Hookworms dwell in the small intestine of dogs and cats. They have well developed cutting tooth and are voracious blood suckers. Ancylostoma caninum and Ancylostoma braziliense affect both dogs and cats whereas Ancylostoma tubaeforme affects cats only.
What’s in the name?
The anterior end of the worms is bent dorsally like a hook and hence they are named commonly as ‘hookworms’.
Female hookworms lay about 16,000 eggs per day which are passed in the faeces of dogs and cats depending on the affected animal. In a week’s time, the eggs that are passed out in the faeces develop into infective larvae (normally the third stage larva i.e. L3). The infective larvae (L3) prefer moist conditions and they are found mostly in sandy and damp soil.
Dogs and cats get infected either by ingestion of the infective larvae (L3) orally or by skin penetration by the larvae. Prenatal and transmammary infections (through milk, very common in puppies and kittens) can also occur. The habit of licking the grass by dogs and cats facilitates easy entry of infective larvae orally. Larvae ingested orally either develop directly to adults or migrate through the trachea and reach the small intestine to become adults.
Larvae entering by skin penetration reach the lungs via circulation and then through the trachea, reach the intestine to develop as adult hookworms.
In older female dogs following oral ingestion or skin penetration, a few larvae (L3) directly develop to adult but majority of the larvae migrate to various tissues and remain dormant until pregnancy. In the pregnant animals, such dormant larvae get activated by the hormonal influence and these activated larvae enter the developing foetus via placental circulation. The developing worms do not mature in the foetus until the pups are born. They mature within 25-30 days of birth of pups and kittens and eggs can be seen in the faeces. Prenatal infection (placental transmission) is common in pups only.
The larvae which are passed to pups via colostrum directly develop to adult worms without any migration in the tissues. Paratenic hosts like rodents may also be involved wherein infection is acquired by dogs and cats due to ingestion of infected rodents having the larvae of hookworms.
affect the pet?
Heavy infection is common in young puppies and kittens below six months to one-year-old. Smaller breeds are severely affected than larger breeds. Hookworms are attached to intestinal wall and voraciously suck the blood. The worms have the habit of frequently changing the site of attachment, leading to severe bleeding and bite wounds in the intestine, resembling ulcers. The worms also secrete anticoagulants while blood feeding and this leads to continuous oozing of blood in the intestinal wall. In heavy infections, where the number of hookworms could be in thousands, puppies and kittens become anaemic since each worm can suck about 0.001 ml of blood per day. Due to skin penetration of infective larvae, dermatitis and swelling of subcutaneous tissue can be seen. Owing to continuous blood loss, anaemia occurs and in severe infections death results particularly in young animals.
Anaemia is the striking clinical sign which is evidenced by pale mucous membrane, diarrhoea with bloody mucous and infected animals usually pass tarry red coloured faeces. Edema of legs and dependant parts, dry and harsh skin coat and stunted growth are common clinical signs. Infection is usually diagnosed by clinical signs and faecal examination for hookworm eggs.
Hookworms are also zoonotically important. In human beings, especially children, they cause a condition called Cutaneous Larval Migrans (CLM) or Creeping Eruption which occurs due to the skin penetration of the larvae of hookworms when children play with bare foot in areas inhabited by infected dogs where the soil is fully contaminated with infective hookworm larvae. Infection is featured by inflammatory tracts, oedema, pruritus, erythema, vesicle formation and burning sensation at the site of larval penetration in the skin.
Anthelmintics such as disophenol, mebendazole, tetramisole, levamisole and fenbendazole are found to be effective. Periodic deworming of pups, hygienic maintenance of kennels, treating the floor of kennels with common salt or sodium borate solution, proper disposal of dog faeces and keeping the kennels and surroundings dry can control the infection to a larger extent.