Can we predict the success of a parasite to colonise an invasive host?

To understand whether a parasite can exploit a novel invasive host species, we measured reproductive performance (number of eggs per female per day, egg size, development rate and size of new imagoes) of fleas from the Negev desert in Israel (two host generalists, Synosternus cleopatrae and Xenopsylla ramesis, and a host specialist, Parapulex chephrenis) when they exploited either a local murid host (Gerbillus andersoni, Meriones crassus and Acomys cahirinus) or two alien hosts (North American heteromyids, Chaetodipus penicillatus and Dipodomys merriami). We asked whether (1) reproductive performance of a flea differs between an alien and a characteristic hosts and (2) this difference is greater in a host specialist than in host generalists. The three fleas performed poorly on alien hosts as compared to local hosts, but the pattern of performance differed both among fleas and within fleas between alien hosts. The response to alien hosts did not depend on the degree of host specificity of a flea. We conclude that successful parasite colonisation of an invasive host is determined by some physiological, immunological and/or behavioural compatibility between a host and a parasite. This compatibility is unique for each host-parasite association, so that the success of a parasite to colonise an invasive host is unpredictable.

Nematofauna of Rodents of the Families Heteromyidae and Cricetidae from the Mexican Plateau.

As a part of an ongoing project to inventory the helminth parasites of rodents in Mexico, 85 specimens of 2 families of rodents were collected from the Mexican Plateau: Cricetidae ( Neotoma sp., Neotoma leucodon , Onychomys arenicola , Peromyscus sp., Peromyscus eremicus , and Reithrodontomys sp.) and Heteromyidae ( Chaetodipus sp., Chaetodipus eremicus , Chaetodipus hispidus , Dipodomys merriami , Dipodomys ordii , Dipodomys ornatus, Dipodomys spectabilis , Liomys irroratus , Perognathus sp., and Perognathus flavus ). A total of 13 taxa of helminths were found: Heteromyoxyuris longejector, Heteromyoxyuris otomii, Heteromyoxyuris sp., Onchocercidae gen. sp. 1 and sp. 2, Physalopteridae gen. sp., Protospirura dipodomis, Pterygodermatites dipodomis, Subulura sp., Syphacia sp., Trichuris dipodomis, Vexillata liomyos, and Vexillata armande. The highest species richness was recorded in D. merriami (7 taxa). This study is the first report of nematodes from O. arenicola (Physalopteridae gen. sp.) and C. eremicus (H. longejector) and for V. liomyos from D. merriami . All reports of these species of nematodes represent new collection localities in Mexico.

Effect of prescribed fire for tick control in California chaparral.

Prescribed fire was investigated as a method for controlling ixodid and argasid ticks in chaparral habitats in northern California. Two experimental and two adjacent control plots within a wildlife preserve were monitored for 1 yr postburn. Ticks were collected by flagging vegetation, by CO2-baited pitfall trap, and by live-trapping rodents. Twice as many rodents were caught at control sites compared with burn sites and no dusky-footed woodrats, Neotoma fuscipes Baird, were found in the treatment sites postburn. This species is known to be a reservoir of the agents of Lyme disease, Borrelia burgdorferi sensu stricto Johnson, Schmid, Hyde, Steigerwalt & Brenner, and human granulocytic anaplasmosis, Anaplasma phagocytophilum Dumler, Barbet, Bekker, Dasch, Palmer, Ray, Rikihisa, Rurangirwa. Six ixodid tick species were removed from rodents (Ixodes pacificus Cooley & Kohls, Ixodes jellisoni Cooley & Kohls, Ixodes spinipalpis Hadwen & Nuttall, Ixodes woodi Bishopp, Dermacentor occidentalis Marx, and Dermacentor parumapertus Neumann), two of which transmit bacterial zoonotic agents to people in the far-western United States. There was no decrease in number of ticks per animal trapped at either burn site compared with controls; in fact, the mean number of immature I. pacificus per rodent was significantly higher at one burn site than its control site. Soil refugia may protect ticks from fire-induced mortality; the argasid tick Ornithodoros coriaceus Koch, which lives in soil, was unaffected by the prescribed fire as were I. pacificus and D. occidentalis buried in packets 2.5 cm below ground. We conclude that although prescribed fires in chaparral habitats may diminish local rodent abundance, it does not decrease tick loads on rodents. Furthermore, burning chaparral does not result in a decreased abundance of adult ixodid ticks on vegetation and apparently does not affect argasid or ixodid ticks that are sheltered within soil refugia.

