Unnatural Host Research Articles

Identification and Characterization of H2N3 Avian Influenza Virus from Backyard Poultry and Comparison with Novel H2N3 Swine Influenza Virus

In early 2007, H2N3 influenza virus was isolated from a duck and a chicken in two separate poultry flocks in Ohio. Since the same subtype influenza virus with hemagglutinin (H) and neuraminidase (N) genes of avian lineage was also identified in a swine herd in Missouri in 2006, the objective of this study was to characterize and compare the genetic, antigenic, and biologic properties of the avian and swine isolates. Avian isolates were low pathogenic by in vivo chicken pathogenicity testing. Sequencing and phylogenetic analyses revealed that all genes of the avian isolates were comprised of avian lineages, whereas the swine isolates contained contemporary swine internal gene segments, demonstrating that the avian H2N3 viruses were not directly derived from the swine virus. Sequence comparisons for the H and N genes demonstrated that the avian isolates were similar but not identical to the swine isolates. Accordingly, the avian and swine isolates were also antigenically related as determined by hemagglutination-inhibition (HI) and virus neutralization assays, suggesting that both avian and swine isolates originated from the same group of H2N3 avian influenza viruses. Although serological surveys using the HI assay on poultry flocks and swine herds in Ohio did not reveal further spread of H2 virus from the index flocks, surveillance is important to ensure the virus is not reintroduced to domestic swine or poultry. Contemporary H2N3 avian influenza viruses appear to be easily adaptable to unnatural hosts such as poultry and swine, raising concern regarding the potential for interspecies transmission of avian viruses to humans.

Characterization and Identification of Erysipelothrix rhusiopathiae Isolated from an Unnatural Host, a Cat, with a Clinical Manifestation of Depression

Erysipelothrix rhusiopathiae is pathogenic for humans, many domestic animals and wild birds, but infectious cases with clinical symptoms in cats have not been reported. E. rhusiopathiae was recovered from a 4-month Russian blue breed cat with a very poor body condition score of 1 (BCS: 1/5). The isolate was typed as serotype 2b. Mice experimentally infected with the clinical isolate of E. rhusiopathiae through subcutaneous or intraperitoneal routes survived, and the organism was recovered from the spleen and synovial and pericardial fluids. Cats experimentally inoculated with the isolate either orally or subcutaneously survived but commonly exhibited depression and emaciation together with localized erythemal lesion of the skin accompanied by purulent ocular discharge. On hematological analysis, the number of total white blood cells was high compared with that in normal cats. Histological examination revealed congestion and moderate inflammation with focal necrosis. This observation may provide insight on E. rhusiopathiae infection in cats with the possible epidemiological significance and implications as a potential source of infection to other animals and humans.

Fatal epizootic equine herpesvirus 1 infections in new and unnatural hosts

In a zoological collection, four black bears (Ursus americanus) died from neurological disease within six months. Independently in a geographically different zoo, two Thomson's gazelles (Eudorcas thomsoni) and 18 guinea pigs (Cavia porcellus f. dom.) suffered from neurological disorders. In addition, guinea pigs showed abortions and stillbirths. All affected animals displayed a non suppurative meningoencephalitis with intranuclear inclusion bodies. Immunohistology demonstrated equine herpes virus antigen and ultrastructurally herpes viral particles were detected. Virus isolation and molecular analysis identified neurotropic equine herpesvirus (EHV) 1 strains in both epizootics. There is serological evidence of a possible virus transmission from other equids to the affected animals. Cross-species transmission of EHV-1 should be considered in the management of captive wild equids and ungulates, particularly with respect to fatal disease in irreplaceable species.

