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Category: Clinical Microbiology
Tissue Nematodes, Page 1 of 2
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This chapter begins with a discussion on Trichinellaspp. Studies of isolates of Trichinella spp. from Arctic, temperate, and tropical areas have confirmed that there are major differences related to their genetic structure and overall biology. The chapter next focuses on Baylisascaris procyonis. There is no effective cure for B. procyonis infection; treatment is symptomatic and involves systemic corticosteroids and anthelmintic agents. An excellent review of the diagnostic morphology of four larval ascaridoid nematodes that may cause visceral larva migrans (VLM) include identification keys for Toxascaris leonina, Baylisascaris procyonis, Lagochilascaris sprenti, and Hexametra leidyi. VLM symptoms caused by Toxocara spp. must be differentiated from those caused by other tissue-migrating helminths (ascarids, hookworm, filariae, Strongyloides spp., and Trichinella spp.), as well as other hypereosinophilic syndromes. Diethylcarbamazine, thiabendazole, ivermectin, and albendazole are effective in some cases but not in others. Corticosteroids may also be given to patients with VLM or ocular larva migrans (OLM). Various reports were published during the late 1800s; however, it was not until 1926 that the most common etiologic agent of cutaneous larva migrans (CLM) in the southern United States was found to be Ancylostoma braziliense, a very common hookworm of dogs and cats. A. caninum, the common hookworm of dogs, has been implicated in cases of CLM. Other species are also capable of producing CLM, although they are less common than A. braziliense. The chapter also focuses on Dracunculus medinensis, Angiostrongylus cantonensis, and Thelazia spp.
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Life cycle of Trichinella spp. A number of infected meat sources other than pork are relevant for the various species of Trichinella.
Trichinella spp., encysted larva in muscle. (Illustration by Sharon Belkin.)
(A) Trichinella spiralis, encysted larva in muscle (×85). Adjacent muscle has been replaced by fibrous tissue and is infiltrated with chronic inflammatory cells. (Armed Forces Institute of Pathology photograph.) (B) Coiled larva of T. spiralis in a teased muscle preparation (wet mount, ×193). (Armed Forces Institute of Pathology photograph.)
Unencapsulated Trichinella pseudospiralis. (Image courtesy of the Centers for Disease Control and Prevention, Atlanta, Ga.)
Diagnosis of trichinosis.
Life cycle of Baylisascaris procyonis. Accidental infection in the human leads to visceral larva migrans (VLM), ocular larva migrans (OLM), and/or neural larva migrans (NLM), which are very serious diseases that can cause death. Infections are seen primarily in very young children.
Baylisascaris procyonis eggs; note the larvae within the egg shells. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Baylisascaris procyonis, CNS atrophy, sclerosis, and larval granuloma in the brain in a 2-year-old boy who died following 14 months of CNS problems. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of K. R. Kazacos.)
(A) Baylisascaris procyonis, larva in the brain of an 18-month-old boy who died after a 3-week bout of CNS disease. (B) Mesenteric granuloma from the same patient. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of K. R. Kazacos.)
Lagochilascaris minor egg; note the pits in the egg shell (somewhat similar to Toxocara eggs). (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Life cycle of Toxocara spp., the cause of visceral larva migrans (VLM) and ocular larva migrans (OLM).
Toxocara canis: (A) immature egg; (B) mature egg containing larva; (C) adult worms. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Diagnosis of toxocariasis.
Life cycle of Ancylostoma spp., the cause of cutaneous larva migrans (CLM).
Linear tracks caused by migration of Ancylostoma spp. (cutaneous larva migrans [CLM]). (From a Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Dracunculus medinensis, blister on leg (contains female worm); note removal of the adult worm. (Illustration by Sharon Belkin.)
Life cycle of Dracunculus medinensis, the cause of guinea worm disease.
Dracunculus medinensis, adult worm in subcutaneous tissues below the breast. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of J. Donges.)
Dracunculus medinensis, abscess caused by developing worm. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Dracunculus medinensis infection. Blisters develop in the skin, usually on the lower extremities, when the gravid female worm approaches the surface of the skin. (Armed Forces Institute of Pathology photograph.)
Female Dracunculus medinensis worm being removed by winding on a stick. (Armed Forces Institute of Pathology photograph; contributed by Everett L. Schiller, Johns Hopkins University School of Public Health, Baltimore, Md.)
Extraction of Dracunculus medinensis. The stick has been removed, and larvae have been squeezed from the flattened exterior portion of the worm. (Armed Forces Institute of Pathology photograph; contributed by Everett L. Schiller, Johns Hopkins University School of Public Health, Baltimore, Md.)
Life cycle of Angiostrongylus spp. [see (1) in figure]. Humans present with encephalitis when worms die in the brain tissue.
Angiostrongylus cantonensis in the central canal of the spinal cord. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Angiostrongylus cantonensis adult male worm in the eye. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.)
Life cycle of Gnathostoma spinigerum.
Gnathostoma spinigerum, adult worm. [Illustration by Sharon Belkin; adapted from reference 10 ; originally adapted from I. Miyazaki, Studies on Gnathostoma occurring in Japan (Nematoda: Gnathostomidae). II. Life history of Gnathostoma and morphological comparison of its larval forms, Kyushu Mem. Med. Sci. 5: 123–140, 1954.]
Head of adult gnathostoma. (Armed Forces Institute of Pathology photograph.)
Life cycle of Anisakis, Contracaecum, Pseudoterranova, Hysterothylacium, and Porrocaecum spp. (larval nematodes acquired from saltwater fish).
Scanning electron micrograph of an Anisakis simplex larva penetrating human stomach tissue in vitro. Note the tunnel created in the mucosa and the burrow in the submucosa. (Reprinted with permission from J. A. Sakanari and J. H. McKerrow, Identification of the secreted neutral proteases from Anisakis simplex, J. Parasitol. 76: 625–630, 1990.)
(A) Anisakis in fish flesh. (B) Larval nematodes in fish viscera. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of L. A. Jensen.)
Capillaria hepatica eggs in liver. (From A Pictorial Presentation of Parasites: A cooperative collection prepared and/or edited by H. Zaiman.) For information on intestinal capillariasis with Capillaria philippinensis, see chapter 10.
Characteristics of Trichinella species
Trichinella spp.: encapsulated and nonencapsulated species a
Tissue nematodes
Trichinella spiralis: life cycle stages and clinical conditions a
Trichinosis: incubation period, larval numbers, and degree of illness
Outbreaks due to consumption of Trichinella spp. in horse meat a
Trichinellosis: prevention and control measures
Differential diagnosis of Baylisascaris procyonis infection