Hookworms are common intestinal parasites found in many different species of animals. Puppies are commonly infected by hookworms while nursing, which can quickly lead to severe anemia. Dogs of any age can become infected with hookworms from environmental exposure or predation. 

Once infected, hookworms attach themselves to the wall of the small intestines with their sharp, hook-like mouths, causing damage and sucking blood. The hookworms can detach and reattach to a new spot on the intestines, leaving small bleeding ulcers behind. Hookworm exposure in people can cause skin infections called cutaneous larval migrans. Year-round broad-spectrum parasite prevention and environmental management are essential to prevent exposure to pets and people. 

Cause

Hookworms are very small nematode parasites of several species, including A. caninum, A. braziliens, and U. stenocephala. Dogs can become infected after ingesting mature larvae in a feces-contaminated environment or ingestion of prey, like rodents, with larvae in their tissues. Once the larvae are ingested, they mature into adults in the gastrointestinal (GI)  tract, or they can penetrate the oral mucosa and migrate through the bloodstream to the lungs. Once in the lungs, the larvae are coughed up and swallowed into the GI tract. Dogs can also become infected by hookworm larvae that penetrate through the skin and migrate through the bloodstream. Infected dogs defecate hookworm eggs into the environment, which hatch into larvae and then mature through three stages of development over 2-9 days before they are infective to another dog. 

Hookworm larvae can migrate through the body and become dormant in the dog’s tissues. Even if they are on a monthly preventative for dogs, dormant hookworms are not affected. These arrested larvae can become activated during pregnancy and lactation, where the larvae then accumulate in the mammary glands. For this reason, puppies commonly get hookworms from their mothers while nursing, and is why all nursing puppies are assumed to be at risk of hookworm. A. caninum is the most common species in dogs to cause acutely significant anemia and even death in young puppies infected during nursing.

Clinical signs

Most clinical signs of hookworm infections are related to GI distress or anemia. Some dogs do not develop signs of illness, while puppies are much more likely to develop signs of disease. If larvae migrate through the lungs, respiratory signs may occur. Skin signs can occur if larvae migrate through the skin.

• Diarrhea
• Inappetence
• Lethargy
• Melena (digested blood in stool)
• Weakness
• Dehydration
• Pale gums
• Vomiting
• Coughing
• Poor hair coat
• Weight loss
• Failure to thrive
• Red and itchy pimples in between toes

Diagnosis

Hookworms are diagnosed through microscopic identification of hookworm eggs in a sample of feces or through PCR testing of feces. However, because hookworms start sucking blood before any eggs are produced, puppies infected during nursing may suffer from acute anemia before they pass any eggs into their stool.

In cases of severe illness, additional diagnostics may be required, such as blood work to evaluate for anemia.

Treatment

Several anthelmintic medications, such as pyrantel pamoate, kill adult hookworms. This treatment is repeated every 2-3 weeks to kill any new adult hookworms that were larvae during the first round of treatment. Many monthly heartworm preventatives, such as ivermectin/pyrantel or milbemycin oxime, kill the larval stages of hookworms to help prevent re-infection. These medications do not kill the arrested larvae, which can exist in the body's tissues.

After hookworm treatment, the parasite detaches from the intestine. It leaves an ulcerative lesion that can continue bleeding for a few days, which is why some anemia will worsen after receiving treatment medications. Severely affected animals may require more intensive treatment, including medications to protect the gastrointestinal tract, such as sucralfate, fluid therapy, and, in some cases, blood transfusions. 

Outcome

Most dogs with hookworms respond well to treatment. Reinfection may be common without proper environmental management. Puppies that experience severe illness from hookworms may be more likely to have serious complications and, in rare cases, even death. Your veterinarian may repeat a fecal exam or recheck blood work to monitor anemia. 

Prevention

• Prompt feces removal is recommended to prevent contamination with hookworm eggs and larvae, which are hardy in the environment. 
• Prevent predation or scavenging of prey animals.
• Keep dogs on monthly parasite preventatives.
• Deworm pregnant and nursing dogs at regular intervals.
  • Puppies should be treated starting at two weeks of age, then every two weeks until around eight weeks, even if fecal tests are negative, and then started on monthly preventative. 

Zoonosis

Several hookworm species can infect dogs and cats, which can cause infections in people called cutaneous larva migrans (CLM), most commonly from A. braziliense. Infections are more common in children with bare feet if their skin contacts larvae in a feces-contaminated environment such as soil or sand in yards, parks, or other public areas. The larvae can migrate in the skin, causing red and itchy lesions. Rarely, humans can also develop an intestinal infection from hookworm larvae, causing severe abdominal pain.

The following measures can prevent zoonotic infection:

• Good hygiene 
• Avoid allowing children to play in potentially contaminated environments
• Prompt removal of feces where pets defecate, especially in public areas
• Cover children’s sandboxes when not in use
• Wear shoes and gloves while gardening 
• Keep pets on monthly parasite preventatives

 July 2024