Helminthic diseases of animals


The small intestinal tapeworms of major importance in sheep are Monieziaexpansa, Thysaniezia giardi, and Avitellina centripunctata. Other cestodes, such as Stilesia globipunctata and Thysanosoma actinoides occur less frequently, or only in specific regions. Stilesia hepatica parasitizes the bile ducts of sheep and other ruminants. There are three common species that affect dogs and cats: Dipylidiumcaninum which can infect dogs, cats and people uses the flea larvae as intermediate hosts; Taenia pisiformis which infects dogs uses the rabbit; Taenia taeniaeformis which infects cats uses the rat or mouse. The other most common tapeworms that infect dogs and cats are: Dipylidium caninum, Taenia species, Echinococcus granulosus and E. multiocularis, Diphyllobothrium latum and Spirometra mansonoides.

Echinococcus granulosus, also called the Hydatid worm or Hyper Tape-worm, is a cyclophyllid cestode that parasitizes the small intestine of caniids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes hydatid disease.

In caniids, E. granulosus causes a typical tapeworm infection, and produces eggs that are passed with the dog’s faeces. Intermediate hosts include herbivores such as sheep, deer, moose, kangaroos, and wallabies, and any other organism (including humans) that ingests dog faeces. By an accidental ingestion in humans, oncospheres hatch in the duodenum, penetrate the intestine and are carried via the bloodstream to various organs. Hydatid cysts form in organs like liver (60-70 %), lungs and brain. The metacestode cysts develop over years in most cases and have to be surgically removed after diagnosis.

Taeniasis results from either T. saginata or T. solium and relates to the adult worm in the gut. Light infection may be asymptomatic and heavier infection leads to epigastric pain, diarrhoea and vomiting. Cysticercosis is caused by T. solium by larval cysts that infiltrate the lung, liver, eye or brain. This results in inflammation leading to clinical features such as, blindness, neurology.

Treatment is by administering the drug Niclosamide or praziquantel (single dose). There has been suggestion to use a purgative before and after to improve expulsion of the tapeworm.

Taenia saginata, also known as Taeniarhynchus saginata or the Beef tape worm is a parasite of both cattle and humans that occurs where cattle are raised by infected humans maintaining poor hygiene and where meat is eaten without proper cooking. The disease is relatively common in Africa, some parts of Eastern Europe, the Philippines, Mexico, and Latin America.

Hymenolepis nana causes hymenolepiasis in mammals like rodents and humans and is carried by beetles. H. nana has 3 modes of infection: (1) an indirect 2-host cycle involving rodents as primary definitive hosts and grain beetles, fleas, or other insects that feed on contaminated rodent droppings as intermediate hosts; (2) an oral-anal cycle in which eggs are passed from one human to another or recycle externally in a single host; and (3) internal autoinfection, whereby eggs hatch within the gut.


There are two types of Roundworm in dogs and cats, Toxocara canis and Toxascaris leonine, which affect the intestines and causes a pot-bellied appearance. Hookworms (Ancylostoma caninium) occur in the intestines and can also be transmitted to humans. Hookworm is a small, thin worm that hooks on to the intestinal wall and sucks the blood from its victim, which causes anaemia and perhaps death. Whipworms (Trichuris vulpis) are long, thin worms that live in the dog’s colon and are not visible by the naked eye. They attach themselves to the intestinal walls, causing intestinal bleeding, anaemia, weight loss, flatulence, diarrhoea with blood or mucus in the stool and lack of energy.


Heartworm (Dirofilaria immitis) is spread by mosquitoes, which become infected from biting dogs that carry the disease. These dog worms destroy the muscle and tissue of the heart, which can cause congestive heart failure and result in death. At this advanced stage, your dog would experience pot-belly, coughing, lack of energy and dull coat. Acute heartworm disease in cats can result in shock, vomiting, diarrhoea, fainting, and sudden death. Chronic infection can cause loss of appetite, weight loss, lethargy, exercise intolerance, coughing, and difficulty breathing.

Heartworms go through several life stages before they become adults infecting the heart of the host animal. The microfilariae circulate in the bloodstream of dog for as long as two years, waiting for the next stage in their life cycle in the gut of a blood sucking mosquito. When ingested by a mosquito, the microfilariae undergo a series of moults to the infective third larval stage and then migrate to the salivary glands of the mosquito, where they wait to infect another host through mosquito bite.

The current drug is melarsomine dihydrochloride (Immiticide), which has a greater efficacy and fewer side effects than previously used drug, thiacetarsamidesodium (Caparsolate), which makes it a safer alternative for dogs.


Stomach Worms (Draschia megastoma & Habronema muscae) larvae are ingested by fly maggots in manure. The worms develop inside the maggots. Mature flies then deposit the larvae on the lips, nostrils, wounds and other naturally moist areas of the horse, from where they are swallowed as the horse licks the infested area, or they stay in a wound and create oozing, expanding the sores. Larvae deposited in the eyes can cause conjunctivitis. Larvae that are eaten can cause gastritis and tumour-like growths which may rupture.


Oxyspirura mansoni is a widely distributed spiruroid nematode parasite found under the nictitating membrane in the eye of turkeys, chickens, peafowl, quail, and grouse; larvae develop to the infective stage in cockroaches. Eggs pass down tear ducts, are swallowed and pass out in faeces, hatch after ingestion by cockroach. Larvae become infective for final host in 50 days. After ingestion by the final host larvae pass from crop up oesophagus and through tear ducts to eye. Eggs appear in faeces of final host in 32 days.


There are two liver flukes that commonly infect cattle: Fasciola hepatica and Fasciola magna, the former is the most common liver fluke of cattle. It is greyish-brown, leaf-shaped, flatworms with two suckers at the front end. Thriving in the liver of infected cattle, flukes disrupt the normal liver functions such as synthesizing glucose, secreting bile, and synthesizing and storing vitamin A.

Eggs from the animal may be deposited in water where they hatch into miracidium. If snails are present, the conversion from miracidium to cercaria to metacercaria may occur inside the body of snail. The cysts are formed on vegetation, from where they are ingested by cattle or sheep. The intestinal wall is penetrated, followed by the migration of the parasite to liver where significant damage is caused.

The damage to the liver by flukes can be extensive and diarrhoea, weight loss, and jaundice can be observed. Each fluke can cause the loss of 0.5 ml of blood per day from the liver. A moderate infestation in cattle of 100-200 flukes can lead to blood loss of up to half a litre each week that can cause severe anaemia.