by Chick Newman, PhD, DVM
Introduction: Hookworms are blood-sucking worm-parasites of the small intestine and, occasionally of the colon. The name refers to the hook-like mouth parts that are used to anchor themselves to the lining of the small intestine. In general, the worms are small (~1/8 inch long) and barely discernible to the naked eye. The species of concern are: Ancylostoma caninum, Uncinaria stenocephala, Ancylostoma braziliense all in dogs and Ancylostoma tubaeformae, as well as Ancylostoma braziliense in cats. Ancylostoma caninum is a potential zoonotic threat; Uncinaria stenocephala and Ancylostoma tubaeformae may be a zoonotic worry (the literature is conflicting). Most human infestations from these particular species result in cutaneous larval migrans. More about human zoonoses and canine hookworms can be obtained elsewhere.
Life Cycle: The life cycle of hookworms is illustrated, cryptically, here. Infection is via oral or cutaneous routes or...in neonatal puppies...via passage of infective larvae in the milk.
Clinical Signs: These worms can cause assymptomatic infestation or serious illness and even death. The cardinal sign of hookworm infestation is anemia and diarrhea (small intestinal or large intestinal (see comparison), depending on which part of the digestive tract is affected). Ancylostoma caninum is more pathogenic than Uncinaria stenocephala or Ancylostoma braziliense because is sucks much more blood. As the female worm is a prodigious egg producer, and egg survive in the environment best when the climate is temperate with moderate rainfall...Spring, Summer and early Fall...most infestations are seen during these months. There are several recognized clinical forms of Ancylostyoma-hookworm infestation:
Peracute Ancylostomosis: This results from passage of infective larvae to the nursing puppies in the milk, beginning four days from whelping. When as few as 50-100 larvae are ingested, puppies may appear relatively healthy the first week of life, but by the second week, they are ill thrifty with pale mucus membranes (from anemia and cardiovascular compromise due to dehydration), very soft-to-liquidy and quite dark feces. (The darkness is due to bacterial digestion of blood shed by the hookworms in the intestine.) . These cases generally can not be diagnosed via the fecal flotation method because the worms do not lay visible eggs until the 16th day after initial infestation. And the prognosis for survival, with or without treatment, is guarded. Death often occurs due to exsanguination!
Acute Ancylostomosis: This clinical form of hookworm infestation occurs in older pups and mature dogs who have been suddenly exposed to a large number of infective larvae. As eggs are not seen until day 16 after exposure, again, clinical signs may precede the appearance of eggs in a fecal flotation. Clinical signs vary from treatment-responsive anemia and diarrhea to death.
Chronic Compensated Ancylostomiasis: Animals are usually assymptomatic but moderate anemia is present. In some animals, a generalized ill thrifty appearance is also visible. Diagnosis is via the appearance of hookworm eggs in fecal flotation preparations and by the confirmation of anemia.
Secondary (decompensated) Ancylostomosis: Animals are sickly from other problems and their condition is further aggravated by concurrent hookworm infestation. Usually malnourished, emaciated and profoundly anemic, these animals can die from hookworm or non-hookworm related complications of their multifaceted medical problems.
Cutaneous Larval Migrans in Humans: This condition in humans is sometimes called "creeping eruption", and is also caused by Strongyloides, as described before. Ancylostoma braziliense is the most commonly involved species...but the other Ancylostoma species are also potential sources. Most cases originate on the beach of warm climates, such as the coastal areas of the southeast United States...the soft, damp sand readily harbors infective larvae and barefooted humans are likely to roam these beaches. As the larvae migrate in the skin (anywhere from a fraction of an inch to several inches per day), a very narrow, red (erythematous) linear formation is visible on the surface of the skin.
The area may become progressively raised with the appearance of vesicles (fluid-filled blisters), then crustiness. Some victims describe the itching as almost intolerable! It is worse in persons previously sensitized; re-exposure causes a hypersensitivity reaction, similar (but apparently a more intense form) to an allergic response. Humans do not get the intestinal form of hookworm...though migration through lungs may occur.
Diagnosis: Is accomplished readily via the fecal flotation technique. The microscopic appearance of eggs obtained this way is shown below. In some instances, clinical signs ensue before the prepatent period (time from initial exposure to the appearance of eggs). In those cases, it will be possible to only make a presumptive diagnosis.
Dichlorvos: 11mg/kg by mouth
Fendbendazole: 100 mg/kg by mouth or 50 mg/kg by mouth daily for 3 days
Mebendazole: 25 mg/kg by mouth daily for 3-5 days
Pyrantel: 20-30 mg/kg by mouth
Selamectin: 7-13 mg/kg topically
Thenium closylate: 100-200 mg/kg by mouth
Toluene: 0.22 mg/kg by mouth
Butamisole: 2.5 mg/kg subcutanously
Dichlorvos: 30 mg/kg by mouth
Diphosphenol: 2.2 mg/kg subcutaneously
Fendbendazole: 50 mg/kg by mouth daily for 3 days
Ivermectin: 0.05 mg/kg subcutaneously or by mouth
Mebendazole: 22 mg/kg by mouth daily for 3-5 days
Pyrantel: 5-10 mg/kg by mouth
Thenium closylate: 50 mg/kg by mouth --two doses 12 hours apart
Mibemycin oxime: 0.5 mg/kg by mouth...for Ancylostoma, not Uncinaria
Copyright© 1997-2017 Newman Veterinary Medical Services®, Seattle, WA
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