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Ancylostoma caninum is the principal cause of canine hookworm disease in most tropical and subtropical areas of the world. A tubaeforme of cats has a similar but more sparse distribution. A braziliense of dogs and cats is sparsely distributed from Florida to North Carolina in the USA. It is also found throughout Central and South America and Africa. Uncinaria stenocephala is the principal canine hookworm in cooler regions; it is the canine hookworm in Canada and the northern fringe of the USA, where it is primarily a fox parasite. U stenocephala also is seen in cats. A caninum males are ~12 mm long, females, 15 mm; the other species are somewhat smaller. The infective larvae of canine hookworms, particularly those of A braziliense, may penetrate and wander under the skin of people and cause cutaneous larva migrans.
The elongate (>65 μm), 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 hr on warm, moist soil. Transmission may result from ingestion of infective larvae from the environment or, in the case of A caninum, via the colostrum or milk of infected bitches. Infections with A caninum, A braziliense, or A tubaeforme can also result from larval invasion through the skin, but this route is of little significance for U stenocephala. Skin penetration in young pups is followed by migration of the larvae through the blood to the lungs, where they are coughed up and swallowed to mature in the small intestine. However, in animals >3 mo old, A caninum larvae, after migration through the lungs, are arrested in the somatic tissues. These arrested larvae are activated during pregnancy, then accumulate in the mammary glands. Arrested development may also occur in the mucosa of the small intestine; activation may occur after removal of adult worms from the intestine.
Clinical Findings
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 lesser 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 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 result when caninum shift feeding sites. The amount of blood loss due to a single worm in 24 hr 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 with some fatty infiltration of the liver. Hemorrhagic enteritis with a swollen intestinal mucosa that shows red, small ulcers and attached worms is usually seen in acute, fatal cases. A braziliense, A tubaeforme, 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 reduce blood protein by >10%.
Dermatitis due to larval invasion of the skin may be seen with any of the hookworms but has been seen most frequently in the interdigital spaces with U stenocephala. Pneumonia and lung consolidation may result from overwhelming infections in pups.
Diagnosis
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 μm; Uncinaria sp 71–92 × 35–58 μm). Acute anemia and death from infections acquired via milk may be seen in young pups before eggs are passed in their feces, ie, as early as 1–2 wk of age.
Treatment and Control
Bitches should be free of hookworms before breeding and kept out of contaminated areas during pregnancy. Bitches should whelp and the pups suckle in sanitary quarters. 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).
In dogs, the following drugs are approved for treatment of A caninum and U stenocephala infections: fenbendazole, moxidectin, nitroscanate, and pyrantel. Milbemycin is also licensed for treatment of A caninum infections (see Gastrointestinal Parasites of Small Animals: Drugs for Intestinal Helminths of Dogs Approved in the USA and UK ). When anemia is severe, chemotherapy may have to be supported by blood transfusion or supplemental iron, and followed by a high-protein diet until the Hgb level is normal. Heartworm prevention with milbemycin or milbemycin/lufenuron controls A caninum, while 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 Gastrointestinal Parasites of Small Animals: Drugs for Intestinal Helminths of Dogs Approved in the USA and UK) and are approved for this purpose. Finally, the injectable formulation of moxidectin for heartworm prevention in dogs also has significant efficacy against infection with A caninum and U stenocephala for at least 3 mo.
In cats, drugs approved for treatment of A tubaeforme include emodepside, fenbendazole, ivermectin, milbemycin, moxidectin, pyrantel, and selamectin (see Gastrointestinal Parasites of Small Animals: Drugs for Intestinal Helminths of Cats Approved in the USA and UK). Heartworm prevention with ivermectin, milbemycin, milbemycin/praziquantel, moxidectin/imidacloprid, or selamectin controls A tubaeforme, while ivermectin also controls A braziliense (see Gastrointestinal Parasites of Small Animals: Drugs for Intestinal Helminths of Cats Approved in the USA and UK).
When neonatal pups die due to hookworm infection, subsequent litters from the bitch should be treated weekly for A caninum for ~12 wk beginning at 2 wk of age. In addition, fenbendazole (25 mg/kg, PO) given daily to pregnant bitches from day 40 of pregnancy to day 2 after whelping greatly reduces transmammary transmission to the pups (licensed in the UK). Likewise, treatment of the bitch with ivermectin (0.5 mg/kg) on 2 occasions (4–9 days before whelping and 10 days later) has the same effect (extra-label use).
Last full review/revision March 2012 by Andrew S. Peregrine, BVMS, PhD, DVM, DEVPC
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