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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.
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 either
cutaneous larva migrans or
eosinophilic enteritis. |
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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 either
A
caninum
or
A
braziliense
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. Arrested development may also occur in the mucosa of the small intestine. These arrested larvae are activated after removal of adult worms from the intestine or during pregnancy when they accumulate in the mammary glands. |
| 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
A
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. Neither
A
braziliense
nor
U
stenocephala
is an avid blood feeder, 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%. Hemorrhagic enteritis with a swollen intestinal mucosa that shows red, small ulcers and attached worms is usually seen in acute, fatal cases. |
| 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. |
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| Diagnosis: |
| The characteristic thin-shelled, oval eggs are easily seen on flotation of fresh feces from infected dogs. 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. |
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| 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 and drug combinations are approved for treatment of
A
caninum
and
U
stenocephala
infections: dichlorvos, fenbendazole, flubendazole, mebendazole, nitroscanate, piperazine, pyrantel, pyrantel/febantel, pyrantel/oxantel, and praziquantel/pyrantel/febantel. Milbemycin is also licensed for treatment of
A
caninum
infections (Table:
Drugs with Approved Activity Against Intestinal Helminths of Dogs and Cats). 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, milbemycin/lufenuron, and diethylcarbamazine/oxibendazole also controls
A
caninum
, while pyrantel/ivermectin controls
A
caninum
,
A
braziliense
, and
U
stenocephala
. 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 dichlorvos, flubendazole, mebendazole, milbemycin, piperazine, pyrantel, pyrantel/praziquantel, and selamectin (Table:
Drugs with Approved Activity Against Intestinal Helminths of Dogs and Cats). Dichlorvos, flubendazole, mebendazole, and piperazine are also approved for treatment of
U
stenocephala
infections. Heartworm prevention with ivermectin, milbemycin, and selamectin controls
A
tubaeforme
, while ivermectin also controls
A
braziliense
. |
| 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 (50 mg/kg, PO) given daily to pregnant bitches from day 40 of pregnancy to day 14 after whelping greatly reduces transmammary transmission to the pups. 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. |
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