Humans usually become infected via direct or indirect contact with urine from infected animals. The bacteria enter the body via the eyes, nose, mouth or abrased skin.
Types of Leptospira
Two different Leptospira species (L. borgpetersenii and L. interrogans) and a number of strains (serovars) of each of the species have been isolated from NZ animals.
Species of Leptospira
Likely Primary (reservoir) hosts
Likely Primary (reservoir) hosts
In New Zealand serovars Ballum, Hardjobovis and Pomona are currently those most commonly identified with disease in humans, whilst Hardjobovis, Pomona and Copenhageni are most likely to cause disease in livestock.
Dogs and cats can also become infected with Leptospira and may pose a risk to their owners.
Recently cases of Tarassovi have been diagnosed in people, and cattle have been infected with this serovar. Tarassovi is usually associated with pigs and rodents, and increasing rates of infection in people and cattle may reflect changes in farm practices, such as more storage of supplementary feed on farm, that encourage rodents.
What are the signs in animals?
The signs seen in animals will depend on whether the animals are primary (reservoir) hosts or secondary hosts. Some strains of Leptospira are adapted to certain mammalian hosts and these are referred to as primary hosts.
These primary hosts intermittently, but consistently, shed infectious bacteria via their urine into the environment, and generally show only minor clinical signs. In these hosts the Leptospira bacteria remain in the kidneys for long periods of time – at least 18 months and perhaps for years.
Cattle and sheep are primary hosts for Hardjobovis (and sometimes Pomona) and clinical signs after infection are uncommon, however the animals will be shedding bacteria in their urine.
Cattle, sheep and deer are secondary hosts for Copenhageni (and sometimes Pomona). Infection with these strains will cause more severe clinical signs. In cows these can include mastitis, a drop in milk production, and abortion. In calves the signs include depression, high fever, jaundice (yellow mucous membranes) and red water (blood in the urine), with deaths commonly occurring. Deaths of lambs and abortions in ewes and deer can be caused by these strains.
How is it spread?
Livestock become infected by contact with water or grazing pasture contaminated by urine from infected animals or through mating. Leptospira can survive for extended periods of time in damp soil and stagnant water, and can spread rapidly after heavy rain or flooding.
The bacteria are extremely infectious and can penetrate intact mucous membranes, and skin that has been softened by exposure to water. Cuts and abrasions make it easier for the bacteria to enter the body.
However, the bacteria do not survive well out of water so there is little infection risk from dry surfaces.
How common is it?
Leptospirosis occurs in all livestock species in New Zealand. A recent study conducted by Massey University showed that around 27% of dairy farms have animals shedding Leptospira bacteria and on these farms around 9% of the cows were shedders.
Of the five serovars tested, only Tarassovi was associated with shedding. Rates of shedding are higher on unvaccinated sheep, beef and deer farms.
Rates of leptospirosis in people in New Zealand are high by international standards. In 2015 there were 63 notified cases, 44 of whom were hospitalized. Farmers and farm workers accounted for 36 of these cases. Results from blood tests of people at risk show that there are about 40-50 people infected each year for every one confirmed case.
Leptospirosis in people
Humans usually become infected via direct or indirect contact with urine from infected animals. This can include contact with urine contaminated water e.g. puddles. The bacteria invade either through the body’s mucous membranes (eyes, nose and mouth) or through cuts and abrasions.
Aborted material or assisting a cow with calving can also cause infection as well as contact with urine or kidneys from home-kill or when hunting (pigs and deer) or when dealing with rodents/possums.
In people it can cause a minor flu-like sickness, but may also make some people seriously ill, needing intensive care at hospital. They may be off work for several months, have lasting kidney or liver damage, and may suffer long term fatigue and depression.
Traditionally the disease has mostly been occupationally-acquired with strong links to the meat processing, farming and forestry industries. Overseas, leptospirosis has also been linked with outdoor recreational pursuits and flooding events.
Infection can only be limited by preventing exposure to the bacteria. A key part of this is minimising the number of bacteria shed by animals to reduce the environmental contamination. This can be done very effectively with herd vaccination programmes.
However, it is important to note that not all of the serovars of lepto that might be shed by cattle are prevented by the current vaccines, so minimising contact with urine is important even in vaccinated herds.
It is also important that all people working with animals are aware of the risks and know what to do before entering areas where they are exposed to animals, or animal urine. Preventative measures for people include practicing good personal hygiene – this includes washing and drying hands prior to eating, and not eating, drinking or smoking in the cow shed. Everyone should wear and use the appropriate protective clothing and equipment, and seek medical help early if feeling unwell, especially if flu-like signs are present. Immediate diagnosis and treatment can prevent long-term health effects.
For more information see Leptospirosis: working with dairy cattle.
The dynamics of leptospirosis on farm are complex, however control is possible with an effective animal vaccination programme and a focus on minimising hazards.
Herd vaccination programmes need to include all classes of stock on farm, this includes cows, calves, heifers, carryover cows, bulls, beef cattle etc. Calves should receive an initial and booster vaccination before they pick up infection, and all other animals should be on an annual vaccination schedule. Your veterinarian will be able to advise you on the right approach for your herd.
All current vaccines are very effective in controlling leptospirosis caused by the serovars included in the vaccine, if started at the right age and given to all stock annually.
In addition, minimising hazards such as reducing stock access to stagnant water, controlling rodents and other wildlife, and general hygiene will help reduce the risk of transmission and infection.
Other species on farm such as deer, sheep, goats and pigs need to be vaccinated as they contribute to the cycling of disease. Keeping pigs on a dairy farm is a high risk for infection in both cattle and people. Pigs and their effluent should not come in contact with cattle and any pigs on the farm need to be included in the farm vaccination programme.