Leptospirosis - Cattle and Sheep

Description

Leptospirosis is an economically significant zoonotic disease caused by the bacteria Leptospira interrogans. Disease in cattle is usually due to L.pomona or L.hardjo; L. interrogans serovar hardjo is host-adapted to cattle, whereas L.pomona is non-host specific. Clinical disease is rarely seen in sheep; they are less susceptible to the bacterium but may act as non-symptomatic carriers.

In cattle leptospirosis is seen in 3 forms, acute, subacute and chronic. The acute disease is seen most frequently in calves, causing pyrexia, haemoglobinuria, icterus, anorexia, uraemia due to renal damage and death. Acute disease in susceptible heifers is seen as fever, lethargy and agalactia of all quarters; abortion and stillbirth may also occur. The subacute form results in clinical signs similar to those of the acute disease, in a less severe form. The main signs of the chronic or enzootic form are infertility, especially in heifers, and abortions. An abortion storm is a common presentation of leptospirosis, with several cattle aborting at the same time, typically 4-12 weeks after the initial infection.

In the rare cases affecting sheep, infection results in an acute syndrome in lambs, or abortion and agalactia in ewes.

Signalment

Risk factors include access to rivers and watercourses, rodent infestation, buying in stock and using a bull instead of AI. Co grazing sheep with cattle can result in disease in cattle as sheep can act as non-symptomatic carriers.

A high percentage of UK herds are infected with leptospirosis, it is estimated that 75% of UK cattle have been exposed to the disease.

Diagnosis

Clinical Signs

Acute syndrome:

• Pyrexia
• Anorexia
• Dyspnoea
• Haemolytic anaemia
• Icterus
• Haemoglobinuria
• Changes in milk

Subacute form:

• Lethargy
• Pyrexia
• Flaccid udder
• Changes in milk
• Abortion, still births or weak calves

Enzootic/chronic form:

• Abortion
• Infertility
• Milk drop

Laboratory Tests

Leptospirosis can be diagnosed by rising antibody titre in paired serum samples in the acute and subacute forms, however in the chronic form the initial infection may not be obvious and serology is not useful if the disease is enzootic in the herd.

Culture on special media and fluorescent antibody techniques on tissues can be used to demonstrate the causative organism.

In dairy herds, a bulk milk sample will give an indication of the disease status of the herd.

Pathology

In the acute form of the disease anaemia and icterus are usually obvious. On post mortem examination the kidneys are swollen and dark, with ecchymoses and petechecial haemorrhages. The liver may be pale, swollen and friable with areas of necrosis. Lesions may be seen in other organs depending on the serovar of Leptospira.

Treatment

Treatment in acute cases is supportive in conjunction with antibiotics. A blood transfusion may be necessary if haemolytic anaemia severe in calves; oxytetracycline, tetracyclines, enrofloxacin and erythromycin may all be effective if administered early enough.

Chronic infections can also be treated with antibiotics; oxytetracycline, enrofloxacin and ampicillin are all effective.

Management of infected herds depends on whether it is a beef or dairy herd. It is worth vaccinating and treating all cattle with prophylactic antibiotics in a beef herd if leptospirosis is diagnosed in the early stage in order to protect the herd. In a dairy herd the milk withdrawal due to treatment with antibiotics makes this option uneconomical, and therefore treatment is usually limited to the affected animals.

Vaccination will reduce the incidence of the disease and improve fertility in the herd. The initial course is 2 doses 4-6 weeks apart; protection is maintained by yearly boosters.

References

• Divers, T.J. and Peek, S.F. (2008) Rebhun's diseases of dairy cattle Elsevier Health Scieneces
• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
• Radostits, O.M, Arundel, J.H, and Gay, C.C. (2000) Veterinary Medicine: a textbook of the diseases of cattle, sheep, pigs, goats and horses Elsevier Health Sciences