Leptospirosis in animals – symptoms and outcomes

Leptospirosis in animals – symptoms and outcomes

Technically animals cannot show ‘symptoms’, only signs. Symptoms are those effects of an illness the patient can describe, and headaches are not easy to discuss with a cow.

The disease in animals is almost identical to that in humans, so the signs are also similar. The way the signs display depend on the species and the shape of the animal, and in some they are so characteristic the infection can be diagnosed on sight – in other species the infection will need laboratory tests to detect. This page discusses the infection in layman’s terms suitable for animal owners.

In all animals, age is very important. Young animals just being weaned have a weakened immune system and are very susceptible to leptospirosis, which will usually cause severe or fatal illness. This is very important for breeders and farmers as the optimal age for farming or pet sales is at this point in the life cycle, where animals will be transported and mixed, leading to exposure and a high risk of infection. In adult life animals have better immune systems, and some are entirely immune (such as birds). Illness in adult animals can still happen, but the outcomes are usually better.

Pregnant animals are another area of great importance, as the fetus can be infected across the placenta. In many animals this results in stillbirth or a baby with critical damage to internal organs at birth. If the baby survives it can become a long-term carrier of the bacteria and so can then shed infectious urine. This is why it is mandatory in many countries for pregnant livestock to be vaccinated after the first trimester – this allows the fetus to develop antibodies and prevents in-utero infection. In areas where this vaccination does not happen (such as the developing world), animal populations can become almost entirely carrier-state positive over a few generations.

The bacteria cause local damage to blood vessels, and so the early results are hemorrhages, kidney damage (nephritis) leading to blood in the urine, plus pain. Given the way most 4-legged animals are built, pain in the kidneys causes the animal to walk with a very characteristic arched back, and this is seen in dogs, farmstock and even in rodents. The animals are often reluctant to move rapidly, and will show a fever. Dogs also usually show blood in the whites of their eyes, making them look pink. In later stages, jaundice can develop leading to bright yellow eyes (and skin, but in most species this is impossible to see).


Domestic dogs are routinely vaccinated, and leptospirosis is therefore variable and rapidly evolving, as serogroups not within the vaccine gain footholds and then vaccines are updated. Dogs can present a direct risk of infection to humans though it is surprisingly rare for pets to infect their owners. Symptoms are general, including fever, vomiting, arched back, refusal to eat, lack of activity and failure of pregnancy. It is important to note that dogs must be regularly revaccinated, and in some cases they can still be carriers of the bacteria. Cases are known where vaccinated dogs showed leptospira in their urine even though they showed no clinical signs.

Cattle (plus deer and related species)

Cattle are the maintentance hosts for hardjo, but as this is specialised to survive within cattle, the infection is less severe. Animals infected with other strains (such as pomona) suffer more severe illness. Within industrial farming it is normal, and often law, to vaccinate cattle against a set of the most common serogroups (in the USA a 5-set vaccine is often used). The infection can be directly fatal to young animals, but is rarely fatal in adults. It usually causes failure of pregnancy in cattle (usually after 5 months), and this is the primary economic (and most common) outcome of a herd being infected. Mastitis and drop in yield is common in dairy herds, and the bacteria can often be isolated from milk (though are inactivated by pasteurisation). Acute infection in calves results in severe symptoms and is usually fatal, though early signs include high fever and bloodstained urine (commonly known as redwater fever). Calves born from vaccinated cows are only immune for about 6 months, and will need their own program of vaccination. As a severe infection is common with pomona, and this is a pig-borne serogroup, it is important to keep unvaccinated cattle and pigs separated.

Pigs (plus related species)

Pig infection is potentially extremely important, although very variable. In some countries such as the UK, infection rates are very low, but in others pigs may be the primary route for human infection. Pigs in the carrier state excrete very large amounts of bacteria compared to other species. Their close proximity to humans in many areas of the world make them very significant hosts. As for cattle, the young and pregnant animals are the main issue, and adult nonpregnant pigs rarely show illness (but they can be carriers). Infant pigs are usually killed, and show jaundice, fever, convulsions, hemorrhagia, bloodstained urine, pink eyes and renal failure. Pregnant sows often show hardly any symptoms but will abort a few weeks after infection, and this can sometimes be the only sign a stock is carrying leptospirosis.

Horses (plus related species)

Horse infection can occur, but is rarer than in other livestock. Symptoms are usually mild and non-specific, so diagnosis is probably often missed and this could be the casue of the very low incidence figures. Again, unborn fetuses may be aborted and newborn foals may show acute illness, sometimes fatal. One strange aspect of horse infection is that several months after the acute infection there can be a secondary eye illness (perhaps in up to 50% of cases) called periodic opthalmia (iridocyclitis) – commonly called ‘moon blindness’. It can spontaneously improve or lead to permanent loss of sight. More information on this condition can be found HERE.
There is currently no vaccine for horses, though they are being developed in the US and elsewhere. Use of cattle vaccines on horses (off-label use) is known to happen but is unsafe and potentially illegal in some countries.

Sheep (plus goats and related species)

Sheep show relatively little incidence of infection, and when they do it behaves as for cattle, with major illness only in young or pregnant animals. Sheep can become transient carriers and present risk to humans, but again cases are quite rare as the animals shed only for a brief period. Direct sheep-sheep transfer is also rare. About 15% to 20% of spontaneous abortions in sheep and goats seem to be resultant from leptospirosis, though this varies dramatically by region. Vaccines are available in many areas but are not used routinely, and usually are only given if a flock shows an outbreak of unexplained abortion.