Hookworms (Ancylostoma spp, Uncinaria stenocephala) are common infections of dogs and cats, particularly puppies and kittens. Some species are zoonotic. Adult parasites reside in the small intestine and are often subclinical; Ancylostoma caninum infections may cause anemia, weakness, melena, and/or hypoproteinemia. Diagnosis is based on examination of feces for parasite eggs and/or antigen. Multiple anthelmintics are approved with activity against hookworms; however, drug resistance in A caninum is an emerging problem. All dogs and cats should be treated preventively.
Multiple hookworm species infect dogs and cats. A caninum is the principal cause of canine hookworm disease in most tropical and subtropical areas of the world and is considered the most pathogenic of the dog hookworms. Ancylostoma tubaeforme infects cats throughout the world. Ancylostoma braziliense infects dogs and cats and is sparsely distributed from Florida to North Carolina in the US. It is also found throughout Central and South America and Africa.
Ancylostoma ceylanicum infects dogs and cats and is widely distributed throughout Asia and parts of southern Africa. U stenocephala is the principal canine hookworm in cooler regions around the world. Historically, it was the predominant canine hookworm in Canada and northern parts of the US, where it is primarily a fox parasite. However, in recent years A caninum has become more common than U stenocephala in dogs in these regions. U stenocephala also is present in cats.
Adult hookworms reside in the small intestine. A caninum males are ~12 mm long and females ~15 mm; the other species are somewhat smaller.
Courtesy of Dr. Andrew Peregrine.
Thin-walled hookworm eggs in the early cleavage stages (2–8 cells) are first passed in the feces 15–20 days after infection; they complete embryonation and hatch in 24–72 hours on warm, moist soil. For all hookworm species, transmission may result from ingestion of infective larvae from the environment and additionally, in the case of A caninum, via the colostrum or milk of infected bitches. Infections with A caninum, A braziliense, A tubaeforme, or A ceylanicum can also result from larval invasion via the skin; however, this route is of little significance for U stenocephala.
Skin penetration in young pups is followed by migration of the larvae via the blood to the lungs, where they are coughed up and swallowed to mature in the small intestine. However, in animals > 3 months old, A caninum larvae, after migration via the lungs, are arrested in the somatic tissues, eg, muscle, fat, and mucosa of small intestine. These arrested larvae may be activated during pregnancy, then accumulate in the mammary glands. Reactivation of dormant larvae, which may also occur after removal of adult worms from the intestine and for other unknown reasons, results in development of patent infections and is referred to as "larval leak."
With respect to zoonotic potential, infective larvae of canine hookworms in the environment, particularly A braziliense, may migrate under the skin of humans and cause cutaneous larva migrans. A caninum can also occasionally cause patent infections in humans. A ceylanicum is an emerging public health risk in parts of Asia; in addition to development of patent infections, larvae may cause papules at the site of skin penetration.
Clinical Findings of Hookworms in Small Animals
An acute normocytic, normochromic anemia followed by hypochromic, microcytic anemia in young puppies is the characteristic, and often fatal, clinical manifestation of A caninum infection. Surviving puppies develop some immunity and show less-severe clinical signs. Nevertheless, debilitated and malnourished animals may continue to be unthrifty and suffer from chronic anemia. Mature, well-nourished dogs may harbor a few worms without showing clinical signs; they are of primary concern as the direct or indirect source of infection for pups. Diarrhea with dark, tarry feces accompanies severe infections. Anemia, anorexia, emaciation, and weakness develop in chronic disease.
Lesions
Anemia results directly from the bloodsucking and the bleeding ulcerations that occur when A caninum shift feeding sites. The amount of blood loss due to a single worm in 24 hours has been estimated to be up to 0.1 mL. There is no interference with erythropoiesis in uncomplicated hookworm disease. The liver and other organs may appear ischemic, and some fatty infiltration of the liver may occur. Hemorrhagic enteritis with a swollen small intestinal mucosa that shows small red ulcers and attached worms usually occurs in acute, fatal cases. Pneumonia and lung consolidation may result from overwhelming infections in pups.
A braziliense, A tubaeforme, A ceylanicum, and U stenocephala are not avid blood feeders, and anemia rarely develops. However, hypoproteinemia is characteristic, and serum seepage around the site of attachment in the intestine may decrease blood protein by > 10%.
