Baylisascaris procyonis Caused Meningitis.

by CL

Society today has become overly sterilized. Antibiotic hand soaps and disinfectants can be found in many American households and business and it seems that people are increasingly afraid of getting "dirty". This trend has become severe enough that in the late 1980's Dr. Strachan formulated the "Hygiene Hypothesis", which suggests that a decrease in exposure to infectious agents causes an increase in atopic diseases [1]. A good way for people, especially children, to become exposed to microorganisms is for them to eat food that has been on the ground since there can be up to 2,000 bacterial species in half a gram of Minnesotan soil [2]. That being said there are times when eating the cookie that fell on the ground is a very bad idea. One of the worst times for this would be when there is a chance that raccoons have recently defecated on that spot. The ingestion of raccoon fecal matter should be avoided because raccoons are the definitive host for Baylisascaris procyonis. More commonly known as the raccoon roundworm B. procyonis is a helminth that can be found in up to 70% of raccoons and can cause severe disease in humans [3].

Figure 1. Basic diagram of the B. procyonis

lifecycle, including other host organisms.

B. procyonis lives and mates inside the intestines of raccoons and when the animals defecate millions of unembryonated eggs are released into the environment; in two to four weeks larvae form within the eggs and they become infectious [3, 4]. B. procyonis eggs tend to be resistant to environmental degradation and given adequate moisture they can remain viable and infectious for years. This increases the chances for the organism to complete its life cycle by infecting another raccoon; however, it also increases the likely hood of a person becoming infected after accidental ingestion [3]. Once inside a human host larvae can disseminate throughout the body in as little as three days and seven percent or more of larvae can cross the blood brain barrier to infect the CNS. Once inside the CNS the larvae will molt and grow, which tends to produce irritability, fever, lethargy, and other symptoms similar to bacterial meningitis, in the infected person [3]. It is only through the discovery of high levels of eosinophils in the CNS that a positive diagnosis of eosinophilic meningitis is made. Eosinophils are white blood cells that are commonly found in parasitic infection associated with helminths and other worm infections. The use of antihelminth drugs early in the infection may help to reduce the severity of disease, but poor outcomes are still common and living larvae have been recovered from brain autopsies of treated animals and humans [3]. The severity of meningitis caused by B. procyonis infection is partly due to the fact that the larvae molt and grow as they migrate, which leads to an increased risk of permanent neurological damage in treated cases [5].  The amount of inflammation caused by the organism and the high levels of eosinophils found in the CNS also contribute to the poor prognosis of the disease [3]. Due to the fact that humans are dead end hosts for B. procyonis the organism cannot complete its lifecycle and cannot be spread between people. Also since the organism cannot reproduce inside humans the parasite cells will die and the infection will eventually clear itself, but permanent neurological damage and/or death is likely to occur before this can happen [1].

Figure 2. Adult worms next to a

dime for scale. The size of the

worms is part of the reason for

the disease severity and neurological

complications. Female worm is

 on left, male is on right.

The limited means of transmission keeps Baylisascaris procyonis infections down; however, public knowledge about this organism and its potential to cause severe disease in children will help to minimize infection rates. With an alarmingly high rate of up to 70% of raccoons carrying B. procyonis in some areas and an estimated 800,000 to 1,000,000 raccoons in the state of Minnesota alone the environment is saturated with raccoon feces and B. procyonis eggs [3, 6]. This doesn't mean that exposure to the outside should be limited or that children should not be allowed to get dirty. Instead it means that the general population should be aware of the risks and take steps to prevent the accidental ingestion of raccoon fecal matter. The prevention of infection with Baylisascaris procyonis is as simple as discouraging raccoons from spending a lot of time if residential yards; which is simply done by covering trashcans, not indirectly feeding raccoons by leaving out pet food, or directly feeding raccoons or encouraging them in any way. Those steps alone won't guarantee that an infection never happens, but they will go a long way to decrease the chances of one. That being said if the raccoon population is particularly high in a residential area it is probably a good idea to wash off any food that has been on the ground before eating it.

Citations

1. Bloomfield, S.F., Stanwell-Smith, R., Crevel, R.W.R., Pickup, J. (April 2006). Too clean, or not too clean: the Hygiene Hypothesis and home hygiene. In Clinical and Experimental Allergy. (Vol. 36). (pp. 402-425). Blackwell Publishing Ltd.

2. Schloss, P.D., Handelsman, J. (2006). Toward a census of bacteria in soil. In PLoS Computational Biology. (Vol. 2). (Issue 7). (pp. 786-793). Retrieved online from http://www.ploscompbiol.org/article/info%3Adoi%2F10.1371%2Fjournal.pcbi.00 20092

3. Park, S.Y., Glaser, C., Murray, W.J., Kazacos, K.R., Rowley, H.A., Fredrick, D.R., Bass, N. (2000). Raccoon Roundworm (Baylisascaris procyonis) Encephalitis: Case Report and Field Investigation. In Pediatrics: The Official Journal of The American Academy of Pediatrics. (Vol. 106). (Number 4.) Elk Grove Village, Illionis: American Academy of Pediatrics.

4. CDC. (Oct. 11, 2012). Parasites - Baylisascaris infection. In Centers for Disease Control and Prevention. Retrieved Nov. 16, 2012, from http://www.cdc.gov/parasites/baylisascaris/biology.html.

5. Dangoudoubiyam, S., Kazacos, K.R. (Nov. 2009). Differentiation of Larva Migrans Caused by Baylisascaris procyonis and Toxocara Species by Western Blotting. In American Society for Microbiology: Clinical and Vaccine Immunology. (Vol. 16). (Number 11.) (pp. 1563-1568). Washington DC: American Society for Microbiology.

6. Minnesota DNR. (2012). Raccoon. In Minnesota Department of Natural Resources. Retrieved Nov. 16, 2012, from http://www.dnr.state.mn.us/mammals/raccoon.html.