Summary1. Measuring the degree of skin-swelling induced by intradermal injection of phytohemagglutinin (PHA) is simple, quick and inexpensive, does not require specialized equipment and is easily conducted under field conditions. 2. PHA is perhaps the most frequently used assay of immunocompetence in field studies of birds. However, the method has rarely been used, and never validated, for studies on ectothermic vertebrates. 3. Here, we document its use in an amphibian. In response to PHA injected into a toe web, cane toads exhibited a 35% increase in web thickness 24 h postinjection. 4. Histologically, PHA injection initiated a rapid (<12 h) infiltration of neutrophils, eosinophils and macrophages at the injection site, followed by an influx of lymphocytes by 24 h postinjection. A second exposure to PHA stimulated a faster, more intense swelling response. 5. In cane toads, PHA injection elicits a rapid innate immune response, followed by a secondary response that may reflect cell-mediated immune activity. Both components are easily quantifiable by the degree of skin-swelling. 6. Hence, PHA injection offers a convenient assay to quantify immune function in anurans and could usefully be incorporated into studies on the reasons for global amphibian declines.

The impact of invasive species on biodiversity has attracted considerable study, but impacts of the invasion process on the invaders themselves remain less clear. Invading species encounter conditions different from those in their ancestral habitats and are subject to intense selection for rapid dispersal. The end result may be significant stress on individual organisms, with consequent health problems. Our studies on invasive cane toads in Australia reveal severe spinal arthritis in Ϸ10% of large adult toads, associated with the same factors (large body size, frequent movement, and relatively long legs) that have enabled toads to invade so rapidly across the Australian tropics.anuran ͉ invasive species ͉ locomotion ͉ spondylitis ͉ colonization

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At an invasion front, energetic and physiological trade‐offs may differ from those at the range‐core as a result of selection for enhanced dispersal, combined with a low density of conspecifics (which reduces pathogen transmission and competition for food). We measured traits related to energy stores and immunity in wild cane toads (Rhinella marina) across a 750‐km transect from their invasion front in tropical Australia, back into sites colonized 21 years earlier. Several traits were found to vary with population age; some linearly and others in a curvilinear manner. The relative size of spleens and fat bodies was highest in the oldest and newest populations, where rates of lungworm infection were lowest. Toads from older populations produced more corticosterone in response to a standardized stressor, and had higher lymphocyte counts (but lower basophil counts). The amount of skin swelling elicited by phytohaemagglutinin injection did not vary geographically, although recruitment of leukocytes to the injected tissue was higher in toads from long‐colonized areas. Because this was a field‐based study, we cannot differentiate the effects of population age, toad density or pathogen pressure on our measures of stress and immune responses, nor can we distinguish whether the causation involves hard‐wired adaptive processes or phenotypically plastic responses. Nonetheless, our data demonstrate substantial variation in immune systems among toads at varying distances from an invasion front, showing that a biological invasion imposes strong pressures on physiological systems of the invader.

We observed an outbreak of necrotizing fasciitis associated with Streptococcus agalactiae infection in a group of juvenile saltwater crocodiles (Crocodylus porosus). We undertook screening of crocodiles and the environment to clarify the source of the outbreak and evaluated the isolates cultured from post-mortem specimens with molecular methods to assess clonality and the presence of known group B streptococcal virulence determinants. The isolates were indistinguishable by pulsed-field gel electrophoresis. They were a typical serotype Ia strain with the Calpha-like protein gene, epsilon (or alp1), the mobile genetic elements IS381 ISSag1 and ISSag2, and belonged to multi-locus sequence type (ST) 23. All of these characteristics suggest they were probably of human origin. We review the medical and veterinary literature relating to S. agalactiae necrotizing fasciitis, epidemiology and virulence determinants.

ABSTRACT:Host-parasite systems have often evolved over time, such that infection dynamics may become greatly modified from the time of initial contact of the host with the parasite. Biological invasions may be useful to clarify processes in the initial contact of hosts with parasites, and allow us to compare parasite uptake between the ancestral (coevolved) host and novel (noncoevolved) hosts. Cane toads (Bufo marinus) are spreading rapidly through tropical Australia, carrying with them a nematode lungworm (Rhabdias pseudosphaerocephala) congeneric with those found in Australian frogs. We investigated the dynamics of infections of the toad parasite by conducting histologic examinations of cane toads and three native Australian frogs (Litoria dahlii, Litoria nasuta, and Opisthodon ornatus) at 2, 6, and 10 days after experimental exposure to the toad lungworm. More worms were found in toads than in frogs, especially at longer periods postexposure. In toads, the infective larvae entered the skin and muscles within 2 days postexposure, passed into the coelom in 6 days, and reached the lungs at 10 days. In frogs, larvae were found in many organs rather than migrating to consistent target tissues; a few larvae reached the lungs of L. dahlii. Migratory larvae caused increasing inflammation (primarily granulomatous admixed with granulocytes then lymphocytes) through time, especially in frogs. Evolution has resulted in an enhanced ability of the lungworm to locate the target organ (the lungs) of the toad, and an increase in rates of parasite survival within this host.

