Cutaneous larva migrans (CLM)

Etiologic agents = hookworms of dogs and cats

• Ancylostoma braziliense
• Ancylostoma caninum
• Uncinaria stenocephala (less commonly)

Infective hookworm larvae are acquired from soil that has been contaminated with feces from infected dogs or cats. The larvae directly penetrate a person's skin and cause a highly pruritic, "creeping eruption" with raised, red "tracks" and vesicles. Ancylostoma braziliense often produces dramatic, long migratory tracts/lesions. The other hookworms tend to cause shorter lesions.

• Systemic eosinophilia is less common than with visceral larva migrans. (See below)
• The lesions generally regress spontaneously, but can be treated successfully with thiabendazole, albendazole or ivermectin.

Human eosinophilic enterocolitis: This relatively rare condition occurs when hookworm larvae undergo a systemic migration in people to the gastrointestinal tract, leading to a syndrome of acute abdominal pain, anorexia, nausea and diarrhea.

• Ulceration of the terminal ileum and colon occurs, along with an eosinophilic inflammatory response.
  • Interestingly, patients generally do NOT have premonitory cutaneous larva migrans lesions.

Visceral larva migrans (VLM)

Etiologic agents = roundworms of dogs and cats

• Toxocara canis
  • Toxocara canis infections are extremely common (up to 90-100%) in puppies less than 3 months of age, and can also occur in older dogs. Furthermore, infected puppies can shed hundreds of thousands of eggs/defecation.
• Toxocara cati (less commonly)
  • There are also reports of VLM associated with Ascaris suum from pigs.

Visceral larva migrans occurs most commonly in young children with "pica" (eating non-food substances) and poor hygiene practices that allow for consumption of infective eggs from soil or soil/feces-contaminated foods or playthings. It is characterized by fever, malaise, wheezing and hepatomegaly, as well as a prominent leukocytosis, eosinophilia and hypergammaglobulinemia.

• VLM severity ranges from asymptomatic (2.8% of the US population are seropositive for exposure to these parasites) to fatal infections.
  • The larvae migrate from the GI tract to the liver via the portal circulation, then to the lungs and into the systemic circulation to reach virtually any organ in the body.

Ocular larva migrans (OLM)

Ocular larva migrans is essentially just visceral larva migrans affecting the eye, although in most cases, ocular larva migrans develops in the absence of signs of other visceral involvement. Manifestations may include retinal granulomas, retinal detachment and endophthalmitis and "diffuse unilateral subacute neuroretinitis syndrome" ("unilateral wipeout syndrome") with vision loss, vitritis and papillitis. OLM also deserves special mention because of the sad fact that the posterior chamber masses of ocular larva migrans in the eye have been misdiagnosed as a specific form of childhood ocular neoplasia called retinoblastoma. (Go to these 2 images and note how similar they can look to each other.) As such, children have needlessly suffered enucleation of an eye.

Treatment of VLM:

As with CLM, VLM may resolve spontaneously, but can be treated with anthelmintics (albendazole, mebendazole). The anthelmintics are generally accompanied by anti-inflammatory drugs (corticosteroids) to prevent intense inflammatory reactions to the dying larvae.

Prevention of larva migrans:

In cutaneous and visceral/ocular larva migrans, the nematode larvae involved MUST develop in the soil for a period of days before they are infective.

• Hence, transmission to humans is not associated with direct animal-human contact.

Nonetheless, the veterinarian has an important public health responsibility to advise clients of the zoonotic potential of these common nematodes, and to control these parasites at the individual pet and, ultimately, at the population level, through consistent programs of fecal testing and treatment.

• In a recent survey, however, fewer than 1/3 of veterinarians discussed the zoonotic aspects of these parasites with their clients.

Since virtually all puppies are infected from the dam, the CDC recommends that all puppies be wormed beginning at 2 weeks of age (much earlier than is usually done clinically) and that the dams be treated simultaneously.

The larvae of these nematodes can remain infective in the soil for months to years, so environmental contamination is a real problem. Every owner of a new puppy (or kitten) should be advised of the zoonotic potential of these parasites and the importance of their control.

Cuterebra myiasis
Cat and rabbits are commonly infected with rabbit or rodent botfly larvae of Cuterebra spp. However, humans can also be infected. Specifically, Cuterebra larvae have been recovered from subdermal nodules, eyes, nasal passages and oropharyngeal and tracheobronchial spaces in human beings.

Screwworm myiasis
The Cochliomyia hominovorax screwworms that threaten livestock populations are also occasionally isolated from cutaneous lesions or the eyes or nasal passages of human beings.

Canine whipworm infection of human beings

People have their own whipworm, Trichuris trichuria, but people are also infrequently infected with the canine whipworm, Trichuris vulpis (most commonly children or those with pica). Infections may be asymptomatic or may involve diarrhea, nausea, and abdominal pain.

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