Feeding preferences of the immature stages of three western north American ixodid ticks (Acari) for avian, reptilian, or rodent hosts.

Larval and nymphal Ixodes pacificus Cooley and Kohls, I. (Ixodes) jellisoni Cooley and Kohls, and Dermacentor occidentalis Marx were tested for host preference when simultaneously presented with a deer mouse (Peromyscus maniculatus Wagner), California kangaroo rat (Dipodomys californicus Merriam), western fence lizard (Sceloporus occidentalis Baird and Girard), and California towhee (Pipilo crissalis Vigors) in an experimental apparatus. Differences were observed in the preferences among the three species and between life stages. More larvae of all species approached and contacted hosts than did nymphs. Subadult I. pacificus entered all host-containing chambers in the highest numbers and remained on lizards most often after contact. Subadult I. jellisoni entered and remained in the chambers containing kangaroo rats, while rejecting mice, lizards, and birds as hosts. Subadult D. occidentalis most frequently entered rodent-containing chambers and contacted these hosts. After overnight exposure to all nonavian hosts, only I. pacificus parasitized and fed successfully on all three animals. I. jellisoni fed only on kangaroo rats and D. occidentalis fed only on rodents. Molting success ranged from approximately 66 to 95% among tick species and stages. We concluded that, under laboratory conditions, I. pacificus larvae and nymphs prefer western fence lizards, but also will parasitize rodents. Dermacentor occidentalis immatures use deer mice and kangaroo rats similarly, whereas I. jellisoni subadults exclusively parasitize kangaroo rats. California towhees are considerably less attractive as hosts for these three ticks. These host preferences are consistent with what is known about the natural feeding habits of all three ticks.

Sylvatic maintenance of Borrelia burgdorferi (Spirochaetales) in Northern California: untangling the web of transmission.

Lyme borreliosis is associated with several genospecies of Borrelia burgdorferi sensu lato (s.l.) (Spirochaetales), but human disease has been associated only with Borrelia burgdorferi sensu stricto (s.s.) Johnson, Schmid, Hyde, Steigerwalt & Brenner in the western United States. Restriction fragment length polymorphism (RFLP) analysis of rrf-rrl amplicons from 124 tick and mammalian isolates from various habitats yielded 13 RFLP patterns. Of these patterns, six were patterns previously associated either with Borrelia bissettii Postic, Marti Ras, Lane, Hendson & Baranton or Borrelia burgdorferi s.s., and the remaining seven patterns belonged to diverse and previously uncharacterized Borrelia spp. Uncharacterized Borrelia spp. were cultured most frequently from Ixodes spinipalpis Hadwen & Nuttall and California kangaroo rats, Dipodomys californicus Merriam, inhabiting grasslands, and B. bissettii from I. spinipalpis and dusky-footed woodrats, Neotoma fuscipes Baird, associated with oak woodlands or chaparral. B. burgdorferi s.s. typically was isolated from host-seeking Ixodes pacificus Cooley & Kohls collected in dense oak woodlands, woodland-grass, or redwood forests. Although some isolates of B. burgdorferi s.s. were cultured from woodrats, there was no clear association of this human pathogen with any vertebrate host. These findings, along with recent evidence indicating that the western gray squirrel, Sciurus griseus Ord, may be an important reservoir of B. burgdorferi s.s. in Californian oak woodlands, suggest that our earlier hypothesis implicating an enzootic cycle involving woodrats and I. spinipalpis is insufficient to account for observed patterns of infection in nature.

