustic soda solution, a 4% formaldehyde solution, or chlorine-containing preparations, and chloride of lime is used for soil sanitation.

The quarantine is lifted from the farm 15 days after the last case of death or recovery of an animal. Before lifting restrictions, it is mandatory to verify that vaccinated animals have no complications or pathological reactions to the vaccinations.

Foot-and-mouth disease: transmission routes, virus survival, and symptoms

Foot-and-mouth disease is an acute viral disease of cloven-hoofed animals that spreads instantly through a herd. The disease is accompanied by high fever, formation of aphthae on the oral mucosa, udder skin, and in the hoof area. The causative agent is an RNA-containing virus, which is divided into 7 serological types: O, A, C, SAT-1, SAT-2, SAT-3, and Asia-1. Recovering from one virus type does not protect the animal from infection by the other six.

The foot-and-mouth disease virus is characterized by high survival in the environment and in animal products. On mountain pastures, it maintains activity until the next grazing season, and in salted and smoked products, it lives for up to 50 days. In milk, the virus is inactivated at a temperature of 65 °C in 30 minutes, at 70 °C in 15 minutes, and dies in a few seconds at 80–100 °C. In fresh meat, the pathogen is destroyed naturally due to the accumulation of lactic acid during maturation.

Environment or environmental conditions	Virus survival period
Wastewater during cold period	103 days
Wastewater in autumn	49 days
Wastewater in summer	21 days
Animal hair coat	50 days
Personnel clothing	100 days
Livestock facilities	70 days

For facility disinfection, a 2% formaldehyde solution and a 1–2% caustic soda solution are best. These agents are guaranteed to destroy the foot-and-mouth disease virus after 10–30 minutes of exposure.

Most susceptible to the infection are cattle">cattle and swine, whereas sheep, goats, and wild ungulates are affected less frequently. Sources of the virus are sick animals and latent virus carriers, which excrete it into the environment through saliva, milk, urine, and feces for over 400 days. Infection occurs via contaminated feed, water, equipment, by licking objects, through micro-traumas of the udder skin, or by the aerogenic route when kept together.

The incubation period lasts from 36 hours to 7 days, after which the animal's body temperature rises sharply to 41 °C and higher. Affected individuals experience a drop in milk yield, cessation of rumination, increased pulse, edema of the coronary band, and profuse salivation from the mouth with characteristic smacking sounds. After 3 days, the temperature drops and exanthema appears — lymph-filled blisters (aphthae), which burst after 1–3 days, leaving ragged, painful erosions. Without timely veterinary assistance, necroses and abscesses develop in the oral cavity, and panaritiums and phlegmons develop on the legs.

Measures during a foot-and-mouth disease outbreak: diagnosis, treatment, and quarantine

For effective containment of a foot-and-mouth disease outbreak, the diagnosis is made based on the analysis of epizootiological data, clinical signs, and laboratory research results. The course of the disease has its peculiarities: young cattle die from myocarditis within 12–30 hours against a background of high fever and weakness; in swine, the limbs, snout, and udder are affected (animals move by crawling on their carpal joints), while in sheep, symptoms are less pronounced. During necropsy, aphthae are found on the mucous membranes of the oral cavity, rumen, and omasum, on the skin of the udder and limbs, and gray-yellow or whitish spots ("tiger heart") and accumulation of transudate in the pericardium are detected in the myocardium.

Once the diagnosis is confirmed, sick livestock animals must be immediately isolated. They should receive symptomatic treatment aimed at supporting cardiac activity and healing mucous membranes. Therapy is performed according to the following scheme:

1. Provide isolated animals with soft, nutritious feed and clean water.
2. Rinse the oral cavity with astringent and antiseptic preparations.
3. Treat affected areas of the limbs and udder surgically.
4. Apply various therapeutic ointments, painkillers, and antibiotics.
5. Administer cardiac drugs if necessary, and intravenous solutions of glucose, calcium chloride, and sodium chloride.

Depending on the extent of the disease, various strategies are used to rehabilitate farms:

• Stamping out method: in countries free of foot-and-mouth disease (USA, Canada, England, Japan, Australia), all sick and suspected infected animals at an affected farm are destroyed, followed by disinfection of the site.
• Slaughter combined with vaccination: used in Western European countries to prevent further spread of the virus.
• Vaccination and strict quarantine: practiced in countries of Asia, Africa, South America, including our country. Healthy animals in the outbreak area are vaccinated with a preparation against the type of foot-and-mouth disease that has been registered in adjacent territories or poses a threat of introduction.

