hookworm (zoonotic)

Our pets can be hosts for a wide range of parasites. Some of these parasites are harmless to humans, but others can cause serious illness if we become infected. Many of these infectious parasites are transmitted via the feces of our pet dogs (or cats), making it important to understand how these parasites live, breed, and especially, the best ways to prevent our pet’s environment from becoming infective and causing a health-risk to us. One such parasite is the dog hookworm which can cause severe intestinal problems.

Hookworms are a group of parasitic, nematode worms. Three species of hookworm can infect dogs and humans. These are Ancylostoma caninum, Ancylostoma braziliense and Uncinaria stenocephala.

These parasites are most prevalent in areas of high temperature and humidity, such as the southern United States, where conditions are favorable for them to rapid develop and spread. 

Hookworms are small, thin worms, about ¼ – ½ inch long. As adults, they attach their mouth parts into the lining of the small intestine of your dog, or other host, and suck blood and other tissue fluids. This can result in severe blood loss (anemia) and subsequently, malnutrition.

In the A. caninum hookworm, eggs are excreted by dogs in their feces.  Typically, if they land on warm moist soil, they will hatch within 24 hrs.  The hatched larvae become infective within 4 to 5 days and then migrate from the feces into the surrounding soil.  There are 2 possible routes of infection from there to infect another host.

The first route involves the larvae penetrating the skin, usually at hair follicles or sweat glands, but especially in dogs at the footpads and belly where soil contact is frequent and the skin is thin.  The larvae then migrate through the skin and enter the circulatory system which transports them to the lungs.  The larvae leave the circulatory system at the lungs, move up through the trachea and are then swallowed by the host to eventually arrive in the small intestine.  When they get there, they use their 6 sharp teeth to attach to the lining of the intestine.  They then begin to feed by sucking the host’s blood.  Females are thought to produce approximately 10,000 eggs per day.  The time from infection to shedding eggs is 2 to 3 weeks.  Some of the larvae making this migration get “trapped” in the tissue where they encyst.  These larvae remain dormant, but periodically emerge and continue their migration. 

The second, more common, route to the small intestine is by directly ingesting A. caninum.  In this case, the eggs are swallowed during grooming and ingesting contaminated soil, or eating an infected prey animal such as rodents, birds or invertebrates like cockroaches.  The eggs are moved directly to the small intestine of the host where they hatch, become larvae and develop into adults.  The subsequent life-cycle process is identical in either case. 

Puppies can become infected with hookworms by ingesting the larvae in the milk of their infected mother.  Furthermore, puppies can ingest the eggs or larvae from an infected environment, meaning there is a very strong reason for keeping puppies’ environments clean of feces. 

Dogs with chronic (long-term) hookworms often have no symptoms. If your dog does exhibit symptoms, these may appear as early as 10 days after exposure and could include – 

Your dog’s appearance

• Generally unhealthy/poor growth in puppies
• Poor appetite
• Dull coat
• Pale tissues, especially mucous membranes (most easily seen in the gums, lips, nostrils and tissues around the eyes)
• Coughing (due to larvae in the lungs)
• Vomiting
• Redness/itchiness/bleeding at sites of skin infection

Eliminations

• Dark and tarry stool
• Diarrhea
• Constipation

Most serious hookworm infestations in puppies occur during the first weeks and are acquired through the mother’s milk. In adult dogs, the most common routes of infection are ingesting larvae and larvae migrating through the skin. 

Hookworm eggs are not visible to the naked eye and diagnosis is usually made by a microscopic examination to find eggs in the feces.  However, because eggs do not appear in the feces for 2 to 3 weeks after infection, there may be an interval during which the feces examination is falsely negative.  In these cases, the diagnosis is usually made on the observation of clinical symptoms. 

There are a number of worming treatments available that are effective against hookworm. After the initial treatment, this should be repeated in 1 to 2 weeks because the first worming will activate encysted larvae and cause a fresh growth of adult worms to appear in 10 to 12 days. 

Many dogs who have become infected with hookworms and recovered, become carriers.  The larvae become encysted in the dog’s tissues. During periods of stress or illness, these larvae can be released causing a new outbreak of bloody diarrhea as worms reappear in the intestine.