In dogs, dermatitis due to larval invasion of the skin may occur with any of the hookworms; however, it is present most frequently in the interdigital spaces with U stenocephala; skin infections with U stenocephala rarely mature.
Diagnosis of Hookworms in Small Animals
Clinical evaluation
Examination of feces for parasite eggs
Examination of feces for hookworm antigen
Courtesy of Dr. Andrew Peregrine.
Courtesy of Dr. Andrew Peregrine.
Many infections are subclinical; clinical signs occur most commonly in young animals. The characteristic thin-shelled, oval eggs are easily seen on flotation of fresh feces from infected dogs and cats (Ancylostoma spp 52–79 × 28–58 mcm; Uncinaria sp 71–92 × 35–58 mcm). Centrifugal fecal flotation methods maximize diagnostic sensitivity, and PCR assay can be used to identify the parasite species. Acute anemia and death from infections acquired via milk may occur in young pups before eggs are passed in their feces, ie, as early as 1–2 weeks.
At least one commercial diagnostic company offers a hookworm fecal antigen test for dogs and cats that detects antigen produced by Ancylostoma spp and Uncinaria spp.
At postmortem examination, the small intestine should be carefully examined for adult parasites and the burden determined. Morphological criteria should be used to identify the parasite species present.
Treatment and Control of Hookworms in Small Animals
Multiple anthelmintics are available for treatment and prevention
Routine fecal monitoring to evaluate anthelmintic efficacy
Prompt disposal of feces
Multiple anthelmintics are available for treatment and prevention of hookworms in small animals. Among drugs for intestinal helminths in dogs, fenbendazole, moxidectin, and pyrantel are approved for treatment of A caninum and U stenocephala infections. Milbemycin is also approved for treatment of A caninum infections. Nitroscanate is also approved for both hookworms at 50 mg/kg in some countries.1 When anemia is severe, therapy may have to be supported by blood transfusion or supplemental iron, followed by a high-protein diet until the Hgb level is normal.
Bitches should be free of hookworms before breeding and kept out of contaminated areas during pregnancy. Sanitary quarters should be provided for whelping and nursing. Concrete runways that can be washed at least twice a week in warm weather are best. Sunlit clay or sandy runways can be decontaminated with sodium borate (1 kg/2 m2).
Heartworm prevention with products containing milbemycin control A caninum; the combination product milbemycin/afoxolaner (UK) is also approved for control of A braziliense and A ceylanicum. In contrast, ivermectin/pyrantel, ivermectin/pyrantel/praziquantel, moxidectin, and moxidectin/imidacloprid control A caninum and U stenocephala. Heartworm preventives containing pyrantel also have activity against A braziliense ( see Table: Drugs for Intestinal Helminths of Dogs Approved in the US and UK) and are approved for this purpose. Finally, the injectable formulations of moxidectin for heartworm prevention in dogs also have therapeutic efficacy against infection with A caninum and U stenocephala.
For A ceylanicum, the combination product containing pyrantel pamoate/febantel/praziquantel is approved for treatment in Australia; milbemycin/afoxolaner is approved for treatment in the UK.
In cats, drugs approved for treatment of A tubaeforme include emodepside, eprinomectin, fenbendazole, ivermectin, milbemycin, moxidectin, pyrantel, and selamectin ( see Table: Drugs for Intestinal Helminths of Cats Approved in the US and UK). Heartworm prevention with eprinomectin/praziquantel, ivermectin, milbemycin, milbemycin/praziquantel, moxidectin/fluralaner, moxidectin/imidacloprid, selamectin, or selamectin/sarolaner controls A tubaeforme; eprinomectin/praziquantel and ivermectin also control A braziliense ( see Table: Drugs for Intestinal Helminths of Cats Approved in the US and UK). For A ceylanicum in cats, topical selamectin at label dose has been shown to be an effective treatment.