Upon detection of foot-and-mouth disease, a quarantine is imposed on the farm or settlement, and a threatened zone is defined. Restrictions are introduced on the export of livestock animals and agricultural products, a special procedure for their collection is established, and transport movement is temporarily prohibited. The quarantine is lifted 21 days after the recovery or slaughter of the animals, following mandatory final cleaning and disinfection of premises, exercise yards, equipment, and transport.

Tuberculosis of livestock animals: pathogen specifics and its survival

Tuberculosis is a chronic infectious disease of many species of agricultural, wild, fur-bearing animals, and poultry. It is characterized by the formation of specific nodules (tubercles) in various organs, prone to cheesy decay. The disease poses a general danger to livestock animals and humans: people can be infected with the bovine type of tuberculosis, and a sick person can infect cattle.

The causative agent of the disease is mycobacteria (genus Mycobacterium) — thin, straight, or slightly curved rods. Their cell wall contains fat-wax substances, providing high resistance in the external environment to physical and chemical influences. Three main types of the pathogen are known, each with its own range of susceptible hosts:

• Human type: humans are most sensitive; pigs, cats, dogs, cattle, and fur-bearing animals are also susceptible. Birds (except parrots) are insensitive to it.
• Bovine type: all agricultural and wild livestock animals, fur-bearing animals, and humans are sensitive. Birds are insusceptible.
• Avian type: birds and pigs are sensitive; other mammals and humans are infected by it extremely rarely.

• Quarantine period for foot-and-mouth disease — 21 days
• Immunity after foot-and-mouth disease — from 1 to 10 years
• Viability of mycobacteria in soil — more than 2 years
• Viability of mycobacteria in manure — 7 months

The high resistance of the tuberculosis pathogen requires strict control of its survival times in various farm objects and food products. The viability periods of mycobacteria must be taken into account when conducting veterinary-sanitary measures:

Object of the external environment or product	Duration of pathogen viability preservation
Manure	7 months
Dried cow feces	Up to 1 year
Soil	More than 2 years
River water	Up to 2 months
Meat (frozen)	Up to 1 year
Meat (salted)	45–60 days
Butter	Up to 45 days
Cheese	45–100 days
Milk	Up to 10 days

Heating milk to 70°C kills the tuberculosis pathogen in 10 minutes, and boiling in 3-5 minutes. The best disinfecting agents are:

• alkaline 3% formaldehyde solution (exposure 1 hour);
• bleaching powder suspension containing 5% active chlorine;
• 10% iodine monochloride solution;
• 20% fresh slaked lime suspension by three-fold whitewashing with an interval of 1 hour.

Epizootological data. Tuberculosis is most often registered in cattle, pigs, mink, and chickens; less often in goats, dogs, ducks, and geese; very rarely in sheep, horses, and cats. Monkeys are highly sensitive to tuberculosis. Among wild ungulates, marals are more prone to illness. Humans also suffer from tuberculosis.

The source of the infectious agent is livestock animals with tuberculosis, from whose bodies the pathogen is released with milk, feces, nasal discharges, and sometimes semen. When cows are infected with any type of tuberculosis pathogen, mycobacteria are always released with milk.

Livestock animals primarily contract tuberculosis through the alimentary route, but aerogenic infection is not excluded, especially when sick animals are kept together with healthy ones in enclosed, poorly ventilated, damp premises.

Tuberculosis among animals spreads relatively slowly. This is due to the long incubation period of the disease (up to 45 days). Inadequate feeding, unsatisfactory keeping conditions (overcrowding, dampness), and other adverse factors lower the overall resistance of the animal's organism and contribute to the rapid spread of the disease.

Course and symptoms. Tuberculosis usually follows a chronic course, and often without clearly visible signs. A positive reaction to tuberculin in animals occurs on the 14th-40th day after infection. Most animals sick with tuberculosis do not differ from healthy ones in appearance and general condition, especially at the beginning of the disease.

Sick animals are identified mainly through allergic and serological testing; tuberculous lesions are usually discovered only during post-mortem examination of organs. The appearance of clinically manifested forms of tuberculosis indicates a long-standing course of the disease.

Based on the localization of the pathological process, pulmonary and intestinal forms of tuberculosis are distinguished; lesions of the udder and serous membranes (pearl disease), a genital form, and generalized tuberculosis also occur. It is generally accepted to distinguish two forms of the disease:

• Open (active) tuberculosis, when the pathogen is released into the external environment with milk, feces, or sputum during coughing (in cases of intestinal, mammary gland, or uterine infection, the process is always considered open).
• Closed (latent) tuberculosis, in the presence of encapsulated foci without the release of the pathogen into the external environment.

In cattle, tuberculosis most often affects the lungs. With severe involvement, a slight increase in body temperature and an infrequent but strong cough are observed; with a protracted course of the disease, the cough becomes weak, soundless, but painful.