Although much research in evolutionary ecology is based upon the premise that high levels of parasitism impair the host's functioning, the assumed link between parasitism and fitness has been assessed for relatively few kinds of animals. At our study site in tropical Australia, keelback snakes (Tropidonophis mairii (Gray, 1841), Colubridae) are heavily infected with haemogregarine blood parasites: 90% of snakes that we tested carried the parasite, with the proportion of erythrocytes containing haemogregarines averaging 15% and ranging up to a remarkable 64%. Prevalence increased with snake body size, but intensity decreased with age. Unlike lizards studied previously, the snakes did not respond to haemogregarine infection by releasing immature erythrocytes into the circulation. In striking contrast to results from a recent study on a sympatric snake species, we did not find any empirical links between parasite numbers and several measures of host fitness (body condition, growth rate, feeding rate, antipredator behaviour, locomotor performance, reproductive status, reproductive output, and recapture rate). The association between this parasite and its host thus appears to be surprisingly benign, suggesting that host-parasite interactions sometimes may have only trivial consequences for host fitness in natural populations. Plausibly, host-parasite coevolution weakens or eliminates fitness costs of parasitism.Résumé : Bien que beaucoup de recherches en écologie évolutive soient basées sur la prémisse que de forts niveaux de parasitisme nuisent au fonctionnement de l'hôte, on a évalué le lien présumé entre le parasitisme et la fitness chez relativement peu de sortes d'animaux. À notre site d'étude en Australie tropicale, les couleuvres à carène dorsale (Tropidonophis mairii (Gray, 1841), Colubridae) sont fortement infectées d'hémogrégarines parasites du sang; 90 % des couleuvres examinées portent le parasite et, en moyenne, 15 % des érythrocytes contiennent des hémogrégarines; ce pourcentage peut atteindre 64 %, ce qui est exceptionnel. La prévalence du parasitisme augmente en fonction de la taille des couleuvres, mais l'intensité diminue avec l'âge. Contrairement aux lézards étudiés précédemment, les couleuvres ne réagissent pas à l'infection par les hémogrégarines en libérant dans leur circulation des érythrocytes immatures. En contraste frappant avec les résultats d'une étude récente sur une espèce sympatrique de couleuvre, il n'existe pas de lien empirique entre le nombre de parasites et les différentes mesures de la fitness de l'hôte (condition corporelle, taux de croissance, taux d'alimentation, comportement antiprédateur, performance locomotrice, statut reproductif, rendement reproductif et taux de recapture). De façon inattendue, l'association entre ce parasite et son hôte semble donc bénigne, ce qui laisse croire que les interactions hôte-parasite peuvent quelquefois n'avoir que des conséquences triviales sur la fitness de l'hôte dans les populations naturelles. Il apparaît plausible que la coévolution hôte-...

The genus Brucella comprises various species of both veterinary and human medical importance. All species are genetically highly related to each other, sharing intra-species average nucleotide identities (ANI) of > 99%. Infections occur among various warm-blooded animal species, marine mammals, and humans. Until recently, amphibians had not been recognized as a host for Brucella. In this study, however, we show that novel Brucella species are distributed among exotic frogs worldwide. Comparative recA gene analysis of 36 frog isolates from various continents and different frog species revealed an unexpected high genetic diversity, not observed among classical Brucella species. In phylogenetic reconstructions the isolates consequently formed various clusters and grouped together with atypical more distantly related brucellae, like B. inopinata, strain BO2, and Australian isolates from rodents, some of which were isolated as human pathogens. Of one frog isolate (10RB9215) the genome sequence was determined. Comparative genome analysis of this isolate and the classical Brucella species revealed additional genetic material, absent from classical Brucella species but present in Ochrobactrum, the closest genetic neighbor of Brucella, and in other soil associated genera of the Alphaproteobacteria. The presence of gene clusters encoding for additional metabolic functions, flanked by tRNAs and mobile genetic elements, as well as by bacteriophages is suggestive for a different ecology compared to classical Brucella species. Furthermore it suggests that amphibian isolates may represent a link between free living soil saprophytes and the pathogenic Brucella with a preferred intracellular habitat. We therefore assume that brucellae from frogs have a reservoir in soil and, in contrast to classical brucellae, undergo extensive horizontal gene transfer.