The effect of topical ocular corticosteroid administration in dogs with experimentally induced latent canine herpesvirus-1 infection

Recurrent herpes simplex virus-1 (HSV-1) ocular infection is a frequent cause of morbidity and blindness. Factors that trigger viral reactivation are poorly understood and the role of topical ocular corticosteroid administration in the development of recurrent HSV-1 ocular disease is not clear. Clinical reports and epidemiological studies suggested topical corticosteroids may reactivate latent HSV-1 and result in recrudescent ocular disease; however, experimental studies to establish this causal relationship produced inconsistent results. The previous experimental studies were performed by infecting unnatural host species with HSV-1 and aspects of viral behavior and reactivation within these animals may differ from the host for which the virus is adapted. The purpose of the study reported here was to determine if topical ocular corticosteroid administration results in viral reactivation and recrudescent ocular disease in a host-adapted pathogen animal model of HSV-1 recurrent ocular disease. Canine herpesvirus-1 (CHV-1) is a corticosteroid-sensitive alphaherpesvirus that is biologically related to HSV-1 and induces similar ocular lesions in canids during recurrent infection. A randomized, masked, placebo-controlled, crossover study was performed. Primary ocular CHV-1 infection was experimentally induced in mature specific pathogen-free beagles by topical ocular inoculation and the presence of reactivatable latency was later confirmed by administration of an immunosuppressive dosage of systemic corticosteroid to the dogs. Twelve months following experimental CHV-1 reactivation, dogs were administered either topical ocular prednisolone acetate (1.0% ophthalmic suspension, one drop in both eyes, four times daily) or placebo (artificial tear solution, one drop in both eyes, four times daily) for 28 days. After a 14 day washout period, the treatment groups were reversed and study agents administered for an additional 28 days. Ophthalmic examinations, in vivo ocular confocal microscopy, real-time quantitative CHV-1 polymerase chain reaction assays, and CHV-1 serum neutralization antibody titers were performed at regular intervals throughout the study. Viral reactivation was not detected in dogs administered topical ocular prednisolone or placebo as determined by clinical ocular disease recrudescence, in vivo ocular confocal microscopic findings, ocular viral shedding, and serologic response. Similar to other animal models of recurrent HSV-1 ocular infection, the behavior of latent CHV-1 in dogs may differ from HSV-1 in humans; however, results of the present study suggest administration of topical ocular prednisolone at the evaluated drug concentration, dosing frequency, and treatment duration is not likely to result in detectable reactivation of latent CHV-1 in experimentally infected dogs. This may be attributed to insufficient systemic absorption of locally administered corticosteroid to reactivate latent virus and produce recurrent disease. Crystalline corneal opacities that were apparently not associated with viral reactivation were detected by clinical examination and in vivo confocal microscopy in two dogs during topical ocular prednisolone administration. The crystalline keratopathy may have resulted from corneal degeneration associated with metaherpetic disease, corticosteroid administration, or a combination of both factors.

A Case for Innate Immune Effector Mechanisms as Contributors to Disease Resistance in SIV-Infected Sooty Mangabeys

Natural or experimental infection of the African sooty mangabey (SM) with the simian immunodeficiency virus (SIV) results in chronic high levels of virus replication but is associated with none of the debilitating immunopathology, including the marked CD4 T-cell depletion, persistent cell activation and acquired immunodeficiency, that afflicts non-natural hosts such as SIV-infected Asian rhesus macaques (RM) and HIV-infected humans. Although SIV-infected RM have served as important models of AIDS given their remarkably similar course of disease to HIV-infected humans, deciphering the immune mechanisms that enable SIV-infected SM to resist disease development despite high viremia has yet to be defined. Intense studies for the past two decades using these nonhuman primate models have been conducted with the hope that this will yield better insight into the pathogenesis of AIDS, translating into the development of therapeutic strategies for HIV-infected individuals such as but not limited to identifying correlates of protective immunity that can be harnessed for the preparation of effective vaccines. Although much has been reported about SIV-specific adaptive immune responses in both the natural and unnatural hosts of SIV, we submit that innate immunity may play a larger than previously appreciated role in SIV pathogenesis, in particular during the period of acute infection. The purpose of this review is to therefore highlight the recent advances that have been made in understanding innate immune responses in SIV-infected SM and to discuss the role(s) of the major innate immune cell lineages that potentially contribute to disease resistance in this non-human primate species.