Pathoanatomical changes. Characteristic of tuberculosis is the presence of specific nodules (tubercles) in various organs and tissues of the animal, ranging in size from a millet seed to a chicken egg or larger. Tuberculous foci are surrounded by a connective tissue capsule, and their content resembles a dry, cheesy mass (caseous necrosis).

In ruminants, tuberculous lesions are more often detected in the lungs and thoracic lymph nodes. The lymph nodes are affected, becoming enlarged, dense, and tuberous, with caseous tissue decay in the center of the node. When serous membranes are affected, multiple dense, shiny tuberculous nodules, reaching the size of a hazelnut, are found on the pleura and peritoneum (pearl disease).

Organ	Cattle (%)	Pigs	Poultry
Thoracic lymph nodes	100	-	-
Lungs	99	-	-
Liver	8	rarely	90
Spleen	5	-	70
Udder	3	-	-
Intestine	1	-	rarely
Mesenteric and head lymph nodes	-	frequently	-
Bones	-	-	frequently

The diagnosis of tuberculosis is based on the analysis of epizootiological data, clinical signs, and the results of allergic, serological (complement fixation test with tuberculous antigen), pathoanatomical, histological, bacteriological, and biological studies.

Tuberculinization method. Two methods are used: the intradermal method — the main method of allergic diagnosis of tuberculosis in all species of mammals and birds (except horses) and the ophthalmic method (eye test) — used for diagnosing tuberculosis in horses. In some cases, this test is used in cattle simultaneously with the intradermal one, and sometimes the intravenous injection method is applied, followed by measurement of body temperature. Tuberculin (PPD and old tuberculin) — a purified product of the vital activity of Mycobacterium tuberculosis — is used as a diagnostic agent.

Injection site. With the intradermal method, tuberculin is administered: to cattle - in the middle third of the neck; to pigs - in the outer surface of the auricle, two centimeters from its base (avian tuberculin in one ear, bovine tuberculin in the other); to minks – intrapalpebrally (into the upper eyelid).

Timely diagnosis of tuberculosis allows preventing the spread of dangerous infection in the herd. The main method of control remains the allergic test using tuberculin. To obtain reliable results, it is important for the veterinarian to strictly follow the technique of administering the drug and the timing of reaction assessment.

1. Clip the hair at the injection site and clean the skin with 70% alcohol.
2. Administer the tuberculin using a needleless injector or a syringe with a special needle.
3. Assess the reaction in cattle after 72 hours, and in pigs — 48 hours after the administration of the drug.

A positive reaction is determined by the appearance of inflammatory swelling at the injection site — it can be diffuse or clearly contoured, doughy or dense, painful or painless. In cattle, a sign of a positive reaction is the thickening of the skin fold by 3 mm or more compared to the thickness of healthy skin adjacent to the injection site. In pigs, the reaction is considered positive upon the formation of swelling at the injection site; in minks — upon swelling of the eyelid.

For routine herd monitoring, allergic tests are conducted annually according to a schedule. Breeding cattle are tested twice a year, while the rest of the cattle population is tested once a year, starting from 2 months of age. Sows, boars, and, if necessary, young pigs are checked once a year from 2 months of age. Welfare monitoring in poultry and fur farms is carried out using the allergic method and pathological examination of dead or slaughtered animals. Horses, mules, donkeys, and sheep are tested only in farms affected by this disease.

Quarantine restrictions, disinfection rules, and product processing

When tuberculosis occurs, the farm is declared affected, and quarantine restrictions are imposed. Reacting cattle and buffaloes are isolated and sent for slaughter within 15 days, while young animals born to infected dams are fattened in isolation and also sent for slaughter. Other animals on the affected farm that did not react to tuberculin are retested according to an approved scheme until negative results are obtained.

Stage of testing for non-reacting animals	Interval of performance
Initial monitoring until two negative results are obtained	Every 30–45 days
Control tests before lifting restrictions	Twice with an interval of 3 months

Routine disinfection of livestock premises, exercise yards, and equipment is carried out once a month after each animal test. Manure must be disinfected, and the top layer of soil on the farm is treated. Milking machines and dairy utensils are washed daily and treated with a jet of hot steam. In disease-free farms, animals and feed are purchased only from clean zones, new livestock are kept in a 30-day quarantine, skim milk for feeding young animals is pasteurized, and people suffering from tuberculosis are not allowed to work.

• Alcohol for skin treatment — 70%
• Quarantine for new animals — 30 days
• Slaughter of reacting cattle — within 15 days
• Dose of isoniazid for mink — 10 mg/kg for 75 days
• Vaccination of mink pups with BCG — at the age of 20–30 days
• Duration of BCG immunity in mink — 68 months