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The introduced black rat, Rattus rattus, occurs throughout the native range of the raccoon roundworm, Baylisascaris procyonis, and might incorporate into its life cycle if rats consume parasite eggs, acquire viable infections, and are eaten by raccoons. Although rats forage at raccoon latrines, their role in B. procyonis transmission remains unknown. Here I tested the potential for rats to amplify B. procyonis transmission in California by surveying wild rodents for B. procyonis and conducting scavenger trials with the use of motion-activated cameras. Rattus rattus were infected with B. procyonis at intensities more than 100 times greater than that of co-occurring native Reithrodontomys megalotis and Peromyscus maniculatus. Rodent carcasses were scavenged by opossums, skunks, and raccoons, suggesting that these rodents, particularly R. rattus, contribute to B. procyonis transmission in this coastal California ecosystem.

Baylisascaris procyonis is a nematode whose definitive host is the raccoon ( Procyon lotor ). Adult parasites are not particularly pathogenic to raccoons; however, larvae in intermediate hosts can cause visceral, ocular, and neural larva migrans. Humans serve as dead-end hosts, and pathological responses are similar to those found in infected intermediate hosts. Infected raccoons expose intermediate hosts through their feces, which can contain millions of B. procyonis eggs. Our objective was to determine how the quantity and viability of B. procyonis eggs in soil changed over time within different soil texture, moisture, and sun exposure. To examine egg survival and movement through soil we placed 100 B. procyonis eggs on 100 squares in 48 boxes representing a full factorial treatment of soil texture, moisture, and sun level. We monitored egg percolation and survival for 2 yr, removing (at 0, 1, 3, 6, 12, 18, and 24 mo) 5 squares from each box and counting the number of viable eggs at each depth in the soil column. Dry soils were mainly impermeable; even after 2 yr, >60% of B. procyonis eggs remained on the surface of all soil textures. Wet soils were more permeable than dry soils, but even in wet sandy soils where the greatest egg movement occurred, it required 1 yr before 60% of eggs transitioned from the soil surface to the next soil depth. For all soil textures, moistures, sun exposures, and depths, >92% of B. procyonis eggs remained viable after 2 yr in the southern Texas environment. Therefore, high exposure risk exists for potential hosts because B. procyonis eggs remain viable on or near the soil surface for at least 2 yr.

There is a growing body of evidence that habitat fragmentation resulting from anthropogenic land use can alter the transmission dynamics of infectious disease. Baylisascaris procyonis , a parasitic roundworm with the ability to cause fatal central nervous system disease in many mammals, including humans, is a zoonotic threat, and research suggests that parasite recruitment rates by intermediate hosts are highly variable among forest patches in fragmented landscapes. During 2008, we sampled 353 white-footed mice ( Peromyscus leucopus ) from 22 forest patches distributed throughout a fragmented agricultural ecosystem to determine the influence of landscape-level habitat attributes on infection rates of B. procyonis in mice. We characterized each mouse in terms of infection status and intensity of infection, and calculated (on a patch-wide basis) prevalence, mean abundance of B. procyonis , and mean intensity of infection. We used an information-theoretic approach to develop a suite of candidate models characterizing the influence of landscape attributes on each of our measured characteristics of B. procyonis infection in white-footed mice, based on previous knowledge of raccoon ( Procyon lotor ) ecology and B. procyonis distribution in agricultural ecosystems. We observed evidence of B. procyonis infection in mice across all 22 habitat patches sampled. However, parasite recruitment rates and intensity were highly variable among patches, and the results of our analyses suggest that spatial variability in B. procyonis infections was primarily driven by emergent properties of fragmented ecosystems. In particular, prevalence, abundance, and intensity of B. procyonis infections in mice were negatively associated with the size and connectivity of forest patches. These results support previous studies indicating that habitat fragmentation can alter the transmission dynamics of infectious disease, and suggest that factors below the scale of landscape, i.e., fine-scale habitat structure or demographic and behavioral attributes of intermediate and/or definitive hosts, also may be important for predicting patterns of B. procyonis infection in intermediate hosts.

Infective stages of helminths of 5 species that occur as adults in marine mammals were found in burbot, Lota lota (L.) (Gadidae), from the lower Kuskokwim River (southwestern Alaska): Diphyllobothrium alascense Rausch et Williamson, 1958; Pyramicocephalus phocarum (Fabricius, 1780); Corynosoma strumosum (Rudolphi, 1801); Corynosoma semerme (Forsell, 1904); and Pseudoterranova decipiens (Krabbe, 1878). Some larval stages were obtained also from smelt, Osmerus mordax dentex Steindachner, an anadromous fish important as prey of burbot. Burbot, which are freshwater fish, could become paratenic hosts of those helminths by means of at least 3 interactions: by consuming marine fishes in brackish waters at river mouths, by feeding on marine fishes that enter lower reaches of rivers, or by preying on anadromous fishes as they migrate up rivers. Consumption of burbot by people may result in infection by helminths of marine origin; of those recorded, only P. decipiens may be significantly pathogenic. Attempts to rear P. phocarum in dogs were unsuccessful. Plerocercoids of D. alascense, of very small size and found only in the gastric lumen of burbot, readily infected dogs. For study of their development, strobilae were obtained at intervals of 48 hr to 32 days postinfection. In heavy infections, some strobilae developed slowly, while others underwent rapid development.

Settling rates and densities of small bodies can be determined by recording settling rates in fluids of different densities, but similar viscosities, and applying Stoke's law. However, at low Reynolds numbers, drag effects reduce the object's settling rate and must be accounted for in sedimentation experiments. Using a revised protocol for spores of the myxozoan Henneguya doori that accounted for significant drag effects exerted by the experimental apparatus, we improve upon a previously described technique and apply it to eggs of the sealworm, Pseudoterranova decipiens. Sealworm eggs have a density of 1.08 x 10(3) kg/m3 and a characteristic Reynolds number of 6 x 10(-3). Fixed eggs settle in seawater at rate of 1.09 x 10(-4) m/sec, whereas fresh eggs settle at a rate of 1.01 x 10(-4) m/sec. Given reported current speeds on the Scotian Shelf off Nova Scotia, Canada, eggs would be transported approximately 50 km in 100 m of water in 12 days before sedimenting on the bottom. Eggs passed 1 m from the bottom would take about 3 hr to settle, and be transported 0.5 km. The size and density of sealworm eggs, and thus their resulting sedimentation rate, may have adaptive value in that they prevent excessive dispersion in space by strong oceanic currents.

A single third-stage larva of the fish nematode Raphidascaris acus (Bloch, 1779) (body length 1.77 mm) was found in 1 of 775 gammarids Gammarus fossarum Koch examined from the Jihlava River, Czech Republic. This is the first confirmed record of the advanced L, of this species from an invertebrate host, showing that an invertebrate may serve as true intermediate host of this nematode, in addition to lower aquatic vertebrates. Until now, invertebrates have generally been considered as paratenic hosts of the second-stage larvae of R. acus.