Experimental infection of calves with Newcastle disease virus induces systemic and mucosal antibody responses

Calves were infected intranasally and intratracheally with Newcastle disease virus (NDV), an avian paramyxovirus. Clinical signs, viral replication, and antibody production were evaluated. This study showed that NDV replicated in calves, as evidenced by development of NDV-specific humoral and mucosal antibody responses, but was attenuated in this unnatural host. These results suggest that NDV has the potential for development as a host-range-restricted, intranasal vaccine vector for cattle that lack preexisting immunity to NDV.

Comparative Susceptibility of Japanese and European Eels to Infections with Pseudodactylogyrus spp. (Monogenea)

Japanese eel Anguilla japonica and European eel A. anguilla, 65 individuals each, were exposed in a tank to 8,600 oncomiracidia of Pseudodactylogyrus bini and P. anguillae, monogeneans originally recorded on Japanese eel from Asia. Infection was monitored weekly for 6 weeks to compare susceptibility to these monogenean infections between the two eel species. Approximately 40% of the oncomiracidia infected the eels. In the six samplings, both P. bini and P. anguillae were always found in greater numbers on the gills of European eel than on Japanese eel. The first generation of parasites matured within 2 weeks, laying eggs in the tank, and the second generation appeared on the gills of the eels on the third week. European eel was more susceptible not only to the first but also to the second and later generations of parasites than Japanese eel. Besides, both parasites grew faster on European eel than on Japanese eel. This is the first experimental evidence that there are substantial differences in the susceptibility to P. spp. infection between European eel, an unnatural host in Japan, and Japanese eel, the natural host in this country.

A new species of Gonatocerus (Hymenoptera: Mymaridae) from Argentina, an egg parasitoid of Tapajosa rubromarginata (Hemiptera: Cicadellidae)

Specimens of Gonatocerus virlai S. Triapitsyn, Logarzo & de León sp. n., which belongs to the ater species group of Gonatocerus Nees (Mymaridae), were reared in Argentina mostly from wild-collected and sentinel eggs of the sharpshooter Tapajosa rubromarginata (Signoret) (Cicadellidae: Cicadellinae: Proconiini) on citrus and corn plants. The distribution and host associations (both natural and laboratory) of G. virlai are given. Under quarantine laboratory conditions in the USA, it was successfully reared for many generations on an unnatural host, the glassy-winged sharpshooter, Homalodisca vitripennis (Germar).

ASCOGREGARINE PARASITES AS POSSIBLE BIOCONTROL AGENTS OF MOSQUITOES

The seemingly ubiquitous presence of gregarine parasites in numerous mosquito taxa (Table 1; Chen 1999) suggests that consideration of these parasites as biological control agents may be a worthwhile endeavor. However, because most studies prior to 1985 did not demonstrate significant fitness (e.g., mortality, adult size) differences between infected and non-infected mosquitoes, Beier and Craig (1985) deemed in their overview of gregarine parasites of mosquitoes that ‘‘There is no evidence that gregarines can be used to control mosquitoes, and no evidence that gregarines in their natural habitat have a significant negative impact on populations of their normal host.’’ (p 182) However, the authors did suggest that because ‘‘conventional strategies for controlling container-breeding mosquitoes are not effective, the possibility of using gregarines in unnatural mosquito hosts should not be ruled out.’’ A number of additional studies have since been published that have examined the pathogenicity of gregarine parasites both for natural and nonnatural hosts, as well as for hosts reared in stressful vs. non-stressful environments. This paper reviews the outcomes of these studies and addresses whether the prospects of using gregarines as mosquito biological control agents have changed with these recent findings.

