Kvet Forum
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All farm animals other than horses harbor hookworms. The main species are the following:
- Cattle: Bunostomum phlebotomum is the most widespread but Agriostomum vryburgi may occur in cattle in Asia and South America.
- Sheep: B. trigonocephalum is found worldwide, whereas Gaigeria pachyscelis occurs in India, Indonesia, South America, and Africa.
Life Cycle
Hookworms are reddish-colored nematodes, 1 to 2.5 cm long, and inhabit the small intestine of their hosts. The females are prolific egg layers and the life cycle is direct. The eggs hatch and two free-living, nonparasitic larval stages follow, which are very susceptible to desiccation. An infective larva is produced in about 1 week under favorable conditions. Transmission is by skin penetration alone in the case of G. pachyscelis but Bunostomum spp. larvae can enter the body via the skin or the mouth. After cutaneous penetration, larvae do the following:
- Enter the bloodstream.
- Are carried to the heart and lungs.
- Enter the alveoli in which the fourth-stage larvae develop.
- Move up the air passages to the pharynx.
- Are swallowed.
- Reach the small intestine.
The chances of infestation occurring by percutaneous entry are greatly enhanced when the surroundings are wet thereby minimising chances of the larvae to dessicate.
Hookworms are active bloodsuckers and cause severe anemia in all animal species. There is a loss of whole blood and hypoproteinemic edema may result. Some irritation to the intestinal mucosa is inevitable and mild or intermittent diarrhea follows. Penetration of the skin by larvae may cause signs of irritation and lead to the introduction of pathogenic bacteria.
Clinical Findings
In mild infestations in stabled cattle, fidgeting, stamping, and licking of the feet may be observed. Constipation, accompanied by mild abdominal pain, is seen in the early stages and is followed by bouts of diarrhea. The cattle are unthrifty and anemic. In severe infestations there is obvious pallor of mucosae, weakness, swelling under the jaw and along the belly, prostration, and death in 2 to 3 days.
The signs in sheep are similar to those in cattle. The convalescent period, even after treatment, is prolonged unless the diet is supplemented to stimulate erythrocyte production.
Because both larvae and adult worms are avid bloodsuckers, clinical signs are often evident before eggs appear in the feces. The degree of anemia and the presence of occult blood in the feces can be used as a measure of the severity of the infestation.
At necropsy, most of the worms are found in the first few feet of the small intestine, and the intestinal contents nearby are often deeply bloodstained. B. trigonocephalum in sheep has been observed to be localized predominantly in the jejunum and ileum. Hookworms often form part of a mixed infection comprising several or many gastrointestinal nematodes.
Treatment
Cattle
- Ivermectin, doramectin, or moxidectin (0.2 mg/kg SQ)
- Eprinomectin (0.5 mg/kg Topical)
- Albendazole (10 mg/kg PO)
- Febantel (7.5 mg/kg PO)
- Fenbendazole (5 mg/kg PO)
- Oxfendazole (4.5 mg/kg PO)
- Levamisole (7.5 mg/kg O; 10 mg/kg Topical)
Sheep
- Ivermectin, doramectin, or moxidectin (0.2 mg/kg SQ or PO)
- Albendazole (7.5 mg/kg PO)
- Febantel (5 mg/kg PO)
- Fenbendazole (5 mg/kg PO)
- Oxfendazole (5 mg/kg PO)
- Mebendazole (15 mg/kg PO)
- Levamisole (7.5 mg/kg PO)
Control
Wet surroundings such as in pastures and grazing yards should be avoided to reduce the chances of percutaneous infestation and reduce the viability of the free-living larvae. Pens should be cleaned frequently and ample bedding provided. Heavy stocking of sheep or calves in small pens should be avoided. Under conditions of heavy risk, periodic treatment should be administered.