DISEASE RISK MANAGEMENT: BOVINE TB - THE FACTS PART 2
BOVINE TB - THE FACTS PART 2
The Diagnosis of Bovine TB
The diagnosis and confirmation of Bovine TB must be carried out by a professional veterinarian where an animal’s history, clinical signs and geographical location must be taken into consideration.
Bovine TB may only present symptoms in animal years after infection has occurred. Where no symptoms are present the tuberculin test (skin test) may be carried out where animals are thought to be infected or if there is an outbreak of the disease in a specific geographical area.
Other methods of diagnosis may include:
Smears – these are made up of mucous which is coughed up, from the solid segment of centrifuged milk and urine, from sheath secretions, from dung or from lymph nodes and other organs. These smears are stained according to the Ziehl-Neelsen method and examined under an optical microscope.
The Intradermal Bovine Tuberculin Test - this test is most often conducted to trace bovine TB infection in cattle and buffalo. Results are based on the sensitivity that develops in the body after infection with Bovine TB. A delayed hypersensitivity reaction, in which a swelling develops in the skin, means a positive answer. There are however numerous several factors which may lead to a false negative result, due to this, the intradenal bovine tuberculin test is generally combined with the avian tuberculin test for accurate results. When combined the bacteria may cause pathological changes and visible lesions indicating an accurate and reliable positive result.
NOTE: Conducting a tuberculin test In South Africa is subject to government approval and specific conditions.
Other tests which can be carried out include:
The Temperature Test,
The Double Intradermal Test and
The Stormont Test
Advanced tests include:
The Polymerase Chain Reaction (PCR) Test or
The Enzyme-Linked Immunosorbent Assay (ELISA) Test
Symptoms of Bovine TB
Where tubercles are scattered internally an animal may become emaciated with an inconsistent appetite fluctuating body temperature and a dull coat. These animals may become weak and listless even when their eyes remain clear. Symptoms will become more pronounced when the body is subjected to stress or increased demand such as when calving.
When a suppressed, moist cough is heard early in the morning, after running or when temperatures drop, an animal may have an advanced lung infection caused by Bovine TB. Breathing may become laboured and the animal emaciated as the disease spreads and enlarged lymph nodes constrict airways and the oesophagus. Bloating may occur as a result of the blocked oesophagus. Enlarged lymph nodes may also obstruct the digestive system leading to constipation or diarrhoea. Enlarged superficial lymph nodes will be visible and can be felt.
A Bovine TB uterine infection may obstruct conception or lead to abortion at an advanced stage of pregnancy. This type of Infection poses a risk to a calf as it can be passed through the udders. Mastitis can be caused by other organisms making Bovine TB mastitis particularly hard to identify visible symptoms one should look for include hardening or enlargement of the upper section of the udder quarters as the lymph nodes will have grown. These lymph nodes, if present without tangible lesions indicate Bovine TB is present. The animal’s milk will also appear normal however in advanced stage of the disease this milk will become a light yellow/brown colour as well as being watery.
The Economic Risk Of Bovine TB
In 1911 Bovine TB was declared a controlled disease in South Africa. It is classified by the World Organisation for Animal Health as a notifiable animal disease with specific impact on international trade.
Economic loss occurs due to high mortality and low reproduction rates in cattle farms and game breeding facilities as well when a restriction of trade is implemented on export to countries which are currently Bovine TB free.
The Control And Prevention Of Bovine TB
In terms of the Animal Diseases Act of 1984 and its accompanying regulations Bovine TB has been declared a controlled disease. Apart from requiring compulsory notification of the disease, the regulations also make testing compulsory in geographical areas where the disease occurs or is suspected. Regulations in this act can call for an imposed quarantine or culling of all animals in an area where animals are infected with Bovine TB.
Numerous testing schemes, which include accreditation and the diagnostic herd testing scheme have been developed to help trace, control, combat and in the hopes of eventually eradicating this disease.
Farmers and Game Breeders should frequently consult the local state veterinarian about new methods and ways of preventing and controlling Bovine TB. As yet no effective vaccine has been developed to prevent bovine TB.
Given the importance of making sure that our buffalo remain free of any such diseases we at Purple Rain, in conjunction with our partner, Poon Liebenberg Wildlife, go to great lengths to ensure that we remain ahead of the biosecurity curve. This is achieved by securing our camps with double fencing to combat contact with other animals and to diligently test our animals on a regular basis.
Resources
*Wikipedia - Mycobacterium bovis
*TBFree NewZealand
*cfsph
*Farmers Weekly
