Leptospira are long slender spiral-shaped bacteria, found in most mammalian host species. Over 160 serotypes are known, generally called serovars, with cross infections occurring between some host species. Each serotype has one or more (usually only two or three) reservoir hosts which multiply it up and maintain it. A serotype can remain as a life-long infection in its reservoir host.
The pig is a reservoir host for Leptospira pomona, L. tarassovi, L. bratislava and L. muenchen, the last two being very closely related. It is not a reservoir host for L. icterohaemorrhagiae but it can be infected from rats urine and become ill. It can also become infected by other serotypes from other animals urine, for example L. canicola from dogs and L. hardjo from cattle but the infections are subclinical and do not result in disease. The pig is then an incidental host i.e. does not perpetuate the infection and is only responsible for minimal spread.
L. pomona causes important reproductive problems in female breeding pigs spreading slowly through the herd. It remains in the herd permanently unless steps are taken to eradicate it. It is not in the UK or Ireland and seems to have disappeared from Western Europe but is widespread throughout the rest of the pig rearing world. In America the skunk is an alternative reservoir host.
L. tarassovi causes a similar syndrome (i.e. a collection of signs and lesions) to L. pomona but tends to be milder and to spread more slowly. It is found in Eastern Europe and the Antipodes. It is thought that some wild animals are also reservoir hosts.
The pig is also a reservoir host for certain subtypes of L. bratislava and L. muenchen which are widespread throughout the pigs of the world. They cause a different syndrome to L. pomona and L. tarassovi and affect mainly pregnant gilts and second litter females because they will not previously have encountered it.
Once these organisms are introduced into a herd the pigs become permanent carriers with infection of the kidneys and intermittent excretion of the organism into the urine. L. bratislava/muenchen also permanently inhabit the fallopian tube of sows and the reproductive organs of boars and they are spread in semen.
Disease is uncommon in the sucking pig and would only infect individuals.
Growing pigs are occasionally exposed to Leptospira icterohaemorrhagiae from the urine of rats.
Remember that this disease can be transmitted to people.
Symptoms
Piglets
- Uncommon.
- Illness.
- Inappetence.
- Jaundice.
- Blood in urine.
- Severely infected pigs die.
Sows In acute outbreaks:
- Inappetence.
- Fever.
- Depression may be observed.
Chronic low grade disease is more common with:
- Abortions.
- Stillbirths.
- Increase in poor, non-viable pigs.
If abortions in a herd are more than 1% then investigations for leptospirosis should be considered. A reduction in farrowing rates and numbers of live pigs born per sow is also an associated factor particularly with L. bratislava infection.
Signs associated with acute L. bratislava disease:
- Repeat breeders are common particularly in first and to some extent second pregnancy gilts.
- This often follows embryo loss and there may be copious vaginal discharges.
- Late term abortions.
- An increase in premature piglets.
- An increase in stillbirths.
- Mixed litters of live poor pigs and dead piglets at birth.
- An increase in mummified pigs.
- An increase in repeat breeding animals.
- Often there is a two year cycle of disease.
- Reproductive failure occurs in second litter females, rather than gilts following their introduction to older carrier boars.
- Disease is less common in older animals.
- In long standing carrier herds disease can be difficult to recognise.
Weaners & Growers
- Acute jaundice.
- Haemorrhage.
- Rapid death.
- Pale pigs.
Causes / Contributing factors
- Introduction of infected gilts and boars.
- The presence of PRRS in the herd.
- AI
- Infection brought into the herd by other animals; rats, mice and dogs can be reservoirs of infection.
- Exposure of the herd to indirect sources of contamination, e.g.: contaminated water, poor floor surfaces allow urine to pool. Spread in urine.
Diagnosis
This is difficult but the following will help:
- Records. Study the levels of abortions, repeats, stillbirths, week piglets and the age of occurrence in sows and gilts.
- Study the clinical picture.
- Blood sample suspicious animals and repeat 2-3 weeks later. Look for rising antibody titres e.g. 1st sample result 1:100, 2nd result 1:800. This would confirm active infection and indicate probable involvement.
- Blood sample ten females that have a history of infertility.
- In chronic disease however, the significance of titre levels are very difficult to assess.
- Test the aborted foetuses, urine or kidneys and fallopian tubes of slaughtered gilts.
- Eliminate other diseases – Chronic PRRS, endometritis.
- Eliminate non infectious causes of infertility – Summer infertility, management failures.
- The symptoms of leptospirosis can be mistaken for other causes of infertility.