Guinea Pig-Adapted Foot-and-Mouth Disease Virus with Altered Receptor Recognition Can Productively Infect a Natural Host

We report that adaptation to infect the guinea pig did not modify the capacity of foot-and-mouth disease virus (FMDV) to kill suckling mice and to cause an acute and transmissible disease in the pig, an important natural host for this pathogen. Adaptive amino acid replacements (I(248)-->T in 2C, Q(44)-->R in 3A, and L(147)-->P in VP1), selected upon serial passages of a type C FMDV isolated from swine (biological clone C-S8c1) in the guinea pig, were maintained after virus multiplication in swine and suckling mice. However, the adaptive replacement L(147)-->P, next to the integrin-binding RGD motif at the GH loop in VP1, abolished growth of the virus in different established cell lines and modified its antigenicity. In contrast, primary bovine thyroid cell cultures could be productively infected by viruses with replacement L(147)-->P, and this infection was inhibited by antibodies to alphavbeta6 and by an FMDV-derived RGD-containing peptide, suggesting that integrin alphavbeta6 may be used as a receptor for these mutants in the animal (porcine, guinea pig, and suckling mice) host. Substitution T(248)-->N in 2C was not detectable in C-S8c1 but was present in a low proportion of the guinea pig-adapted virus. This substitution became rapidly dominant in the viral population after the reintroduction of the guinea pig-adapted virus into pigs. These observations illustrate how the appearance of minority variant viruses in an unnatural host can result in the dominance of these viruses on reinfection of the original host species.

A unified concept of HIV latency

The introduction of highly active antiretroviral therapy (HAART) combining potent drugs that can inhibit reverse transcriptase, integrase and protease activities has changed the natural history of the human immunodeficiency virus (HIV) type 1 disease. Unfortunately, poor penetrability into different anatomic compartments, toxicity and drug resistance are some of the problems related to their prolonged use. The ability of HIV to mutate and become resistant, along with the ongoing viral replication during HAART, can lead to the emergence of independently evolving viral strains in different anatomic compartments (i.e., brain, testes, lymph nodes, etc.). In addition, HAART predominantly effects the viral replication in the activated or differentiating CD+ T lymphocytes, but appears to have a very limited effect on HIV-1 preintegration complexes in the latently infected cells. Existing drug therapies do not eliminate these viral reservoirs, nor do they prevent their formation. New strategies are needed for eliminating protected areas of HIV-1 in vivo. Therefore, the persistence of latent HIV-1 reservoirs is the principal barrier in the complete eradication of HIV-1 infection in patients by antiretroviral therapy at present. African non-human primates (NHPs) naturally infected with various simian immunodeficiency viruses (SIVs) appear not to develop immunodeficiency or AIDS, whereas Asian NHPs, which are unnatural hosts, infected with SIVs, as well humans infected with HIV-1, will nearly always develop progressive loss of CD+ T lymphocytes and a gradual destruction of immune functions. Understanding the difference in the host responses between natural and unnatural hosts, and deciphering which host factors are responsible for the non-pathogenic course of natural SIV infections, would be valuable in developing more-effective treatment or prevention strategies for HIV/AIDS. A number of factors encoded by host cells have been identified that appear to play critical roles in the SIV infection process. Two of these factors, TRIM5α (a member of a large family of proteins known as the TRIM proteins) and cellular apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like-3G (APOBEC3G) have been recently identified. APOBEC3G genes belong to a family of primate genes that produce enzymes (in this case, APOBEC3G) that ‘edit’ RNA by replacing cytosine with guanine into viral particles as the virus undergoes reverse transcription in the cytoplasm of the host cell. HIV-1, in turn, counters with a protein called viral infectivity factor (Vif), which binds to the APOBEC3G enzyme that degrades it. Several other blocking factors have been described, including lentiviral blocking factor (Lv)1 and 2. These factors appear to block the infection at a postentry step; after reverse transcription has occurred, but before proviral integration. Thus, it is crucial to understand the molecular mechanisms involved in the establishment, maintenance and reactivation of lentiviral latency. This review presents various models of HIV-1 latency and forward a new unified model of lentiviral latency.

