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Leptospirosis

See also chapter 6.

(544) It can take several forms depending on the serotype or serovars involved. The main serotypes that cause disease in pigs are:

  • Leptospira pomona
  • Leptospira tarassovi
  • Leptospira bratislava/muenchen
  • Leptospira icterohaemorrhagiae
Leptospira hardjo is widespread in the cattle populations of the world and causes bovine abortion. It causes transient infections and antibody responses in pigs but no disease.

L. pomona and L. tarassovi are the only serovars that can be regarded as exotic.

L. pomona infection

The risk to your herd
This is enzootic in many pig rearing parts of the world including North, Central and South America, Australia, New Zealand, South East Asia and Eastern and Central Europe. If you are involved in pig farming in any of these areas it is not an exotic organism and your herd is at risk.

L. pomona is definitely not present in the UK or Ireland and is thought not to be present in other countries of Western Europe with the possible exception of Italy.

So if you are involved in pig farming in Western Europe (except Italy) you can regard it as an exotic organism. The risk to your herd is probably negligible.

If you are involved in exporting pigs from countries of Western Europe, the pigs for export will probably have to be blood-tested for antibodies to L. pomona. You will probably be frustrated to find that a small number will be positive. This is because they have encountered the mosdok serovar, which is present in some species of wildlife, which sometimes cross-infects pigs causing little or no clinical disease. This is so closely related to L. pomona of pigs that it stimulates a positive immune response. It never develops into a herd problem. The pig can be thought of as an end host.

Importance of L. pomona

  • Once it establishes itself in a herd it is difficult to eliminate.
  • It causes reproductive failure with consequent loss in production and income.
  • It also infects people with a disease sometimes called "swine herds' disease", a severe flu-like condition sometimes with meningitis. There is another disease in the human called Weil's disease and this is caused by L. icterohaemorrhagiae.
  • If you are involved in the supply of breeding stock from a farm that has just become infected you would be wise to stop sales.
  • If you are involved in the export of breeding stock the importing country will usually require you to either test serologically for L. pomona or to put all the pigs for export on a course of streptomycin to eliminate the carrier state. The problem with the former is that some other leptospira serovars that circulate in rodents and hedge-hogs can cross-infect pigs causing no disease but causing cross reactions with L. pomona and false positive results. The problem with the latter is that in some countries (e.g. the USA) streptomycin is not allowed to be used in pigs.
Clinical signs

The disease spreads slowly through the herd causing infertility, abortions and the birth of weak premature piglets. The sows which abort are not otherwise clinically ill. If pregnant cattle are in close contact with the pigs, some of them may also abort.

If any of the pig workers on the farm go down with flu-like symptoms and develop a bad headache call the doctor immediately. Fortunately the disease in people responds to antibiotics if caught soon enough.

Diagnosis

This requires the help of a diagnostic laboratory. Send paired blood samples (i.e. sows sampled on the day they abort and two weeks later) and freshly aborted piglets. The piglets may yield a rapid diagnosis if certain tests are done. Serology on the paired samples inevitably results in at least a two week delay.

The laboratory is likely to carry out micro-agglutination/lysis tests to demonstrate rising antibody titres in the sows and the presence of antibodies in the piglets' serum. The latter is conclusively diagnostic. The laboratory may also try to demonstrate the leptospiras in aborted piglets' tissues using fluorescent antibody tests (FATs) and sections stained with aniline dyes.

Management control and prevention

  • Vaccination - Routine vaccination of breeding stock is practised commonly in countries in which the organism is enzootic but not so much in fringe and free areas. The vaccine, like all bacterial vaccines (bacterins) does not provide a solid immunity but usually raises the resistance sufficiently to prevent clinical signs. Vaccines used are inactivated and contain an adjuvant.
  • Take care in the sources of your replacement stock to ensure that they are not carrying the organism.
  • The organism is spread in urine from carrier animals. It can live fairly long periods in water contaminated by infected urine. Do not provide water from questionable streams and keep your water supplies and tanks clean and free from contamination.
  • Contamination from pig lorries are a minor risk as compared to other infections unless the lorry has other pigs present.
  • Also read the last section of this chapter.
L. tarassovi

This appears to be a pig adapted strain that causes reproductive problems similar to but milder than L. pomona.

There are very few recent reports of this in pigs. It seemed to be confined to Central and Eastern Europe, Australia and New Zealand and presumably is still there. It is believed to be still present in Hungary and Western Russia so if you live in these countries your pigs may be at risk.

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