Biotic and abiotic effects on endoparasites infecting Dipodomys and Perognathus species.

Between 1989 and 1998, 3,504 rodents of the genera Dipodomys and Perognathus were collected from 4 permanent collecting sites on the University of New Mexico's Long Term Ecological Research station, located on the Sevilleta National Wildlife Refuge (SNWR), Socorro County. New Mexico. All animals were killed and examined for endoparasites (acanthocephalans, cestodes, coccidia, and nematodes). The present report focuses on 3 endoparasite groups, cestodes, coccidia, and nematodes. Specific analyses address how prevalence changes were related to abiotic factors such as habitat, season, or precipitation, and how prevalence of each parasite species in each host species differed in relation to host age, host sex, host reproductive status, host body mass, host density, parasite-parasite interactions, and host specificity. A logistic regression was used to determine which host characters and which abiotic factors are correlated with a parasite infection. Significant variables for at least half of the parasites include season, site, and winter precipitation. However, no parasite prevalences were correlated, and significant variables were not identical between parasites, indicating that each parasite species varied independently and that no generalizations can be drawn. The parasite prevalences in these rodents on the SNWR vary in independent and complex ways.

Botfly (Diptera:Oestridae) parasitism of Ord's kangaroo rats (Dipodomys ordii) at Suffield National Wildlife Area, Alberta, Canada.

During field study of Ord's kangaroo rat (Dipodomys ordii) at Suffield National Wildlife Area, Alberta, Canada, a high prevalence of parasitism by botfly (Diptera: Oestridae) larvae was observed. Botflies have not previously been documented as parasites of kangaroo rats. Botfly parasitism could have a significant impact on the growth, survival, and reproduction of Ord's kangaroo rat, which is considered a vulnerable species in Canada. Therefore, it is important to investigate how botfly parasitism varies with season and with gender or age of host. In 1995, 525 individual kangaroo rats were caught by nightlighting and live trapping for a total of 952 capture records. Upon capture, each kangaroo rat was ear-tagged and thoroughly examined for parasites and wounds. Third-instar botfly (Cuterebra polita) larvae were observed in kangaroo rats between 16 June and 23 August. Prevalence was 34% based on 454 kangaroo rats sampled during that time, whereas the mean intensity was 2.3 larvae per infested host (n = 156, range = 1-11). In contrast to some other studies of botfly parasitism of rodents, there were no gender or age biases in either prevalence or intensity of infestation. The index of dispersion was 2.8, indicating that the parasites were aggregated in hosts. Botfly parasitism could be an important factor affecting northern populations of kangaroo rats; future investigations into the potential effects of botfly larvae on host fitness are warranted.

Fleas (Siphonaptera) infesting giant kangaroo rats (Dipodomys ingens) on the Elkhorn and Carrizo Plains, San Luis Obispo County, California.

The giant kangaroo rat, Dipodomys ingens (Merriam), has a limited distribution in the San Joaquin Valley, CA. Because of reductions in its geographic range, largely resulting from humans, the species was listed as an endangered species in 1980 by the California Fish and Game Commission. As part of a study of the community ecology of southern California endangered species, including D. ingens, we were able to make flea collections from the rats when they were trapped and marked for population studies. All but one of the fleas collected from the D. ingens in this study were Hoplopsyllus anomalus, a flea normally associated with ground squirrels (Sciuridae). It has been suggested that giant kangaroo rats fill the ground squirrel niche within their range. Our data indicate that this role includes a normal association with Hoplopsyllus anomalus.

Lyme disease in California: a novel enzootic transmission cycle of Borrelia burgdorferi.

