Leptospirosis is caused by the bacteria Leptospira interrogans. There are over 150 serovars of L. interrogans, of which six are found in NZ. The serovars Leptospira hardjo and Leptospira pomona are the two most commonly associated with sheep. Surveys have shown that leptospirosis is very common in sheep and over 90% of flocks have antibodies to L. hardjo and over 70% to L.pomona.
L. hardjo causes virtually no symptoms in sheep but L. pomona is known to cause clinical disease. Disease is often associated with wet conditions and the presence of pigs (pigs are the maintenance host for L. pomona).
Disease in hogget's: In an outbreak situation some lambs will be found dead and others will be lethargic and not eating. They may have red coloured urine that often stains the wool on the hocks and crutch area and there may also be pale, muddy coloured or yellow mucus membranes due to jaundice. On post mortem the carcase may be jaundiced (yellow), the kidneys are often dark with haemorrhage and white spots present on the surface. The urine in the bladder may be the colour of blood (haemoglobinuria). Diagnosis is often made from histological findings and from serum antibodies levels in blood samples, taken from sick animals.
Treatment of sick animals with antibiotics is highly recommended along with the vaccination of all in-contact animals.
HUMAN RISK
Humans are very susceptible to leptospirosis. Both L. hardjo and L. pomona can cause disease ranging from mild flu like symptoms to severe disease requiring hospitalisation. Symptoms can last for a long time and may recur.
In New Zealand it has been shown that leptospirosis in humans is severely under reported with an estimated 45 fold under-reporting rate1.
The highest risk occupations are meat workers (often those on sheep chains) and farmers.
References:
Cord Heuer, Jackie Benschop, Leslie Stringer, Julie Collins-Emerson, Juan Sanhueza, and Peter Wilson A Report by Massey University Prepared for the Zealand Veterinary Association June 2012
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