Raccoon roundworm cases investigated in Los Angeles County
The Los Angeles County Department of Public Health is investigating two human cases of a rare parasitic infection, Baylisascaris procyonis, also known as raccoon roundworm. The two cases were found in the South Bay area of Los Angeles County.
What is Baylisascaris procyonis?
Also known as the raccoon roundworm, B. procyonis is the most common and widespread cause of clinical larva migrans in animals. It is a ubiquitous roundworm infection of raccoons (Procyon lotor) and is emerging as an important helminthic zoonosis, primarily in young children.
Baylisascaris procyonis and related species are large nematodes of the order Ascaridia. Other, more familiar ascarids are Ascaris lumbricoides, Toxocara canis and Toxocara cati, nematode parasites of humans, dogs and cats, respectively.
Infection in Animals
The raccoon roundworm is indiscriminate in what animals it can infect, with more than 90 species of wild and domestic animals being identified as infected with B. procyonis larvae. Outbreaks of fatal central nervous system disease have occurred on farms, in zoos and research animal colonies and have affected commercial chickens, quail, pheasants and domestic rabbits. Many times these animals get infected by getting the eggs in their fur and then ingesting the eggs during grooming. In nature, small birds and mammals (particularly rodents) are infected by ingesting infective B. procyonis eggs while foraging for food at preferred sites of raccoon defecation.
When a species of animal other than a raccoon swallows these eggs, the microscopic larva hatches out in the intestine and then burrows through the wall of the intestine and begins migrating through the body trying to find a home. The body tries to kill the larva and it moves rapidly to escape attack. The larva seems to have a preference for lodging in the liver, eyes, spinal cord or brain. Occasionally, they can be found in other organs. When a larva tries to make a home, it causes a great deal of damage as the body tries to either wall it off or kill it. Eventually it dies and is reabsorbed by the body. In very small species such as mice, it might take only one or two larvae in the brain to be fatal. If the larva does not cause significant damage in vital organs, then the victim will show no signs of disease. Species other than the raccoon that are affected with this parasite CANNOT pass it on to anyone else. This is the end of the line for the larva and it never becomes a mature adult capable of producing eggs.
B. procyonis in Raccoons
Baylisiascaris procyonis is indigenous in North American raccoons that are very common in rural, suburban and urban settings where they are well adapted living alongside humans. Raccoons thrive in areas where there is a permanent water supply, available food, and suitable sites for dens. Some of the highest raccoon densities are in and around suburban and urban residences and parks. Gardens, garbage cans, bird feeders and pet food provide ample food for the raccoon.
In North America, the prevalence of Baylisascaris procyonis in raccoons is highest in the Midwest and Northeast where an infection rate of up to 80% has been reported. In the Southeast where the risk is lower, Baylisascaris procyonis is becoming an emerging infection in raccoons.
Baylisascaris procyonis causes little to no clinical disease in the raccoon. They become infected in one of two ways: 1) Young raccoons become infected by ingesting eggs during exploring and grooming activities with other members of their social group; 2) Adult raccoons acquire the infection by ingesting intermediate hosts (rodents, rabbits, birds) infected with the larvae of B. procyonis. The disease in the intermediate hosts listed above makes them easy prey for raccoons.
Raccoon Latrines
Raccoons habitually defecate in communal sites called latrines. This can be natural or man-made structures. Common urban and suburban sites are rooftops, attics, in and around chimneys, tree stumps, woodpiles, decks and lawns (near trees). If there are many raccoons in the area, there are likely to be large amounts of resistant B. procyanis eggs in the area. In the raccoon, adult females produce approximately 150,000 eggs/worms/day. The average raccoon sheds an average of 20,000 eggs per gram of feces. Because of the quantity and the resistance to environmental conditions, it is possible to have heavy and widespread contamination.
Risk to Humans and Disease
There are two factors that put people at risk for infection: 1) contact with raccoons, their feces, or the contaminated environment and 2) geophagia of pica. Humans who accidentally come into contact with active or abandoned latrines are at risk. Young children are at particular risk because of the habit of placing their fingers or objects in their mouths.
Larval migrans is the prolonged migration and persistence of helminth larvae in the organs and tissues. Disease manifestations of human baylisascaris include visceral, neural and ocular larva migrans.
The clinical manifestations of severe disease include eosinophilic encephalitis, permanent neurological damage, ocular disease and blindness, and death.
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Diagnosis
There is no routine laboratory test considered diagnostic for B. procyonis alone. Typically, clinical illness, exposure history and an examination of the CSF for eosinophils are used. The use of magnetic resonance imaging is also useful. The use of serological tests can demonstrate anti-baylisascaris antibodies in serum and CSF. Indirect immunofluorescence, ELISA and western blot are available at specialized veterinary laboratories. Ocular examinations may show larval tracks or the larva itself.
Examination and identification of the larvae in biopsy material is possible; however, this requires experience in recognizing larval morphological characteristics and the ability to differentiate from other nematodes such as T.canis, T. cati and A. lumbricoides, among others.
Treatment
The preferred medication to treat baylisascariasis is albendazole. If albendazole is not immediately available, mebendazole or ivermectin may be used in the interim. Treatment should be initiated as soon as possible after ingestion of infectious material, ideally within three days.
Prevention and decontamination
The best, most effective way to prevent infection with B. procyonis is not keeping raccoons as pets and avoiding contact with their feces. Learn to recognize raccoon latrine areas and either stay away from them or clean them up if necessary. Favorite spots are at the bases of trees, in the forks of trees, on fallen logs, large rocks, woodpiles, decks, in attics, garages, chimneys, barns and outbuildings. In addition, raccoons like to nest in haylofts and may contaminate hay or straw that is used for bedding or food. Purchase hay or straw from a clean source and dispose of any bales that show evidence of fecal contamination. Do not store the hay you buy in areas with access to raccoons. Be cautious using and handling fallen timber for firewood. Also monitor children closely in potentially contaminated areas. Cover backyard sandboxes and block access routes for raccoons (mothballs are known to be effective). Do not feed the animals and secure garbage.
If you have a raccoon latrine on your property, cleaning it can be very challenging. Baylisascaris procyonis eggs are very resistant to the environment and can survive for years. They are resistant to all common disinfectants including bleach. The best way to kill the eggs is through flaming the area (including soil) or burning affected material such as straw or wood cages. Alternately, boiling water can be poured over small areas at a time. In heavily contaminated areas, it may be necessary to remove and bury the soil in a deep spot elsewhere. When cleaning up any latrine area, proper protection is a must. The protection should include a dust mask over the nose and mouth, disposable clothing, disposable gloves and heavy rubber boots that can be cleaned with boiling water.
Los Angeles County health officials say while Baylisascariasis is rare in people and the risk to the general public is low at this time, it is concerning because a large number of raccoons live near people, and the infection rate in raccoons is likely high. The confirmed cases of this rare infection are an important reminder for all in Los Angeles County residents to take precautions to prevent the spread of disease from animals to people, also known as zoonotic disease.