Raccoon Roundworm

The Life Cycle

The raccoon roundworm is a common intestinal parasite found in raccoons. The percentage of raccoons infected varies from 40% to 100% depending on the density of the raccoon population. The adult worm lives in the intestines of the raccoon and sheds microscopic eggs. A single defecation may carry anywhere from a few thousand to millions of the microscopic eggs! The eggs reach infectivity stage in 3 to 4 weeks after being deposited. Raccoons defecate in localized areas called ´┐Żlatrines.´┐Ż These are usually located in elevated surfaces, but can be anywhere. The eggs can infect immediate hosts such as birds, rodents, rabbits, dogs, cats, and other mammals as well as humans. After being ingested, the roundworm eggs hatch into larvae which migrate within the host. These larvae burrow through the walls of the hosts’ intestine, migrate to the liver, lungs and from there to various other organs before changing into a cyst form. Some infected animals become sick. However, when a raccoon feeds on an intermediate host such as a squirrel, the cysts open and grow into egg-shedding adult roundworms in the raccoon’s intestine and the cycle begins again. The raccoon is relatively unaffected and appears normal. A few may die of intestinal blockage or rupture from heavy infection.

The Eggs

The raccoon roundworm eggs are some of the most resistant parasites known. The outer covering of the egg stick to any type of surface! The egg is resistant to disinfectants although certain solvents will kill them. Bleach can remove the outer protein coat making the eggs nonadherent but does not kill the egg itself. The eggs continue to contaminate an area for years even after harsh winters. The most effective way to destroy the eggs is through incineration or the use of a portable propane torch used in a safe manner on all contaminated surfaces. Surface soil can be turned over several times with a rake or shovel and reflamed each time. It may be necessary to remove or bury the soil. Dried raccoon feces always should be burned.

The Raccoon Roundworm Infection

After accidental inhalation or ingestion of the raccoon roundworm by a human, the growing larvae can become very dangerous to the liver, lungs, and heart as the larvae lengthen and move. The condition is called larva migrans in humans. Raccoon roundworm has a tendency to migrate to the eye and the brain. The larvae stops migrating within weeks, and then encapsulate into the cyst form. The more eggs ingested the more aggressive the migrating larvae are thought to cause serious inflammatory reactions. The prevalence in humans of raccoon roundworm infections is therefore unknown due to the difficulty of diagnosis. Only five reported fatal cases have been documented in medical literature since 1981. The potential for infection may be high. Mild forms may be unsuspected when the larvae encapsulate in the skeletal muscle or connective tissue. A person exposed and having symptoms such as cough, fever, drowsiness, confusion, loss of muscle coordination, decreased head control, visual disturbance, central nervous system or meningitis should alert their physician to the possibility of infection with raccoon roundworm. An antibody blood test used with animals may soon be available for humans.

Young children are thought to be the most susceptible to this parasite since they are more apt to put objects, soil, or contaminated fingers into their mouths. The infant toddler may be the most at risk as well as trappers and wildlife rehabilitators. The migrating larvae are most readily seen in the eye by the physician. Humans have suffered permanent nervous system or vision disabilities, and in severe cases blindness, coma, and death have occurred. Prevention is the only to combat the disease.

A Case History

In 1998, an abnormally high raccoon population existed within a small California town only a few square miles. An eleven month old boy living there developed a life threatening infection with raccoon roundworm. This child at times played under his trees with protective concerned parents. His symptoms started out with irritability and quickly progressed to tremors in his arms and the inability to sit up. His first hospitalization found no cause for the symptoms, but the next day he was hospitalized for more than six weeks. He was finally diagnosed with larvae migrans by the raccoon roundworm. He presently is visually handicapped with brain damage, unable to walk or talk, and need of 24 hour care at home. He is not expected to recover. The high dencity population of raccoons is associated with residents of an area feeding raccoons. A trapping and testing program in the community found over 98% of the trapped and tested raccoons were positive for the raccoon roundworm in the town. Only a few human cases have been identified throughout the United States and California. Diagnosed cases are few considering the number of raccoons living in rural and urban settings. It is suspected that there are many other unknown cases with less sever symptoms or with erroneous diagnosis. Dog or cat roundworm infection is thought to be much more common.

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