We found 127 raccoon latrines on 80 properties in Pacific Grove, 64 latrines on 38 properties in Carmel, and 53 latrines on 46 properties in San Jose, for a total of 244 latrines on 164 properties. Property sizes were more variable in Pacific Grove (1,828 + 6,023 m²) than in Carmel (777 + 1,263 m²) or San Jose (752 + 447 m²). The density of latrines was 8.7/hectare (3.5/acre) in Pacific Grove, 21.7/hectare (8.8/acre) in Carmel, and 15.3/hectare (6.2/acre) in San Jose. In Pacific Grove and Carmel, we found most latrines on roofs (39%-41%); in San Jose most were located on the ground (54%) (Figure 4).

Of the 244 latrines, 29 were not accessible for sampling due to their unsafe locations, e.g., on damaged roofs. We examined the remaining latrines for B. procyonis eggs, and approximately half (44.0%-53.2%) of these were positive, with many containing infective eggs (15.9%-31.5%) (Figure 5). Nearly half of the properties in Pacific Grove and Carmel (47.4%-48.8%) and more than one quarter of those in San Jose (28.0%) contained at least one latrine that was positive for B. procyonis eggs (Figure 6). Over half of the properties in San Jose (54%) and more than one fourth in Pacific Grove and Carmel (27%-28%) did not harbor latrines. Most of the properties examined had three or fewer latrines, but a few contained as many as eight (Figure 7).

The widespread distribution and high densities of latrines suggest that human and animal contact with raccoon feces and B. procyonis eggs is likely to be common in the study areas. However, human clinical infections are uncommon, probably because most persons do not have intimate contact with the sites or exhibit those behaviors (ingestion, pica, geophagia) that would result in heavy infection. Nonetheless, the potential for infection exists, especially for young inquisitive children who might exhibit such behaviors. Moreover, because of the widespread distribution of raccoons, as well as diagnostic difficulties and lack of clinical experience with the spectrum of disease caused by B. procyonis in humans, mild or subclinical infections likely go unrecognized. In fact, asymptomatic, low-level infection with B. procyonis is probably the most common form of infection (1–3,6).

These study sites had greater densities of latrines and a higher percentage of latrines containing B. procyonis eggs than seen in previous studies. Page et al. (12) found 42 latrines in an 8.2-hectare woodlot (5.5/hectare) in Indiana and B. procyonis eggs in 14% of the latrines sampled. Jacobson et al. (20) found 97 raccoon scats in a 280-hectare urban study area and 121 raccoon scats in a 230-hectare rural study area in Indiana (0.35 and 0.53/hectare, respectively). They also found that 27% of the urban scats and 31% of the rural ones contained B. procyonis eggs (20).

The latrine densities found in our study sites suggest an abundant raccoon population. This conclusion is further supported by field observations of large numbers of raccoons encountered during the surveys. As raccoon density increases, opportunities for intra- and interspecific density-dependent disease transmission also increase. Intraspecific transmission occurs when B. procyonis eggs pass from one raccoon to another through social interactions, such as living in the same den and grooming, and by visits to latrines. Interspecific transmission involves intermediate hosts; small granivorous rodents and birds routinely ingest roundworm eggs as they forage for seeds contained in raccoon feces at latrines (2,13,14). The possibility of transmission increases with higher latrine density.

Urban environments typically provide increased food sources and den sites and reduced hunting and predation, leading to higher densities of raccoons (21,22). Anthropogenic food sources, some inadvertent and others purposefully provided by residents, are important contributing factors to high raccoon densities. Pet food, which is high in protein and fat content, is an important food source for urban and suburban raccoons. In addition, raccoons may forage on fruits and vegetables from gardens and on food wastes from garbage containers (22). Numerous potential den sites are found in urban areas, including ground-based decks, crawl spaces under homes, outbuildings, culvert pipes, and chimneys. In the Monterey Peninsula cities (Pacific Grove and Carmel), we observed that mature Monterey pines (Pinus radiata) were commonly used as daytime resting sites by urban raccoons.

In rural environments and wooded parks, raccoons tend to prefer raised horizontal surfaces, such as logs, stumps, limbs, and forks of trees as latrine sites (1,2,12). Our results show that accessible roofs of houses and sheds are also common locations for latrines in urban/suburban areas. Many roof latrines in Pacific Grove and Carmel were apparently used for years without the homeowner’s knowledge. These often accumulated substantial amounts of feces. During periods of rainfall, this fecal matter washes down rain gutters to the ground near residences, thus becoming more accessible to family members. Such ground contamination from roof top latrines has been implicated in a recent case of B. procyonis neural larva migrans in an 11-month-old child at a day-care facility in Santa Barbara, California (D. Paul, et al., unpub. data).

Ground latrines, which were especially common in San Jose, are also important foci of B. procyonis eggs due to their accessibility. Young children (1–4 years of age) frequently have pica or geophagia and often put objects found on the ground in their mouth. They are especially at risk of accidentally ingesting B. procyonis eggs and account for most cases of severe infection (2,3). Moreover, feces on the ground decompose into the surrounding soil, leaving no sign of their presence, but infective eggs released from the feces may remain viable for years (1,2).

