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12 : Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern

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Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern, Page 1 of 2

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Abstract:

The extraordinary heteroxenosity (ability to use many hosts in its life cycle) of is of particular concern not only to wildlife biologists but also to public health professionals and medical practitioners. To understand why there is an increasing human risk for infection with , a discussion of the biology and behavior of raccoons is prerequisite to subsequent discussions of epidemiology, pathogenesis, clinical features, diagnosis, and treatment. is the large ascarid parasite of raccoons. The biology, morphology, and ecology of are similar to those of other ascarid parasites of carnivores, such as the common canine roundworm, . Humans become infected with just as these other hosts do and become accidental hosts following inadvertent ingestion of eggs containing infective larvae. Without question, the biggest contributing factor to the poor response to neural larva migrans (NLM) therapy is treatment delay due to failure to add this zoonosis to the list of differential diagnoses. The problem of urbanized raccoons exemplifies the growing disconnect between the public's conceptions about wildlife and the reality of the public health risks that uncontrolled wildlife can pose. Accurate assessment of the prevalence of human exposure to would be of significant public health value and would begin to answer the numerous questions that remain about the epidemiology of baylisascariasis.

Citation: Murray W. 2004. Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern, p 159-175. In Scheld W, Murray B, Hughes J (ed), Emerging Infections 6. ASM Press, Washington, DC. doi: 10.1128/9781555816995.ch12
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Figure 1

A young raccoon prowling around an urban house at night in northern California. Large numbers of raccoons thrive in suburbia throughout North America and in other countries where they have been introduced. Note the forepaws (see text). Image captured by infrared flash trigger. (Photograph © 1999 William J. Murray.)

Citation: Murray W. 2004. Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern, p 159-175. In Scheld W, Murray B, Hughes J (ed), Emerging Infections 6. ASM Press, Washington, DC. doi: 10.1128/9781555816995.ch12
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Image of Figure 2
Figure 2

Adult nematodes removed from the small intestine of a raccoon. Adult females (left) are about 24 cm long, whereas the smaller males (right) are about 12 cm long. (Reprinted from reference with permission from Elsevier Science. © 2002 Elsevier Science.)

Citation: Murray W. 2004. Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern, p 159-175. In Scheld W, Murray B, Hughes J (ed), Emerging Infections 6. ASM Press, Washington, DC. doi: 10.1128/9781555816995.ch12
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Image of Figure 3
Figure 3

Life cycle of . ( ) Ingestion of infective stage eggs by young raccoons occurs as a consequence of their close association with infected adults. The eggs hatch in the intestinal lumen, releasing larvae that continue to develop in the mucosa of the intestine; they then reenter the lumen and develop into adults that mate, and the females begin shedding fertilized eggs. This entire process requires about 60 days from the time eggs are ingested. ( ) Although an intermediate host is not required for to complete its life cycle, older raccoons can become infected by consuming the flesh of a wide variety of host animals that become infected through feeding activities at latrine sites. The resulting visceral migration by larvae in the somatic tissues of these intermediate hosts frequently leads to neural larva migrans and severe CNS disease, making them easy prey for foraging raccoons. Once ingested by the raccoon, larvae encysted in the host's tissues are released in the adult raccoon's intestine where they develop into adults in about 35 days. ( ) Humans become accidental hosts following inadvertent ingestion of eggs containing infective larvae. Young children are the most frequently affected due to poor hygienic habits, geophagia, and their well-known propensity to play with and mouth objects found in the environment. (Reprinted from reference with permission from Elsevier Science. © 2002, Elsevier Science.)

Citation: Murray W. 2004. Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern, p 159-175. In Scheld W, Murray B, Hughes J (ed), Emerging Infections 6. ASM Press, Washington, DC. doi: 10.1128/9781555816995.ch12
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Image of Figure 4
Figure 4

Photomicrograph of a egg containing a fully formed infective larva recovered from a latrine in a playground sandbox (magnification, ×32). eggs can be differentiated from other ascarid eggs commonly found in the environment, such as those of , , and species, by expert examination. Briefly, eggs are ellipsoid, approximately 75 × 60 µm in size with a brown, finely granular surface.

Citation: Murray W. 2004. Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern, p 159-175. In Scheld W, Murray B, Hughes J (ed), Emerging Infections 6. ASM Press, Washington, DC. doi: 10.1128/9781555816995.ch12
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Image of Figure 5
Figure 5

Photomicrograph (magnification, ×32) of a living larva emerging from an egg that had been stored in 10% formalin for over 4 months, demonstrating the astounding resistance of ascarid eggs to destruction. During preparation of the specimen for photomicroscopy, manipulation of the cover slip cracked the egg open, freeing the larva. (Photograph © 1998 William J. Murray.)

Citation: Murray W. 2004. Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern, p 159-175. In Scheld W, Murray B, Hughes J (ed), Emerging Infections 6. ASM Press, Washington, DC. doi: 10.1128/9781555816995.ch12
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Figure 6

Human brain biopsy sample (hematoxylin and eosin stain; magnification, ×140). This fine-needle aspirate was removed from the brain of an adolescent boy with severe CNS disease. A larva is clearly visible in cross section (at midbody level) at the edge of the tissue section. larvae can be easily distinguished from the larvae of and spp. Diameters of and , which may also cause larva migrans, typically are from 17 to 21 μm or sometimes slightly smaller. In addition to the large size (60 to 70 μm in diameter) of larvae, conspicuous features are the prominent lateral alae on opposite sides of the cuticle and large excretory columns adjacent to the centrally located intestine. Photomicrograph courtesy of Lawrence R. Ash, UCLA School of Public Health. (Reprinted from reference with permission from Elsevier Science. © 2002, Elsevier Science.)

Citation: Murray W. 2004. Raccoon Roundworm Infection (Baylisascariasis): a Zoonosis of Pediatric and Public Health Concern, p 159-175. In Scheld W, Murray B, Hughes J (ed), Emerging Infections 6. ASM Press, Washington, DC. doi: 10.1128/9781555816995.ch12
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