Leptospira are fine spiral bacteria (spirochaetes). They can be grown in the laboratory but required complex media and primary isolation takes 2-6 weeks. The 9 species are divided into serogroups, serovars and subdivisions which cause particular syndromes. L. interrogans serogroup Australis serovar bratislava genotype B2b and serovar muenchen M2 cause abortion and serovar bratislava B2a causes meningitis. Leptospirae are sensitive to antimicrobials such as penicillin and streptomycin, to most disinfectants, to soaps and are rapidly destroyed by drying. The persist for weeks in water. Serogroups Pomona, Canicola, Tarassovi, Ictero-haemorrhagiae, Sejroe and Australis all occur in pigs The organisms cause septicaemia, damage the liver and penetrate the kidney tubules. Leptospirae are shed in the urine. They infect the fallopian tubes and seminal vesicles and enter the pregnant uterus, invade foetuses and cause abortion 10 days to 4 weeks after infection. L. muenchen causes few clinical signs in sows and a short period of leptospiruria (30 days). Leptospirae enter the genital tract from systemic infection or from venereal infection. Embryos and foetuses must be infected prior to 50 days of gestation for death to result.
Leptospirae are shed in the urine of carrier animals. When the pig is the carrier, as with some members of the L. interrogans Pomona and Australis serogroups, then pig urine is generally the source of infection. When it is the rat as in L.interrogans Icterohaemorrhagiae, it is rat urine. Infection from urine by ingestion, direct contact, through abrasions either by direct transmission or by contact with infected water. Transplacental transmission is possible as the organisms colonise the developing foetus and organisms infect the male genital tract resulting in venereal transmission Infection with serogroups other than those adapted to the pig are normally spread to pigs by contact with their urine or by contaminated water. This environmental transmission can occur anywhere, but the pig-adapted strains are, in most cases, introduced to clean farms by carrier pigs.
Infection may be inapparent especially in finishing pigs and gilts reared extensively in which clinical signs of disease are rarely seen. Fever to 40°C (105.8°F) for 35 days may occur in Canicola Icterohaemorrhagiae, Pomona and Tarassovi infections. Affected pigs become dull, anorexic, show diarrhoea and rarely develop jaundice with or without haemoglobinuria (red coloured urine). Heavy mortality may occur, particularly in piglets. Nervous signs may be seen, e.g. weakness of the hindquarters, meningitis or tremor if leptospirae enter nervous tissue. Animals with severe jaundice, haemorrhagic disease or nervous signs may die. Abortion, stillbirth and neonatal mortality accompanied by fever, loss of milk and jaundice in the sows are common consequences of leptospiral infection in breeding herds. Australis serovars muenchen and bratislava and serogroups Canicola and Pomona can all be involved. Abortion may occur 47 days after infection in sows less than 45 weeks pregnant. In sows which are infected later, weak piglets may be born. Mummified and macerated foetuses occur commonly amongst the litters of sows with leptospirosis. Abortion in the last trimester (third) of pregnancy is common. Infertility associated with venereal spread in non-immune herds may be responsible for returns to service, particularly with the Australis serovars bratislava and muenchen.
Abortion in the last third of pregnancy, reduced conception rate, vulval discharge, the birth of weak piglets, and fever with icterus and mortality in older piglets and weaners may suggest leptospirosis. Diagnosis is confirmed by demonstration of the organism in fresh urine, semen, aborted foetuses and slaughtered pigs by culture. It may also be demonstrated in tussle by immunofluorescence or immunoperoxidase, and by DNA probes. Antibodies to leptospira appear in the serum with 1-2 weeks or infection and reach high levels which may persist for some weeks. Serum antibody can only be used as a herd test as infected animals may be seronegative. Antibody in thoracic fluid in stillborn foetuses confirms infections.
Post-mortem findings of greyish white kidney lesions, 1-3 mm in diameter, sometimes with a red ring occur in the cortex. Petechiation (blood spots) may be present. Septicaemic changes, jaundice and liver damage occur in acute cases. Aborted foetuses may be mummified, or have uniformly pale organs with or without jaundice. Freshly aborted foetuses often have petechiae on the skin and haemorrhages in kidney, lungs and liver. Straw coloured fluid is present in body cavities. Mummification is uncommon in Australis infection and abortion occurs in the last third of gestation or piglets are stillborn.
Leptospirosis can be treated by injection with penicillin, semisynthetic penicillins, and streptomycin in acutely ill animals. Abortions may be prevented and renal carriers eliminated by injection with streptomycin (25 mg/kg) as a single dose or for 3-5 days. Treatment 1 week before service and 2 weeks before farrowing has been found to be most satisfactory in preventing reproductive losses. Feed or water medication with tetracyclines at 800 g/tonne may be of value. Re-infection should be prevented by hygiene and isolation. Vaccination of uninfected sows before service with killed vaccines containing the appropriate serotype or serotypes may prevent abortion. Piglets should be vaccinated before the period of risk (6-10 weeks of age), but if protection does not result, confirm the point at which infection is occurring by preparing a herd serum antibody profile and vaccinate prior to exposure. Vaccination may not prevent renal colonisation and is unlikely to eliminate it if it is already established. Regular revaccination is advisable. Transmission of infection may be eliminated by hygiene, vaccination, treatment or slaughter of carriers or a total slaughter policy combined with disinfection, elimination of rodents and restocking. Leptospira in pig urine or infected foetesus can infect man and hygiene is advisable. The use of artificial insemination using diluents containing antimicrobial can reduce or eliminate venereal transmission.
Leptospirae can infect humans after contact with contaminated pig urine or the products of abortion. As soaps, most disinfectants and drying eliminate leptospirae, simple hygiene can protect workers at risk from this infection.