Vet’s viewpoint on leptospirosis

Q: What factors put my herd at risk of leptospirosis?

The most common route for leptospirosis to enter a herd is through an infected animal – which could be through purchased stock or a bull being hired. There’s an additional risk from grazing with sheep which can excrete the Leptospira hardjo bacteria which are responsible for the disease and a further risk when cattle drink from water courses where infected livestock are kept upstream.

Q: How can I avoid bringing leptospirosis in to my herd?

In an ideal situation you’d have a closed herd with no purchasing or hiring in, no access to potentially infected water courses and no co-grazing with sheep. But you have to deal with what you’ve got, which means minimising risks through better biosecurity and – if there’s still a possibility of your cattle becoming infected – it’s well worth vaccinating against the disease. You can also reduce the risks, for example, by only purchasing vaccinated cattle or buying from herds that are ‘accredited’ or ‘monitored’ as ‘free’ from leptospirosis. However, these herds are only ‘free’ from the disease on the day they were tested and they could have become infected since.

Q: What signs of disease should I look out for in my herd?

This can be difficult as to see an epidemic sweeping through a clean herd is unusual these days. In these circumstances you’d see the dramatic clinical signs of a rapid drop in milk production in individuals soon after infection, followed by an abortion storm a short while later. However, far more likely today is a grumbling endemic infection, the greatest cost of which comes through its effect on herd fertility.

Q: Wouldn’t an infected herd eventually develop a natural immunity to the disease?

A herd will develop some immunity but you have to think about the next generation of youngstock coming in. These animals may not have had exposure to infection, especially if they were reared away from the farm. As they come into the herd, they could be very susceptible to infection and all of the associated losses, so this would not be a policy I’d recommend.

Q: What would happen if an infected herd was left untreated?

Left untreated, there would be a mixture of animals in the herd. Some would have been exposed and have some immunity to infection; some would be infected and be spreading infection through the herd; and some would be naïve and picking up infection. You may see the odd abortion and some cows dropping off milk production alongside generally poor fertility, but perhaps not to the extent it would cause the farmer to pick up the phone to the vet.

The difficulty with leptospirosis is even animals which have overcome the disease may harbour the infection in their kidneys and reproductive tract for months, if not years, after their infection. So, they’ll not only continue to excrete the bacteria in their urine, but placental membranes are also likely to be infected. Through these routes they can pass the disease on to other animals, and also on to humans.

Q: Does this mean every herd should be vaccinated?

You have to undertake a risk assessment on a herd-by-herd basis. This will be based on whether the herd is infected now, and what are its risks of infection in the future.

Where I work in Cumbria, for instance, many herds live cheek by jowl; they share water courses and they often purchase animals. The biosecurity risks for herds such as this are high, and I would usually recommend vaccination.

Q: Is there a definitive test to indicate whether your herd is infected?

The two tests we use are a bulk milk test for a dairy herd or blood tests for beef animals across a sample of the herd. The Leptospira bacteria themselves are not easy to identify, so we look for antibodies to the bacteria which indicate the level of immunity the herd has developed. If there is no immunity then there has been no exposure. And if the immunity is high there’s a strong possibility the disease is going through the herd. But it’s the middle ground that’s more difficult to determine and raises the question of whether the disease is still present, or whether it has been and gone and the immunity is trailing away.

By going on to blood test cohorts of similar aged animals the picture can become clearer, with a positive test only in the older animals suggesting it may have been and gone, and antibodies in the youngstock suggesting the disease is currently, or has recently been present. Alternatively, repeating the bulk milk test a few weeks later may show the levels to be rising in an actively infected herd.

Q: What action should be taken in response to a positive test?

In most situations I’d recommend blanket vaccination across the whole herd, including youngstock, before they are turned out with the bull, and earlier still if the risk is high. Turnout is a time of high risk as the bacteria can survive on grassland for a couple of months if conditions are wet. Dietary changes also potentially compound the problem at the same time, as the pH of urine rises as cattle move from silage to grass, and it’s more likely the bacteria will survive in the less acidic urine.

Q: Is the zoonotic risk to humans a serious one?

Although the number of reported cases of leptospirosis in humans is low, there are probably many more cases that remain unreported. Many people have possibly had the disease with its flu-like symptoms and got over it. But if left untreated, it can develop into meningitis which can be very serious, and even fatal. It’s no surprise to me some vets in New Zealand refuse to go on to unvaccinated herds. The nub of the matter is that if you allow your herd to live with a level of infection, you are exposing the people who work with it, as well as the herd itself, to unnecessary risk.

Q: What precautions should be taken by people working with cattle?

If you are employing staff on the farm you owe a duty of care to these people. You should establish whether your herd has been exposed to leptospirosis and tell any prospective employee. Rubber gloves should be worn for handling aborted foetuses and foetal membranes and staff should avoid being splashed with cow urine – which is clearly very difficult for those standing in the pit of a herringbone parlour. By far the best safeguard is to avoid the disease at all, and if you have any suspicions it’s present, vaccinate the herd.

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