Dogs and Livestock: The Problem of Parasites

Dogs have been part of the agricultural community for thousands of years. While the exact date of domestication is under a lot of academic debate, common consensus states that dogs have been our companions for at least 20,000 years. From herding livestock to guarding flocks, dogs are still vital members of agricultural communities. On the other hand, having dogs around increases the risk of some parasite infections. So what are the main parasites that dogs can carry and how are these risks managed?

The role of guardian dogs is to protect livestock from predators such as wolves.
The role of guardian dogs is to protect livestock from predators such as wolves. Protozoan Parasites in Dogs and Livestock

Protozoa are single-celled organisms that can be either free-living or parasitic. In dogs, most protozoan infections are localised in the gastrointestinal system, and can cause a wide range of different symptoms. While there are many protozoa which infect dogs, there are relatively few which are zoonotic and can infect other species.

buy Lyrica tablets uk Neosporosis

The Neospora canium parasite causes neosporosis and it is responsible for a significant proportion of cattle abortions in the UK. The parasite’s definitive host is the dog, where the parasite reaches maturity and reproduces. Infected adult dogs rarely show symptoms, but infection can be fatal for puppies and young dogs.

Once the parasite reaches maturity, it will lay oocysts inside the dog. The dog will then excrete these in its faeces. From there, the intermediate hosts ingest the oocysts – these are usually livestock such as cows and sheep. This can happen when livestock graze on contaminated pasture.

Inside the intermediate host, the parasites form cysts. Although the adult intermediate host does not tend to show symptoms, the parasite can damage any developing foetuses. Inside a pregnant animal, the parasite can cross the placenta from the mother to the offspring. Foetuses might abort, or occasionally can be born with brain damage. Parasites are then expelled in the placenta when the mother gives birth. If a dog eats this infected tissue, they can become infected and the cycle starts again.

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Herding dogs help to manage large groups of animals.
Herding dogs help to manage large groups of animals.

Another protozoan disease, sarcocystosis predominantly affects dogs and sheep in the UK. It is extremely common in sheep flocks across the world, but can also infect other animals and people. Sarcocystis is a highly diverse genus, with over 250 different species described. Many species-specific life cycles occur between particular hosts and include a large variety of animals.

Much like Neospora, in the UK, the parasite passes from dogs to sheep through contamination of feed or water by infected faeces. One inside the sheep, it causes muscle cysts. It then transmits back to the definitive dog host through consumption.

Symptoms of infection in both dogs and sheep tend to be very mild. In some extreme cases, sheep can die or might spontaneously abort their lambs, although this is rare. However, the muscle cysts which the parasite forms can cause meat from infected animals to be condemned. Infections can also reduce growth rates in lambs. As such, this disease causes financial losses to producers.

conjunctly Tapeworms

There are four species of tapeworm which have sheep as an intermediate host, and dogs as the definitive host. This means that when sheep consume the parasite through infected pasture, the larval worms form cysts in their organs. One of these, Taenia ovis, is known as ‘sheep measles’ due to the visible lumps it forms in the meat. These tissues can subsequently act as a source of infection for dogs. If dogs become infected, the worms mature and produce worm eggs which are then shed in faeces.

Taenia ovis, and other species of Taenia tapeworms, cause significant economic loss in the sheep industry. While the parasite tends to be relatively harmless, both to the sheep and to the dog, the cysts created by the larvae are often visible in the meat. As a result, the abattoir might trim the meat, or reject the carcass entirely.

Control of Parasite Transfer from Dogs to Livestock

It can be difficult to prevent contamination from dogs when livestock graze on open areas, or where there are public footpaths.
It can be difficult to prevent contamination from dogs when livestock graze on open areas, or where there are public footpaths.

The best way to completely avoid any transmission of parasites between dogs and livestock would be to prevent any contact between the two. This is rarely practicable, as working dogs are often integral in herd management. Even in situations where working dogs are not present, pet dogs might have access to pasture land. As such, these risks must be managed.

Dogs catch these parasites by eating infected tissue. Preventing dogs from eating any deadstock, afterbirth or aborted animals is paramount. At the same time, if dogs are fed raw meat, it must be from parasite-free sources. This is usually achieved through feeding ‘human-grade’ meat, but if in doubt, meat can be cooked to ensure no parasites are present. Commercial dog foods are also safe, as they undergo extensive processing. Farm dogs should be wormed as needed, and this can be established through advice from a vet.

Livestock catch these parasites from contaminated feed or water. This contamination is usually from dog faeces. It is therefore important to pick up any faeces that dogs might produce. If there are public footpaths through pasture, signs directing people to take away their dogs’ waste can be useful.

As with any two-host lifecycle, breaking the cycle can occur at two points. Either the parasite must not enter the definitive host, in this case the dog, or it must not enter the intermediate host, in this case the livestock. The above measures summarise a few of the most common and effective strategies that are in use today.