Koch and His Postulates

As a recipient of the Robert Koch Prize from the German government for my research on cholera, I feel compelled to correct some of the inaccuracies in the D. J. Grimes article “Koch's Postulates—Then and Now,” which appeared in the May 2006 issue of Microbe, p. 223–228. Regardless of who was completely responsible for the precise wording of Koch's Postulates that we know, revere, and practice as much as possible still today, they did emerge from his school. My major issue is with Grimes' not acknowledging that the third postulate with regard to cholera was indeed established by Koch's producing the disease in healthy animals and reisolating the organism from the diseased animals. Although Brock did not discuss this in detail in his otherwise comprehensive book, Robert Koch: a Life in Medicine and Bacteriology, (cited by Grimes), it is noted (p. 182) that “treated animals (bile duct ligation and intra-duodenal inoculation) died in 1.5–3 days following the introduction of less than one-hundredth of a drop of pure culture.” Koch, as described and documented in my review [“Cholera enterotoxin (choleragen): a historical perspective,” (p. 155–187 in D. Barua and W. B. Greenough III, ed., Cholera, Plenum Medical Book Company, New York, 1992], also demonstrated the bactericidal and protective effect of gastric acid (which could be neutralized by carbonate of so-da—a phenomenon to be “rediscovered” by the Maryland Group when they tried to infect American volunteers) as well as the protective effect of peristaltic movement (which could be inhibited by tincture of opium, thus allowing the comma-bacilli to remain longer and gain a foothold in an unnatural host). The ligated rabbit ileal loop model, which Grimes used to revive “somnicells” of Escherichia coli H10407 which had been exposed to seawater, was to come later.

Molecular and biological characteristics of H5 and H7 avian influenza viruses in live-bird markets of the northeastern United States, 1994-2001.

Surveillance for H5 and H7 subtypes of avian influenza virus (AIV) in the live-bird markets (LBMs) of the northeastern United States has been in effect since 1986 when the markets were first recognized as a potential reservoir for AIV. Long-term maintenance of AIV in the LBM system has been documented. However, little is known about the influence of successive cycles of replication in unnatural avian hosts (gallinaceous birds) on the genetics of the virus, especially in the region of the hemagglutinin (HA) gene that can influence pathogenicity. Isolation of low-pathogenicity H5 AIVs from the LBMs has been sporadic; however, in 1994 a low-pathogenicity H7N2 virus was isolated that has persisted in the LBMs for more than 7 yr. Efforts to eliminate the H7 virus from the markets have been unsuccessful. During the 7-yr period, several molecular changes have occurred at the hemagglutinin cleavage site of the H7 virus. These changes include substitutions of proline for threonine and lysine for asparagine, respectively, at the -2 and -5 positions of the HA1 protein. In addition, there has been a 24 nucleotide base-pair deletion in the receptor binding region of the HA1. The accumulation of an additional basic amino acid at the cleavage site is a cause for concern to regulatory authorities, and, therefore, efforts to eliminate the virus from the LBM system have been intensified.

Cyclophilin A modulates the sensitivity of HIV-1 to host restriction factors.

Many mammalian species express restriction factors that confer host resistance to retroviral infection. Here we show that HIV-1 sensitivity to restriction factors is modulated by cyclophilin A (CypA), a host cell protein that binds the HIV-1 capsid protein (CA). In certain nonhuman primate cells, the CA-CypA interaction is essential for restriction: HIV-1 infectivity is increased >100-fold by cyclosporin A (CsA), a competitive inhibitor of the interaction, or by an HIV-1 CA mutation that disrupts CypA binding. Conversely, disruption of CA-CypA interaction in human cells reveals that CypA protects HIV-1 from the Ref-1 restriction factor. These findings suggest that HIV-1 has co-opted a host cell protein to counteract restriction factors expressed by human cells and that this adaptation can confer sensitivity to restriction in unnatural hosts. Manipulation of HIV-1 CA recognition by restriction factors promises to advance animal models and new therapeutic strategies for HIV-1 and AIDS.

