Toxocariosis is a pet disease caused by roundworms, transmissible from contaminated environment to both pooches and humans. Here’s more about this dreaded disease, its control and treatment.
Protect your pet from parasites. Parasites play havoc in the well being of the pet animals, particularly the puppies and kittens. Among the parasites, various helminths (worms) are found to be affecting the dogs and cats, which include Toxocara canis (dog roundworm) and Toxocara cati (feline roundworm), respectively. The eggs of these parasites occur in 2-90 percent of soil samples as reported in various countries. The high ambient temperature and humidity of the tropics leads to the dissemination of infection.
Dogs and other canids are the definitive hosts for Tococara canis (T. canis). Adult worms are usually found in the small intestines and shed large number of unembryonated eggs in the faeces. The eggs become embryonated in the environment. Eggs containing L2 stage larva is infective. When a dog ingests the egg with L2, the larvae hatch in the intestine. In pups less than 4-5 weeks old, the larvae migrates via the blood stream into various organs before reaching the intestine back to develop into adult worms. Adult T. canis has a life span of approximately four months in the intestine and most of the parasites are expelled within six months of infection.
In case of older puppies and adult dogs, on ingestion of the eggs with infective larvae, majority of the larva travel to the muscles, liver, kidneys and other viscera where they become dormant. These larvae can mature
in the dog’s intestine without further migration. Dormant larvae serve as a reservoir of infection in pregnant dogs. They become reactivated during the last quarter of pregnancy (approximately by 45 days of gestation) and many of them enter the uterus or mammary gland by which the developing foetus or newborn puppy gets infected.
Transmission can also occur repeatedly to each subsequent litter, without reinfection of the mother. T. canis transmitted through uterus, enters the foetal liver, migrates through the lungs and develops into adults in approximately three weeks. Most of the larvae ingested through the milk do not migrate in tissues, but complete their development in the intestine. Some female dogs develop patent infections during lactation, either from the movement of hypobiotic larvae to the intestines or by the ingestion of larvae from the faeces of their puppies. These infections disappear spontaneously after 4-10 weeks of whelping. Dogs excrete large number of Toxocara eggs, even a mildly infected dog can shed 10,000 eggs in each gram of faeces. Most soil contamination occurs from puppies between the age of three weeks and three months.
Puppies infected via uterus can develop enteric signs within first 2-3 weeks. Pneumonia and other symptoms of tissue migration can appear within a few days of birth. In dogs, young puppies usually have the most severe signs. The typical signs include poor growth, loss of condition and enlarged abdomen (pot belly). Worms may be passed in the faeces or vomitus. Other signs include diarrhoea, constipation, vomiting, flatulence, cough and nasal discharge. In severe cases puppies may die from obstruction of gall bladder, bile duct or pancreatic duct or rupture of the intestine and peritonitis. The migration of the larvae through the liver and lungs can result in inflammation and dyspnea of varying severity. Affected puppies may die within 2 or 3 days of birth mainly because of pneumonia. Severe infections can also cause ascites, fatty degeneration of liver, secondary bacterial pneumonia and chronic stunting. Myocarditis is a rare complication. In adult dogs, high levels of liver enzymes may be seen during larval migration with ocular signs such as orbital cellulitis and multifocal retinal disease.
The eggs containing second stage larva (L2) is considered as zoonotically important as this is easily transmissible to pet parents. The condition is common in human, particularly children below five years of age, who acquire the infection accidentally by ingestion of infective eggs along with contaminated eatables and water apart from improper hygiene by way of contamination of hands with infected soil containing egg with L2 of Toxocara sp. of dogs and cats. The accidental ingestion of the infective stage, results in release of the L2 larva in the intestine of the affected children, which migrates erratically and reaches organs such as liver, lungs etc resulting in a condition called visceral larval migrans (VLM). Occasionally during migration may also reach the chamber of the eye causing ocular larval migrans (OLM).
Treatment and control
Anthelmintics such as pyrantelpamoate, praziquantel are found to be effective in puppies and kittens. Generally for adult dogs and cats, drugs such as Fenbendazole, Levamisole and Albendazole may be effective. With regard to control, puppies and kittens should be dewormed to eliminate the shedding of eggs. Removal of faeces and thorough cleaning of kennels is important. The kennel should be kept as dry as possible. Contamination in public places can be decreased by restricting uncontrolled dogs and cats particularly in playgrounds and parks. There is no practical method available to remove Toxocara eggs from the soil once contamination has occurred.
Either children or adults, everybody is advised to wash hands after playing with their pet dogs.
(Dr A Sangaran, professor; ST Bino Sundar, assistant professor and BR Latha, professor and head are faculty from the Department of Veterinary Parasitology, Madras Veterinary College, Tamil Nadu Veterinary and Animal Sciences University, Chennai)