Animal tuberculosis: diagnosis and prevention

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Tuberculosis is a severe chronic disease affecting humans and many animal species. It is characterized by tubercles - specific nodules that form in different organs, followed by caseous necrosis and calcification. The topic of today's article is animal tuberculosis (symptoms and treatment).

What is this disease?

She has been known since ancient times. The description of its signs is found in the writings of Hippocrates as early as the 4th century BC. e. In 1882, R. Koch succeeded in solving the problem of identifying the causative agent of this serious illness, and a little later, he also produced tuberculin. The BCG vaccine appeared in 1924 and still serves as a specific prevention of human tuberculosis.

Animal TB occurs in most regions. We can talk about its almost complete elimination only in developed European countries and the United States. Due to this disease, animal husbandry suffers significant economic losses, which is associated with a drop in productivity, unplanned culling and sending sickindividuals for slaughter, as well as the need for serious costs for expensive anti-epidemic measures.

Who is the causative agent

Mycobacteriumtuberculosis - under this name there is a mycobacterium, in the genus of which there are over 30 different types of microorganisms. Some of them are non-pathogenic, others are pathogenic, that is, capable of causing disease. Three of the latter are particularly dangerous.

The human species leads to disease in humans. In addition, dogs, cats, pigs and cattle are susceptible to it. It is also capable of hitting fur-bearing animals. Birds (with the exception of parrots) are not susceptible to it.

The type of tuberculosis called bovine is capable of causing tuberculosis in animals and humans. Moreover, not only agricultural livestock, but also wild animals are subject to it. Only birds remain immune in this case.

A bird species can also affect pig stock. Cases of infection in humans or other animals are very rare.

Tuberculosis bacilli (mycobacteria) of each of the listed species are quite similar. They can be found in smears in groups or singly. In addition to tuberculosis, there are also conditionally pathogenic mycobacteria. If they infect animals, a similar reaction to a specific sample is possible, which can make it difficult to diagnose tuberculosis in animals.

The resistance of mycobacteria to chemicals and various external factors is very high. In soil or manure, it can be stored inviable form for up to 4 years or more. The corpses of cattle and dead birds serve as a repository of mycobacteria from 3 months to up to a year. For a sufficiently long time, the causative agent of animal tuberculosis can exist in products (milk, butter, cheese, meat) obtained from sick animals.

Which animal is more likely to get TB?

Most wild and domestic fauna are susceptible to it (over 55 species of mammals and 50 species of birds). Hypersensitivity to animal tuberculosis is typical for cattle and pigs, as well as chickens. Much less often, cases of the disease occur in cats, dogs, geese and ducks, and only as an exception - in sheep, horses and donkeys.

The source is considered sick animals, the release of mycobacteria from the body of which occurs with milk, sputum, feces. Once in the body, the pathogen is able to persist in an undetectable form for a long time. Such individuals can serve as hidden sources of disease.

What are the main causes of animal tuberculosis? Once in certain conditions, this form of mycobacteria reverses into its classical form and leads to the onset of the disease.

Distribution routes

Tuberculosis of farm animals is transmitted through feed, water, bedding, contaminated with secretions of already sick individuals. The defeat of young animals occurs mainly through milk. From a sick mother, calves can become infected in utero. Cases and transmission of tuberculosis through contact with sick people are not excluded(calves, milkmaids). In the stall period, the route of infection of adult cattle is aerogenic. Transmission of the pathogen in open pastures is possible in summer.

The defeat of pigs is possible in the process of feeding kitchen waste obtained in hospitals and tuberculosis dispensaries and not subjected to disinfection. The way cats and dogs are infected is when they eat milk or meat from sick cows.

The resistance of the animal organism is an important factor influencing the rate of mass spread of the disease. With its decline, the epidemic can take on alarming proportions. This happens in cases of inadequate feeding, lack of important trace elements, amino acids and vitamins in the diet, a small amount of exercise, dampness and cramped premises and unsanitary conditions.

How disease occurs

Having entered the body by air or feeding, Mycobacterium tuberculosis of animals find themselves in the lungs or other organs with the blood or lymph flow. In the places of their localization, inflammation and the formation of tubercles (tuberculous nodules) occur. They are round and greyish in color and about the size of a lentil seed.

Dead cells inside the tubercles take the form of curdled mass. If the disease proceeds benignly, the primary focus is calcified and, surrounded by connective tissue, does not lead to the progression of the disease. In cases of reduced resistance, the walls of the tuberculous nodule let mycobacteria into the external environment. Once in he althy tissues, they formmany other similar foci and sometimes merge into entire large areas affected by tuberculosis.

Getting out of them into the blood, mycobacteria spread to various organs, in which foci of various sizes appear. In the case of extensive lesions, the disease easily leads to exhaustion and death.

How to detect tuberculosis in animals

The incubation period of this disease is 2-6 weeks. Due to the possible latent or chronic course of the disease, it is possible to detect the first clinical signs of a lesion only months or even years after infection. Diagnosis of tuberculosis in animals exists mainly in the form of one of two methods - allergic and serological. Clinically expressed forms already speak of a fairly long course of the disease. They can be diverse even among representatives of the same species.

The pathological process can be localized in the pulmonary or intestinal form, as well as some others. There may be cases of generalized tuberculosis. With the defeat of the lungs in cattle, most often the course of the disease is chronic. Acute and subacute developmental variants are found in young animals.

Tuberculosis in animals - symptoms

It is possible to determine the disease in the lungs in animals by a dry, strong cough, aggravated when standing up or in cold air. An increase in temperature is possible up to 39.5-40 ⁰С. Productivity, like appetite, does not decrease at the initial stage.

