Anthrax, Biology

Anthrax

It is also known as spleenic fever. The peracute form of the disease in animals is manifested by sudden death with oozing of dark-coloured blood from body openings.

Etiology: The disease is caused by gram positive spore forming bacilli Bacillus anthracis. It has zoonotic importance as human beings suffer from "Wool sorter 's disease".The disease has been reported from throughout the world resulting in high morbidity and mortality rates.

Pathogenesis: The deaths are caused due to shock, acute renal failure and terminal anoxia.

Clinical signs : In cattle, buffaloes and sheep, disease occurs in peracute or acute form. In peracute form, the animals die suddenly, within 2 h of bleeding from mouth, nostrils and anus. Before death, these animals suffer from fever, muscular tremors, dyspnoea and convulsions. In acute disease, the animals survive for 3-4 days and reveal hyperpyrexia, depression and edematous swelling of tongue, throat and flank areas. Respiration and heart rates are elevated while ruminal movements are absent. Visible mucous membranes are congested with haemorrhagic spots on them. In horses, disease occur in acute form and show hyperpyrexia, depression and dyspnoea. If the organisms are ingested, they suffer from enteritis and colic. Pigs suffer from acute or subacute form of the disease and reveal temperature rise, anorexia, swelling of throat and face, dysentery and blood tinged froth. The skin may have petechial haemorrhages.

In human beings, skin infection is more common resulting into ulcerations of skin. However, if the organisms are inhaled, they show lobar pneumonia, exudative pleurisy and death.

The carcass is not to be opened if death is suspected due to anthrax. However, the organisms can be seen in the blood or edematous fluid. Typical postmortem lesions are presence of dark-coloured, unclotted blood, absence of rigor mortis, rapid carcass decomposition, presence of echymotic haemorrhages on whole body and soft, liquefied, enlarged spleen.

Diagnosis: The disease is diagnosed by history and its typical symptoms and confirmed by isolation of organisms from blood or edematous fluid. Blood (2 ml) from suspected cases can be injected subcutaneously in guinea pigs resulting in death in 2-3 days. Ascolis test can be performed for its confirmation by preparing antigen from piece of ear or spleen of infected animal and then performing immunodiffusion test.

The disease has to be differentiated from peracute black quarter, lead toxicity, acute leptospirosis and bacillary haemoglobinuria. Peracute form of black quarter reveals crepitating swelling, while in lead toxicity, nervous symptoms are more pronounced. In acute leptospirosis and bacillary haemoglobinuria, presence of haemoglobinuria is a consistent finding.

Treatment: Anti-anthrax serum along with broad-spectrum antibiotics can be used for treatment. Antiserum is given @ 100-250 ml by intravenous route. Penicillin (10,000 units/kg body weight), streptomycin (8-10 g) or oxytetracycline (5 mg/kg body weight) given twice daily by intramuscular route for 4-5 days is effective.

Control: The carcass should be buried deep with sufficient lime. For cleaning of floor and other materials, 5-10% NaOH or formalin may be used. KMnO4 (4%) kills the spores in 30 min. Live anthrax spore vaccine is available which is given @ 1 ml subcutaneously in all the animals.

Posted Date: 9/19/2012 1:32:12 AM | Location : United States







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