Otherwise known as Nematodes, roundworms are a group of worms which can vary considerably in their life cycle, how they infect the host (the dog in this article) and where they live. Many of the more common species live in the intestines, but others can live in the airways and even inside the heart and blood vessels. The article will concentrate mostly on the common varieties – those with a public health aspect and those with a life threatening potential.
Toxocara Canis and Toxocara Cati are respective dog and cat roundworms of a group of Nematodes called Ascarids. Also in this group is a little-publicised worm called Toxascaris Leonina. Depending on which learned authority you speak to there is great debate about which and how severely these worms may infect humans (a zoonosis). Some authorities believe that it is only Toxocara Canis that is zoonotic, others believe all three types have this potential. The next problem is how serious are they as a human disease? They have been implicated in causing tumours of the eye, leading to blindness and epilepsy, especially in children. It has been quoted that there are two cases per million of the population of the UK that become affected to a clinical level. This is due to migrating larvae ending in the eye or nervous tissue and generating an abnormal tissue response leading to disease. Each of these worms has a different lifecycle, but there are distinct similarities between them. Toxocara Canis affects a high percentage of pups (figures range from 20 to 94%) who obtain the infestation by a number of routes.
The egg changes through larval types in the pup which migrate through the puppies tissues including the liver and lungs before returning to the intestines to become an adult worm which can be up to 18cm long and produce eggs after four weeks. The movement of the larvae through the body tissues is known as ‘visceral larval migrans’ and can occur if a species other than a dog accidentally eats worm eggs (children suck dirty fingers). The larvae occasionally fail to follow their ordained route and can end up in the brain, spinal cord and eye tissues of humans and other species as well. There is an enormous debate on whether adult dogs can develop a full cycle of Toxocara activity. The hormonal activity of the adult dog certainly plays a role in inhibiting or promoting the worms. The worm larvae are activated by pregnancy for instance, and many adult animals may not provide an environment in which the worm can flourish. However, our advice is to worm your dog regularly as the public health risks, and the responsibility of dog ownership demand it.
Puppies show signs of worm infestation in many ways. From a few weeks of age coughing, pneumonia and failing to gain weight may occur. This can develop a pot belly and diarrhoea with increasing weakness, vomiting, emaciation and even death. Puppies and sometimes older dogs may well vomit up large quantities of worms which owners occasionally mistake for elastic bands as they are often coiled. The worms themselves are usually a buff colour.
There are many products which will adequately treat roundworms. The secret to success is to limit the problem as far as is possible; feed cooked meat to your pets, regularly worm all dogs from puppyhood. Worm pregnant bitches with appropriate products; worm at the appropriate intervals as recommended by the manufacturer. Maintain good hygiene such as clearing up dog faeces from gardens and disposing of safely, restrict dogs on beds and chairs, do not share food plates, wash hands after handling. There are many products that are very effective. It is of particular importance to worm the pregnant bitch.
Ancylostoma Caninum is the most important hookworm of dogs. This hookworm is widely distributed and has several interesting aspects to its life cycle. The eggs hatch into larvae on the ground and have the ability to penetrate the skin on contact. Dogs in kenneled environments often develop painful sores around their pads from these migrating larvae. The larvae on entry into the dog may migrate to the small intestine via the lungs damaging the lining and blood vessels of the organ or lie in a quiescent phase in the body tissues. With pregnancy, these larvae may infect the pups prenatally and also through the milk. These are voracious parasites with the potential to cause severe debility due to diarrhoea and blood loss. Faeces may be tar like or with frank blood and can, as suggested, severely affect puppies. The range of symptoms can be great from mild diarrhoea through to emaciation, blood loss, diarrhoea, dehydration and sometimes death.
We would recommend the use of several licensed products are best purchased through your veterinary surgeon who can also give you advice on parasite control. Uncinaria Stenocephala is another hookworm, often found in kenneled dogs and has a similar migratory pattern but does not have the same aggressive action in the intestines and so causes far fewer disease problems.
Until recently, Heartworm caused by Dirofilaria Immitis has not been a problem in the United Kingdom. However, two factors are changing this situation, and we should all be warned about the possibilities of this deadly parasite, especially if we live or travel in mainland Europe or live in southern Britain. This is a parasite which relies on its transmission by mosquitoes. The types of mosquitoes carrying the disease are rife in southern Europe including the southern, south-west coast of France, Spain and Italy. With global warming, there is a suggestion that these mosquitoes could live and breed in southern England. There have been cases of heartworm in southern Britain. With the Pet Travel Scheme being operated by the British Government now in place for a few years, we foresee animals returning with this disease from their holidays. When a mosquito bites an infected dog, it collects in the blood the larval form known as microfilaria. The next dog it bites receives some of these microfilariae. The microfilariae migrate through the tissues and six months later develop into adult heartworm which tends to live in the small pulmonary arteries (arteries leading to the lungs directly from the heart). These worms severely damage the arteries causing increased blood pressure in the lungs and inflammatory changes. If there is any possibility of infection, your veterinarian will need to perform immunodiagnostic blood tests, chest x-rays, cardiac ultrasound and blood pressure monitoring.
Coughing, exercise intolerance and difficulty breathing are all seen. This can lead to heart failure. Treatment will kill the heartworms, which once dead, become shed into the lung structure causing a severe pneumonic type reaction. Symptoms are often a lot worse after treatment and blood may be coughed up.
If travelling in Europe, we would recommend preventative therapy with a product containing the drug selamectin. This is applied to the nape of the neck once per month and should kill the microfilariae, so preventing the development of adult heartworm. We would recommend that you consult your vet for treatment for clinical, adult heartworm infections.
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