Leptospirosis is transmissible to man and represents an occupational hazard to veterinarians, abattoir workers, dairy and pig farmers.

The most commonly encountered serovars associated with clinical disease are:

Other serovars do affect domestic animals in Australia, particularly Northern Australia, but such infections are rare in NSW.

Zoonotic infections are usually acquired from the maintenance host for each serovar:

In the maintenance host, infections by these specific serovars are likely to be endemic, whereas serovar infections in non maintenance hosts are usually associated with sporadic outbreaks of disease. The most common manifestations of leptospirosis in animals are:

• Abortion - all species
• Milk drop syndrome/ mastitis - cattle
• Pyrexia/septicaemia - all species
• Icterus and/or haemoglobinuria - mainly dogs and calves
• Kidney lesions found at routine slaughter - pigs, cattle
• Mortalities following pyrexia and/or icterus/haemoglobinuria

Diagnosis

Serology (Microscopic Agglutination Test). Confirmed by demonstration of leptospires via direct microscopic examination of urine or foetal fluids (thoracic, peritoneal, pericardial); and/or by demonstration of organisms in kidney by histopathology.

In general culture of tissues, foetal fluids, urine or milk is not undertaken, except under specific arrangements with the receiving laboratory.

Specimens required

Abortion

Samples as outlined in Abortion in cattle or Abortion in swine. Whenever possible, submit serum from dam, including 10-15 sera from cohorts, and fresh, chilled entire foetus with membranes (or chilled and fixed foetal tissues, including serous fluids) for bacteriology and histopathology.

Milk drop syndrome

1. Serum samples from 10-15 affected and recovered cases and cohorts, submitted chilled for serology.
   • A convalescent serum sample collected 10 days or more after agalactia often shows a rise in titre to L hardjo.
2. Sample of urine preserved with formalin (approx. 1 ml of 10% neutral buffered formalin to 99 mls urine) added immediately after collection, from both affected and recovered cases, for dark ground microscopy. It is worthwhile using a diuretic to obtain a sample with large numbers of organisms and minimal contaminants.
3. Samples of milk for differential diagnosis of mastitis, submitted as outlined in Mastitis.
4. In certain cases, following consultation with the Regional Veterinary Laboratory, arrangements may be made to sample cows for culture and PCR. This involves field-inoculation into selective liquid media of mid-stream urine collected after diuretic treatment.

Pyrexia

1. Serum samples from 10-15 affected and recovered cases and cohorts, submitted chilled for serology.
2. Sample of urine preserved with formalin (approx. 1 ml of 10% neutral buffered formalin to 99 mls urine) added immediately after collection, from both affected and recovered cases.

Icterus/Haemoglobinuria

Samples as for "Pyrexia", but do not collect urine for microscopic examination from animals affected with haemoglobinuria. Urine shedding of leptospires occurs after the haemoglobinuric phase.

Kidney lesions in slaughter animals

1. Portions of affected kidneys in buffered formalin for histopathology.

Mortalities following following pyrexia and/or icterus/haemoglobinuria

1. Sections of liver and kidney, in buffered formalin for histopathology.

Interpretation of results

Interpretation of Leptospiral titres

For the MAT, titres are given which reflect the standard Leptospiral dilution series for sera. For leptospiral MATs, this is a doubling dilution series starting at 1:25 (L hardjo) or 1:50 (other Leptospires).

In cattle, an MAT titre to L hardjo of 25 or greater may be significant. Indication of current infection can only be gained by demonstrating at least a four-fold (i.e. 2 dilution) increase.

Titres following vaccination are generally low (less than 400) and do not persist. In cases of abortions in cattle due to L hardjo, titres at the time of abortion may be equivocal and falling.

In L pomona infections and L hardjo milk drop syndrome, titres generally rise within 1-3 weeks of the appearance of clinical signs. L pomona is more immunogenic than L hardjo, so titres to L pomona are often 800 or more, whereas in L hardjo milk drop syndrome, they may be less than 800. L hardjo titres of 200 or more are generally significant.

Submission of 10-15 sera from animals in the same group as the affected individuals will give a more accurate assessment of the leptospirosis status of the herd. To determine recent infection, 10-15 paired sera (taken 2-4 weeks apart) should be submitted to detect rising titres (along with the clinical history of the tested animals). In an endemically infected herd at any given time, some titres will be rising, some will be static, and others will be falling.