When the disease progresses, signs can be founddamage to the lungs and pleura. Cough becomes painful, breathing becomes difficult. When listening in the chest, wheezing is observed.

If the mammary gland in cows is affected, one can observe an increase in the lymph nodes above the udder with the formation of dense and inactive tubercles. Milk is obtained in the form of a curd mass or with impurities of blood. In the case of generalized tuberculosis, there is an increase in tuberous lymph nodes located superficially.

Pigs can get sick almost asymptomatically. In the case of extensive lesions, vomiting, difficulty breathing and coughing can be observed. In relatively rare cases of goats, sheep and horses, symptoms are rarely pronounced. In the case of a severe clinical picture, the signs are similar to those described above.

Birds (ducks, geese and chickens, turkeys) suffer from tuberculosis in a chronic form. In this case, there are usually no obvious clinical signs. You can determine the disease in chickens by inactivity and thinness. Combs and earrings in birds take on a pale color and wrinkle, pectoral muscles atrophy. Most often, birds die as a result of exhaustion.

Few characteristic signs can also be observed in cats, dogs and wild fur animals. Similarly to birds, exhaustion, coughing and difficulty in the respiratory process (with lung damage) are observed. The weakening of the body leads to death.

Diagnostic Methods

Mainly produce a study on tuberculosis of animals of an allergic nature with the help of intraderm altuberculin test. The drug is injected into the middle of the neck of cattle, pigs - near the outer surface of the ear, goats - into the lower eyelid, fur-bearing animals and dogs - into the surface of the thigh. Wool is cut out before injection, feathers are plucked from birds. The skin is treated with ethyl alcohol.

After 72 hours, evaluate the reaction to tuberculin. In unfavorable situations, repeated administration of the same dose is acceptable. When thickening the skin, measure the thickness of the fold in millimeters and compare with the unchanged area.

If certain normative figures of such thickening (from 3 mm or more) are exceeded, the animal is considered to be responsive to tuberculin. In this case, the general immunoreactivity of the organism should be taken into account. The reaction may be mild in individuals of low fatness, old and weakened.

A small number of animals with the most striking signs are slaughtered. Some tissues are sent for bacteriological examination to a veterinary laboratory. You should be aware that in the case of a positive diagnosis, phagocytosis is incomplete. The immunity generated by this does not serve as a measure of further protection.

As in humans, animals can be prevented by the BCG vaccine. However, this practice is not accepted in most countries.

Prevention of tuberculosis in animals

Can any early action be taken? They are regulated by the current sanitary and veterinary rules for animal tuberculosis. Households classified as prosperousare completed with he althy individuals with the acquisition of the same feed. All incoming livestock is subject to a 30-day quarantine with a study on tuberculosis. Food waste is treated thermally. Serving animals to people with tuberculosis is not allowed. Premises for keeping livestock are periodically disinfected, ticks and rodents are destroyed in them. The quality of feeding and other conditions of detention are monitored.

In order to prevent tuberculosis in animals, a planned annual study of livestock for this disease is provided. Cows and bulls are inspected twice a year - before spring pasture and in autumn, by the time they are put into winter keeping. Young growth is checked from two months of age annually. Other animals - depending on the existing danger of the epidemic. At the same time, it is supposed to examine animals belonging to private owners.

Is treatment possible?

Sick farm animals are not treated. They are taken for slaughter. If the presence of a disease is established in a settlement (on a farm, in a herd), any animal that reacts to tuberculin is recognized as sick. It should be sent for recycling within two weeks.

If we are talking about a prosperous economy, individuals that respond to tuberculin are subjected to additional studies by ophthalmic or intravenous testing for tuberculin. In the case of a positive reaction, a control slaughter is carried out with the study of the obtained material in a veterinary laboratory. Having discovered, as a result of a bacteriological test, the fact of a lesiontuberculosis of animals, the entire farm is declared unfavorable for it with all the relevant restrictions, as well as with the preparation of an action plan for recovery.

According to the scale of the spread of the disease, different degrees of trouble are classified. It is considered limited when the number of sick animals detected using a double test for tuberculin is no more than 15% of the total population. If this figure is exceeded, the degree of distress is considered significant.

He althier farm stock

How is the improvement of the herd of cattle recognized as unfavorable? The methods for this are as follows: isolation of sick animals or their groups with subsequent destruction, or a one-time replacement of the entire livestock with a he althy herd. In both cases, a whole range of veterinary and sanitary measures is required. According to the instructions, the premises freed from sick livestock are disinfected with sanitary repairs. Pastures grazing with diseased animals are used only after 2-4 months in various regions of the country.

Restrictions on dysfunctional farms can only be lifted after the full completion of all sanitary measures with final disinfection and mandatory laboratory quality control of the latter.

If the disease is limited, the herd is healed through systematic research, selection and slaughter of diseased individuals. Tuberculin tests are done intradermally to all cattle from age2 months with a regularity of 45-60 days. Other animal farms, including dogs and cats, are also subjected to simultaneous testing for tuberculosis. Individuals that have reacted to tuberculin are recognized as sick. They are subjected to isolation and surrender within 15 days for slaughter.

If tuberculosis is found in a poultry farm, all poultry belonging to a dysfunctional workshop (poultry house) is subject to slaughter, followed by veterinary and sanitary measures. After the restrictions are removed, a new herd is formed from he althy young animals. Eggs obtained from birds of a workshop or poultry house recognized as unfavorable are not allowed for incubation or use in the confectionery industry and when baking bread.