When neonatal pups die due to hookworm infection, subsequent litters from the bitch should be treated weekly for A caninum for ~12 weeks beginning at 2 weeks old. In addition, fenbendazole (25 mg/kg, PO) administered daily to pregnant bitches from day 40 of pregnancy to day 2 after whelping greatly decreases transmammary transmission to the pups (approved in the UK). Likewise, treatment of the bitch with ivermectin (0.5 mg/kg PO) on two occasions (4–9 days before whelping and 10 days later) or with moxidectin/imidacloprid spot-on on day 56 of pregnancy has the same effect (extra-label use).
Resistance of A caninum to pyrantel has been reported in parts of Australia since the 1980s. In 2019, multiple dogs in the southeastern US were described with A caninum infections that were resistant to the three anthelmintic drug classes approved for treatment of hookworms in dogs in the US, ie, benzimidazoles (eg, fenbendazole), macrocyclic lactones (eg, ivermectin, milbemycin), and tetrahydropyrimidines (eg, pyrantel).
Such infections have been detected in multiple dog breeds. However, Greyhounds from Florida are overrepresented. Thus, when treating an A caninum infection, particularly in North America, a fecal examination should be carried out 14 days after treatment to confirm the efficacy of treatment. Dogs with A caninum eggs in feces at that time likely have a drug-resistant infection because larval leak is unlikely to occur until at least 21 days after treatment.
To confirm the resistance, the dog should be retreated with the same drug. A quantitative fecal egg count should be carried out on the day of treatment and 14 days later; drug resistance is likely present if the A caninum fecal egg count drops by less than 75% after treatment. A > 95% reduction in fecal egg count indicates effective treatment, and thus the cause of persistent egg shedding is most likely larval leak.
If drug resistance is confirmed, the dog should be treated using one of the following multianthelmintic drug class combinations with all the drugs administered concurrently at labeled doses:
fenbendazole (50 mg/kg PO once daily for 3 days) + pyrantel pamoate (5 mg/kg PO) + moxidectin (2.5 mg/kg topical)
febantel (25 mg/kg PO)/pyrantel pamoate (5 mg/kg PO)/praziquantel (5 mg/kg PO) + moxidectin (2.5 mg/kg topical)
In cases refractory to this treatment protocol, the following treatments have been shown to be effective:
emodepside/praziquantel (for dogs), PO, at label dose
emodepside/praziquantel (for cats), administered PO, using an emodepside dose of 1 mg/kg (one-third of the topical labeled dose for cats)
nitroscanate, PO, at label dose
Treatments (1) and (3) are not currently approved for use in the US; (2) is only approved for use on cats in the US. When using emodepside, note that dogs with a mutation of the multidrug resistance (MDR1) gene may be at increased risk of adverse effects.
Prevention programs for hookworms, in all ages of dogs and cats, are as recommended for roundworms.
References
Boray PA, Strong MB, Allison JR, Oreilli M von, Sarasin G, Gfeller W. Nitroscanate: a new broad spectrum anthelmintic against nematodes of cats and dogs. Aus Vet J 55(2):45–53.
Key Points
Ancylostoma spp and Uncinaria stenocephala are common infections of dogs and cats, particularly young animals. Infections are acquired via multiple routes.
Adult parasites reside in the small intestine. While infections are often subclinical, clinical signs are most commonly associated with A caninum and include anemia, weakness, and melenic feces.
Diagnosis is based on identification of parasite eggs and/or hookworm antigen in feces.
A braziliense and A ceylanicum constitute a notable zoonotic risk.
Multiple anthelmintics are available for treatment and prevention.
Multiple drug resistance in A caninum is an emerging problem in the southeast US.
All dogs and cats should be treated preventively for hookworms.
For More Information
Hookworms for Dogs. Companion Animal Parasite Council. Accessed October 3, 2022. https://capcvet.org/guidelines/hookworms/
Hookworms. Tropical Council for Companion Animal Parasites Ltd. Accessed October 3, 2022. https://www.troccap.com/canine-guidelines/gastrointestinal-parasites/hookworms/
Hookworms for Feline. Tropical Council for Companion Animal Parasites Ltd. Accessed October 3, 2022. https://www.troccap.com/feline-guidelines/gastrointestinal-parasites/hookworms-feline/
Endoparasites. European Scientific Counsel Companion Animal Parasites. Accessed October 3, 2022. https://www.esccap.org/parasites/Endoparasites/1\#c8