Trichostome ciliates from Australian marsupials. IV. Distribution of the ciliate fauna

Trichostome ciliates are associated with many different lineages of herbivorous mammals but there are few comparative studies of these associations in each lineage of herbivores. Here the occurrence of the ciliate fauna in a range of herbivorous marsupials (diprotodonts) is investigated and compared with that of ruminants. A total of 371 potential host animals, representing 33 species and 7 families, were examined for the presence of ciliates. The prevalence of endocommensal ciliates within individual host species varied between 0 and 100%. Of the different dietary groups of marsupials examined, only foregut (macropodids) and hindgut (vombatids) fermentative herbivores were found to harbour ciliates; carnivorous (dasyurids), omnivorous (peramelids) and midgut fermenting herbivores (phalangeroids) all lacked ciliates. The majority of ciliate species were oioxenic, several occurred in closely related hosts and some were able to colonise unnatural hosts in captive populations. Ciliate prevalences were found to vary at all levels: between hosts of different species, between conspecific hosts collected at different localities or seasons and between conspecific hosts at one collecting locality. The faunal composition of the 2 marsupial families which harboured ciliates differed greatly: the vombatid fauna was composed exclusively of amylovoracids whereas the macropodids harboured amylovoracids, polycostids and macropodiniids. In comparison to the ciliate fauna of ruminants, the fauna of macropodids is both depauperate and much more host specific. Low species richness in each host may be due to the large numbers of stomach nematodes in macropodids which compete with and may prey upon the ciliates within the stomach. The high levels of host specificity are probably due to different patterns of ciliate transmission in macropodids as they do not ruminate, eructate or feed indiscriminantly on pasture contaminated with saliva containing ciliates.

Biology of <I>Catolaccus hunteri</I> (Hymenoptera: Pteromalidae), A Parasitoid of Pepper Weevil and Boll Weevil (Coleoptera: Curculionidae)

A general description of the life stages and population parameters of Catolaccus hunteri Crawford, a primary ectoparasitoid of pepper weevil, Anthonomus eugenii Cano, and boll weevil, Anthonomus grandis grandis Boheman, is presented. The parasitoids were reared on the unnatural host Callosobruchus maculatus F. The developmental time of C. hunteri at 27 ± 1°C was shorter in males than females. Males completed development in 11.46 ± 0.46 d from egg to adult emergence. Developmental time in females required 13.18 ± 0.81 d from egg to adult at the same temperature. A C. hunteri female (n = 20) laid 466.35 ± 280.39 eggs, of which just 18.35% reached the adult stage; this could be the result of cannibalistic larval behavior combined with high superparasitism observed under laboratory conditions. Female mean longevity was 47.20 ± 12.76 d. The net reproductive rate (Ro), the generation time (G), and the daily intrinsic rate of increase (rm) were 42.713, 33.842, and 0.111, respectively. The fecundity of pepper weevil and boll weevil is discussed.

Purification, Cloning, and Expression of a Novel Salivary Anticomplement Protein from the Tick, Ixodes scapularis

The alternative pathway of complement is an important defense against pathogens and in tick rejection reactions. The tick Ixodes scapularis is able to feed repeatedly on its natural host and has a salivary anticomplement activity that presumably facilitates feeding. In this study, we purified and then obtained the amino-terminal sequence of the I. scapularis salivary anticomplement (Isac). We found a full-length clone coding for Isac by random screening of a salivary gland cDNA library. Expressing Isac cDNA in COS cells reproduced the activity found in tick saliva, namely, inhibition of rabbit erythrocyte lysis by human serum in the presence of Mg(2+) and EGTA, inhibition of C3b binding to agarose in the presence of Mg(2+) and EGTA, and acceleration of factor Bb uncoupling from the C3 convertase generated by the alternative pathway. Recombinant Isac had no effect on the recalcification time of human platelet-poor plasma or in the classical complement pathway, indicating that it is a specific inhibitor similar to the regulators of complement activation of the alternative pathway such as factor H. Isac, however, has no similarity to any protein in the GenBank(TM) data base, indicating that it is a novel and relatively small (18.5 kDa) anticomplement molecule.