In the late 1990s, both Pacific Grove and Carmel had ongoing raccoon problems, as judged by frequent complaints from citizens. In Pacific Grove, this situation prompted (since 1998) an ongoing program to trap and euthanize nuisance raccoons. Pacific Grove and Carmel have also increased their educational efforts aimed at reducing anthropogenic food sources and shelter for raccoons. Carmel has had no such programs, which may be the reason for the difference in latrine densities between these two cities. The study area in San Jose had few complaints, yet the mean number of latrines per property and the mean density of latrine sites was similar to Pacific Grove and Carmel. The major difference was in the distribution of latrines; San Jose had a greater percentage of properties without latrines, compared with the other two cities, suggesting differences in raccoon density and property usage in this community.

B. procyonis can produce devastating neurologic disease in humans, especially young children (2–11). B. procyonis is much more virulent than the dog roundworm, T. canis, the most frequently encountered cause of larva migrans in humans (3). Clinical signs of CNS infection with B. procyonis may develop as soon as 2–4 weeks after ingestion of infective eggs (23). Factors influencing the severity of CNS disease in humans and other animals include the number of eggs ingested, the extent and pattern of larval migration in the tissues, especially the CNS, the severity of inflammation caused by migrating larvae, and the amount of tissue necrosis.

Symptoms of baylisascariasis range from varying degrees of mild CNS dysfunction, to severe neural deficits with paralysis, coma, blindness, and death (2–11,23). The larvae of B. procyonis have a noted tendency to invade the brain, causing neural larva migrans and ocular larva migrans. Clinical neural or ocular larva migrans is an accidental consequence of somatic migration and larval distribution. Experimental infections in animals have shown that 5%-7% of larvae enter the CNS, but the damage they cause is extensive, attributable primarily to their large size and aggressive migration (1–3,23). Obviously, the greater the number of B. procyonis eggs ingested, the more severe the potential clinical problems.

Ingestion of large numbers of B. procyonis eggs may produce rapidly fatal neural larva migrans. Despite treatment, progressive neurologic deterioration often continues because of the severe CNS damage and inflammation (2,3,23). Those who survive often have profound neurologic impairment and are severely incapacitated. Their condition may progressively worsen as the brain undergoes postinflammatory atrophy (3,7,23). Diagnosis is often delayed because B. procyonis infection is generally not considered during early patient evaluation. This delay contributes to the severity of disease because the larvae continue to migrate unimpeded in CNS tissues, making the prognosis poorer despite later treatment. This infection should be strongly considered in any patient, particularly a young child who has eosinophilic encephalitis, peripheral eosinophilia, and a history of possible exposure. Albendazole and steroids should be administered immediately while serologic and other confirmation of B. procyonis infection are sought (2,3,7–11).

Human exposure to B. procyonis eggs must be prevented, especially in urban and suburban areas where humans and raccoons coexist. Children should be watched carefully when playing in areas with known populations of raccoons and latrines (3). If children are seen to ingest raccoon feces from a latrine or other area, albendazole should be administered immediately (25–50 mg/kg/d x 10d; or 400 mg twice a day x 10d), and the raccoon feces sent for examination for B. procyonis eggs (3). Children should be taught to avoid fecal material, especially from raccoon latrines, and to thoroughly wash their hands after playing outdoors (3). Property owners are advised to inspect their properties and homes periodically, including roofs, for latrines.

If latrines are found, determining what is attracting raccoons to the location is important. Raccoons are readily attracted to sources of food, water, and shelter. Misguided persons who actively feed raccoons or leave pet food outdoors may contribute greatly to problems for other property owners in an area. Advice can usually be sought from local animal control or wildlife management agencies to determine what is attracting raccoons to the area and how to take measures to exclude them from taking up residence or establishing latrines in a particular location.

Latrines should be removed promptly and fecal material disposed of properly (2,3). Wearing rubber gloves, protective overalls, and rubber boots will reduce the possibility of exposure through self-contamination during cleanup activities. If one is working in a confined space such as an attic, a particle facemask should be worn to reduce the possibility of exposure to fungal spores or other contaminants. Feces should be carefully removed, double-bagged in plastic garbage bags, then placed in routine garbage containers for disposal in a landfill or by incineration. If the latrine is located on the ground, approximately 5–7.5 cm of underlying soil should also be removed and discarded.

B. procyonis eggs are difficult to destroy without resorting to high heat (e.g., propane gun flame, boiling water, steam) (2). (Obviously, using flame sources around a home is hazardous and should be discouraged unless surfaces like concrete or soil are to be decontaminated.) Furthermore, the eggs have a sticky proteinaceous coat that allows them to adhere to surfaces. They can be rendered less sticky by applications of hot water and bleach, which may be useful for removing residual eggs from flammable surfaces. Additional information regarding latrine removal and decontamination can be found elsewhere (2), or by contacting appropriate government agencies. Further studies are needed concerning the survivability of B. procyonis eggs under varying conditions and the assessment of optimal, situation-specific methods for inactivation.

In areas where raccoon density is high, trapping and removing raccoons may be necessary to decrease depredation and the accumulation of B. procyonis eggs in the environment. Municipalities should educate the public about this parasite and the negative effects of providing food and shelter to raccoons and other wildlife. Reducing the availability of anthropogenic food sources is important to decrease populations of raccoons in urban and suburban environments. Coordinated, comprehensive wildlife management practices are recommended. Given the potential for human exposure to this parasite and considering the risk for very young children, the public should be encouraged to adopt practices that will reduce the possibility of infection by B. procyonis.