Colibacillosis of newborn animals, Biology

Colibacillosis of newborn animals


This is the commonest disease entity of newborn farm animals. In calves the disease  occurs in three forms, viz. enteric colibacillosis manifested by diarrhoea, septicaemic colibacillos is manifested by bacteraemia and sudden death, and enteric-toxaemic colibacillosis also characterized by sudden death but without significant bacteraemia. The causative agent is Escherichia coli which is a gram-negative bacillus, aerobe and facultative anaerobe. Many strains are motile. Under natural conditions the organism may survive for weeks or months in water, faeces and dust in animal houses. E. coli is a natural inhabitant of intestinal tract of healthy calves and other animals. Colibacillosis is caused due to rapid multiplication of certain serotypes of E. coli. The conditions under which certain serotypes multiply rapidly are not known. The adult animals develop antibodies against E. coli. In young calves the colostrum inhibits the abnormal rate of multiplication of the organisms. For this reason, it is important to feed the calf with colostrum in first 48 hours of life.


Transmission: Colibacillosis can be rapidly produced in calves and piglets by feeding first milk infected with pathogenic strain of organism. The source of infection is the faeces of infected animals. The piglets show signs of illness after 24 hours of birth and the organism are derived from bedding rather than uterus and vagina of sows. In foals the infection is regarded as intra-uterine in most cases. Ingestion is the most likely portal of entry in other species, although infection via the navel and naso- pharyngeal mucosa can occur.


Symptoms:
Three distinct forms of disease have been identified in calves but one form may follow the other in an individual animal. In enteric-toxaemic colibacillosis newborn animals die between 3 and 6 hours. The clinical signs are coma, subnormal temperature, irregular heart and no scouring. The septicaemic collibacillosis is most common in calves during the first 4 days of life. The disease is acute and there is no diagnostic clinical sign. The enteric form of disease occurs chiefly during the first 3 weeks of life and particularly during first week. The faeces is watery or pasty, chalk white to yellow, may be mixed with blood and have an offensive rancid smell. Usually temperature rises up to 40.50C.

The lambs manifest enteric signs and some animals may become chronic. Most of the animals show septicaemic or peracute symptoms. Lambs 1-2 days and 3-8 weeks old suffer from disease. Acute cases collapse without showing any symptoms but a few animals show signs of acute meningitis by stiff gait and tetanic convulsions. In chronic cases the signs of arthritis are manifested.The piglets are born healthy but illness starts after about 24 hours. Some animals die without showing symptoms and others show profuse diarrhoea. Animals are weak and show subnormal temperature. Most of them die within 24 hours of onset of disease.


Lesions: Significant lesions may be absent, but in those which have died of colisepticaemia there may be subserous and submucosal petechial haemorrhages and enteritis. In cases of pneumonia the lungs may show areas of congestion and necrosis. The spleen and lymph nodes of mesentery are sometimes enlarged and congested, and joint infections develop as synovitis.


Diagnosis: Aseptic culture of heart blood, bone marrow and other clinical material is useful in diagnosis of septicemic diseases. The organisms can be cultured from  intestinal contents, urine, milk, vaginal exudates and grows easily on tryptose blood agar and MacConkey agar incubated at 37°C for 24 hr. Deoxyribonucleic acid (DNA) probes and polymerase chain reaction (PCR) assays have been developed to detect virulence factor gene.


Treatment
: Antiiotics like  step to mycin, tetracycline s, neo mycin  and chloramphenicol are effective against E. coli. Although the sensitivity to different strains varies widely. Some of the strains now show multiple drug resistance and it becomes difficult to treat those animals suffering from such strains. It is advisable to carry out drug sensitivity before the treatment is started.


Control: The most important control measure in neonatal colibacillosis is feeding of adequate colostrums to neonates. Control also depends upon improved sanitation, hygiene, decreasing density of crowding, proper housing with adequate ventilation and sunlight in the buildings. Vaccination of calves and piglets with bacterins or of the dams 2-4 weeks before calving or farrowing is not of much value.

Posted Date: 9/17/2012 6:31:46 AM | Location : United States







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