Parasitoids and biocontrol of Russian wheat aphid,Diuraphis noxia(Kurdj.) expanding in central Europe

Hymenopterous parasitoids found on the Russian wheat aphid (RWA),Diuraphis noxia(Kurdj.) since the aphid was detected in the Czech Republic in 1995 have been studied. Parasitoids were obtained from aphid samples taken in small grains and from field exposures of banker‐units containing laboratory mass‐reared RWA. The parasitoid species are listed. Their presence on RWA was verified and their host species alternation was also tested in the laboratory. Evidence on some species was obtained only through unnatural host propagation.Aphidius colemaniVier. (a Chilean strain) was purposely introduced, released and became established; its host range, which included both target and non‐target species, is listed. Prediction versus determination of RWA parasitoid complex in central Europe are discussed and the field samples and the exposure trials are compared. The RWA presence in relation to biodiversity in the small‐grains agroecosystem is analysed. An overall parasitoid spectrum of RWA in the Old World (and the world background) is reviewed in relation to the RWA native range and the distribution (expansion) range, respectively. A corresponding analysis of the central European situation, derived from the expansion route of RWA to the Mediterranean, is presented.

Severe reaction in domestic animals following the bite of Ixodes muris (Acari: Ixodidae).

Free tick identification has been offered by our laboratory since 1989, during which time > 8,000 specimens have been submitted. We have noted that the bite of 1 of the less frequently identified ticks, Ixodes muris Bishopp & Smith, may be associated with a severe reaction in domestic animals characterized by extreme pain and swelling at the site and, with more complete engorgement, lethargy, anorexia, and high fever. These symptoms may be confused with other serious illness if the tick is not found. This reaction has not been seen following the bite of other species of ixodid ticks in Maine. Here we report 43 such cases, most involving dogs and cats from which ticks were removed by veterinarians and submitted to our laboratory for identification. Although I. muris was initially widespread in the United States and eastern Canada, its current range is unclear. In view of the potential for severe reaction to the bite of I. muris, the current distribution of the tick needs better definition, as does the mechanism of this response in animals that are unnatural hosts.

Research note Incompatibility of Protopolystoma xenopodis (Monogenea: Polystomatidae) with an octoploid Xenopus species from southern Rwanda

Protopolystoma xenopodis is an oviparous monogenean occurring as an adult in the urinary bladder of the clawed toad Xenopus laevis. Oncomiracidia invade the host’s kidneys where juveniles develop, subsequently migrating to the definitive site. In central Africa, the tetraploid X. laevis occurs in sympatry with octoploid congeners, including Xenopus wittei, believed to be the hybrid derivatives of X. laevis- and Xenopus fraseri-like parental lineages. Twenty laboratory-raised, naive specimens of an X. wittei-like species from southern Rwanda were each exposed to 30 embryonated P. xenopodis eggs (at 20°C) and screened for parasite egg production until 9 months post-exposure. These toads failed to support the development of gravid parasites (comparable experimental procedures produce at least 35% prevalence of patent infection in the natural host X. laevis). Further X. wittei aff. ( n=26) and X. laevis ( n=17) were exposed to P. xenopodis oncomiracidia and dissected at variable times post-exposure: larvae were able to invade the kidneys of X. wittei aff. and began feeding and morphological development. Severe mortality of juveniles occurred in both natural and unnatural hosts between invasion and 39 days post-exposure. However, while small numbers of parasites persisted in X. laevis, no stages were found in X. wittei aff. beyond 39 days. Present data demonstrate the incompatibility of P. xenopodis with X. wittei aff. and are consistent with a hypothesis that specificity in Protopolystoma– Xenopus systems is determined primarily by the ability of juveniles to complete development in the host’s kidneys.