Knowledge of zoonotic transmission cycles is essential for the development of effective strategies for disease prevention. The enzootiology of Lyme disease in California differs fundamentally from that reported from the eastern United States. Woodrats, not mice, serve as reservoir hosts, and Ixodes neotomae, a nonhuman-biting tick, maintains the agent of Lyme disease, Borrelia burgdorferi, in enzootic cycles. The western black-legged tick, Ixodes pacificus, is the primary vector to humans, but it appears to be an inefficient maintenance vector. Isolates of B. burgdorferi from California exhibit considerable antigenic heterogeneity, and some isolates differ strikingly from isolates recovered from this and other geographic regions.

Parasitic and phoretic arthropods of the elephant-eared and the Santa Cruz kangaroo rats.

The parasitic and phoretic arthropods of the elephant-eared kangaroo rat (Dipodomys elephantinus) and Santa Cruz kangaroo rat (D. venustus) are reported; most of these represent new host records. Thirteen of 14 (93%) of D. elephantinus and 11 of 12 (92%) of D. venustus had 11 and nine arthropod species, respectively. Larval and nymphal stages of the tick Dermacentor occidentalis were the most prevalent parasite (77%) on D. elephantinus whereas the mesostigmatid mite Androlaelaps fahrenholzi was the most prevalent (56%) on D. venustus. The arthropod fauna of these two closely related rodents were similar with seven of the 14 arthropod species occurring on both host species. Two species of the host specific listrophorid mite of the genus Geomylichus were found on both hosts.

Helminths of sympatric populations of kangaroo rats (Dipodomys ordii) and grasshopper mice (Onychomys leucogaster) from the high plains of eastern New Mexico.

During a 1-yr period 124 Dipodomys ordii and 92 Onychomys leucogaster were trapped from the same locality and were examined for helminths. Only 1 cestode species (Catenotaenia linsdalei) was recovered from D. ordii, whereas O. leucogaster was infected with 2 nematoda (Litomosoides carinii, Mastophorus muris), 2 cestoda (Hymenolepis citelli, and 1 unknown), and 1 acanthocephalan (Moniliformis clarki) species. All represent new host and distribution records.

Eimeria chihuahuaensis sp.n. and other coccidia from Dipodomys spp. in El Paso County, Texas.

Dipodomys merriami Mearns and Dipodomys ordi Woodhouse were surveyed for coccidia in El Paso County, Texas. Infections with Eimeria chobotari, Eimeria dipodomysis and Eimeria balphae were 24.8%, 4.4%, and 11%, respectively, for D. ordi. Dipodomys merriami had an infection level of 23.8% with E. chobotari. Four animals concurrently harbored E. chobotari and E. balphae or E. dipodomysis or a new species Eimeria chihuahuaensis. Male and female host infection levels were not significantly different. The new species is described and photographs of 3 previously described Eimeria from Dipodomys are presented.

The endogenous stages of Eimeria utahensis (Protozoa: Eimeriidae) in the kangaroo rat, Dipodomys ordii.

The endogenous life cycle of Eimeria utahensis is described from experimentally infected kangaroo rats, Dipodomys ordii. The endogenous asexual cycle consisted of 4 generations of meronts. First-generation meronts were concentrated in the anterior third of the small intestine. The succeeding generations of meronts and the sexual stages were concentrated in the middle third of the small intestine. First-generation meronts had a mean diameter of 9.7 micrometer and contained 12 to 16 merozoites. Second-generation meronts had a mean diameter of 8.0 micrometer and contained 12 to 16 merozoites and a residual body. Third-generation meronts had a mean diameter of 12.4 micrometer and contained 4 to 8 merozoites. Fourth-generation meronts had a mean diameter of 8.6 micrometer and contained 16 to 24 merozoites. Young gamonts were located in epithelial cells of the crypts of the small intestine. Shortly after the parasites entered the epithelial cells, the infected cells became displaced into the lamina propria, and most of the mature gamonts were in this location. The nuclei of host cells containing young sexual stages became greatly elongated and flattened. A few young gamonts were seen in cells in which the host cell nuclei were dividing. During development, nuclei of microgamonts became arranged on the periphery of numerous compartments. Only one type of wall-forming body could be distinguished in the macrogamonts.