There are three species of hookworms that afflict dogs. These parasites are most prevalent in areas of high temperature and humidity (such as the southern United States), where conditions are favorable for the rapid development and spread of larvae.
Hookworms are small, thin worms about one-quarter to one-half inch (.6 to 1.3 cm) long. They fasten their mouth parts onto the mucosa of the small intestines and suck blood and tissue fluids from the host. This can result in severe blood loss and malnutrition.
There are five routes by which puppies (and adult dogs) can acquire the infection:
Migration through the placenta in utero
Ingesting larvae in mother’s milk
Ingesting larvae in the soil
Direct penetration of the skin (usually through the pads of the feet)
Ingesting an intermediate host
The majority of serious hookworm infestations in puppies occur during the first two months of life and are acquired through the mother’s milk. Signs of illness include bloody, wine-dark, or tar-black diarrhea. Progressive blood loss may cause these puppies to rapidly sicken and die. Intensive veterinary management is required.
In adult dogs, the most common routes of infection are ingesting larvae and larvae migrating through the skin. Some larvae encyst in tissues, while others migrate through the lungs to the intestines, where they mature into adults. In two to three weeks the dog begins to pass eggs in her feces. These eggs incubate in the soil. Under proper conditions, the eggs hatch in 48 hours and release larvae that are infective in five to seven days.
Dogs with chronic hookworms often have no symptoms. When symptoms do occur, they include tarry or bloody diarrhea, pale mucous membranes caused by anemia, weight loss and emaciation, and progressive weakness. Symptoms can appear as early as 10 days after exposure. The diagnosis is made by finding eggs in the feces. Because eggs do not appear in the feces for two to three weeks, however, there may be an interval during which a stool examination is negative and the diagnosis must be made on the basis of clinical signs.