Exercise 22. Test yourself by answering these questions to see how much you remember and understand.

1. What kind of disease is bovine TB? What is its causative agent?

2. Which species are susceptible to bovine TB?

3. In case of bovine TB, what does infection progress depend on?

4. Is bovine TB difficult to diagnose? Which test is used by veterinarians to make a diagnosis?

5. What are the clinical signs of bovine TB in the early stages? … later stages?

6. What do you know about infection transmission from animal to animal?

7. How can infection be transmitted to people?

8. What do you know about treatment and control of this disease?

TEXT D

BLACKLEG

VOCABULARY LIST TO TEXT D

Blackleg is an acute, febrile,highly fatal diseaseof young cattle and sheep caused by the spore forming, rod shaped, gas producing bacteria Clostridium chauvoei. The disease is found worldwide. The spores of the organism can live in the soil for many years and are considered the main source of infection. Outbreaks of blackleg have occurred in cattle on farms in which recent excavations have occurred or after flooding. The disease usually occurs in summer and fall and is uncommon during the winter. Commonly, the animals that contract blackleg are of the beef breeds, in excellent health, and gaining weight. The bacterium enters the body by ingestion (through food) and then makes small punctures in the mucous membrane of the digestive tract and thus gains entrance to the bloodstream. The bacterium, which causes the disease, commonly affects the heavy muscles and other tissues (spleen, liver, and alimentary tract). The disease is not transmitted directly from sick animals to healthy animals by mere contact.Young cattle, rapidly gaining weight, between 6 months and 2 years of age, are most susceptible to the disease.In cattle, blackleg infection is endogenous. Lesions develop without any history of wounds. But in sheep, the disease is almost always the result of a wound infection and often follows some form of injury such as shearing cuts, docking, or castration. The spores of the bacterium might be present in the gut of the animal for sometime. These spores do not immediately result in the disease. Medical research is ongoing to find what conditions cause these ingested spores to give rise to the disease.This is the danger of blackleg. Seemingly-healthy cattle and sheep can be infected without showing any outward signs.

The onset of the disease is sudden, and a few cattle may be found dead without premonitory signs. Acute, severe lameness and marked depression are common. Initially, there is a fever but, by the time, clinical signs are obvious, body temperature may be normal or subnormal. Characteristic swellings develop in the hip, shoulder, chest, back, neck, or elsewhere. At first, the swelling is small, hot, and painful. As the disease progresses, the swelling enlarges and becomes spongy and gaseous. If you press the swelling, gas can be felt under the skin and these swellings make a cracking sound under pressure. The animal usually dies in 12 to 48 hours. In most cases, the animal is found dead without being previously observed sick. The speed with which blackleg kills usually makes individual treatment useless. However, in the early stages of blackleg, treatment with penicillin or other antibiotics in large doses is helpful. The cattle, which recover from this disease, may have a weak muscle in legs, shoulder and other parts of the body.

Blackleg is almost entirely preventable by vaccination. The most commonly used clostridial vaccination in cattle is the 7-way type which protects against Clostridium chauveoi (blackleg), Clostridium septicum and Clostridium sordelli (malignantedema), Clostridium novyi (black disease), and three types of Clostridium perfringens (enterotoxemia). The best way of preventing more instances of Blackleg will be by revaccinating animals. Burning the upper layer of soil to eliminate spores with oil or straw also works well.

EXERCISES TO THE TEXT

Exercise 23.Look through the text and find information about:

-causative agent of blackleg;

- parts of the world where blackleg is common;

- animals that are susceptible to blackleg;

- season when blackleg outbreaks are most common;

- the way bacteria enter the body;

- clinical signs of blackleg;

- main ways of infection transmission;

- treatment and prevention of blackleg.