Randolph and Dobson (2012) criticize the dilution effect, which describes the negative relationship between biodiversity and infectious disease risk. Unfortunately, their commentary includes distortions, errors of omission, and errors of commission, which are rebutted herein. Contrary to their claims, the dilution effect is not a ‘mantra’ that asserts that reduced disease risk is a ‘universal’ outcome of high diversity. Although universality of the dilution effect has not been claimed, and conditions under which diversity can amplify disease risk have been described, the growing literature indicates that the dilution effect is indeed a widespread phenomenon.

We are disappointed with Ostfeld's parochial commentary (Ostfeld, 2013) because we hoped we had addressed the dilution theory debate from a wider perspective, taking into account studies beyond those originating in New York State (Randolph & Dobson, 2012). We emphasized the inherent variability in the effects of biodiversity on the risk of zoonotic disease, noting explicitly that Ostfeld's own work allowed for positive, neutral and negative outcomes depending on the precise circumstances and biological interactions. The wider the range of studies, the greater the evidence for neutral and positive outcomes (i.e. biodiversity may have no effect or exacerbate infection risk) as the literature bias is gradually overcome. Publication bias, however, may still persist and be identified by appropriate meta-analyses (Salkeld et al., 2013).

Parasites in the genus Onchocerca infect humans, ruminants, camels, horses, suids, and canids, with effects ranging from relatively benign to debilitating. In North America, Onchocerca cervipedis is the sole species known to infect cervids, while at least 5 Onchocerca species infect Eurasian cervids. In this study, we report the discovery of a cervid-parasitizing Onchocerca only distantly related to O. cervipedis. To reconstruct the phylogenetic history of the genus Onchocerca, we used newly acquired DNA sequence from O. cervipedis (from moose in Northwest Territories, Canada) and from the newly discovered species (from white-tailed deer in upstate New York), as well as previously published sequences. Ancestral host reconstructions suggest that host switches have been common throughout the evolutionary history of Onchocerca, and that bovid- and cervid-parasitizing species have been particularly important sources of descendant species. North America cervids might therefore serve as a source for Onchocerca invasions into new hosts. Given the high density of deer populations, the potential for zoonotic infections may also exist. Our discovery of a new Onchocerca species with relatively limited sampling suggests that the diversity of Onchocerca associated with cervids in North America may be greater than previously thought, and surveys utilizing molecules and morphology are necessary.

Temperature is an important factor influencing the biology of ectothermic organisms and is intrinsically linked to climate change. Trematodes are potentially susceptible to temperature changes and in order to develop predictive frameworks of their responses to climate change large-scale analyses are needed. The present study, using the Q10 value, analyses experimental data from the scientific literature on the effects of temperature on cercarial development and emergence across a wide range of temperature in low (⩽35°) and mid-latitude (36–60°) species. Temperature appears to have no significant effect on the rate of development of cercariae within molluscan hosts. Data on cercarial emergence, corrected to incorporate the minimum emergence temperature threshold (METT) and acclimation status, was found to be largely unaffected by temperature over optimum ranges of ≈20 °C (15–25 °C) for mid-latitude species and ≈25 °C (20–30 °C) for low-latitude species. In addition, a decline in emergence rates was shown at higher temperatures. These results are contrary to a previous study on the meta-analysis of cercarial emergence. Some evidence of strain-specific differences and thermostability over a wide temperature range for both cercarial development and emergence was apparent. The significance of these results in furthering our understanding of cercarial biology under natural conditions is discussed.

We evaluated the effect of chemotherapy with a sequential combined treatment of a low dose of benznidazole and allopurinol, in different schedules of administration, in experimental models of acute and chronic Trypanosoma cruzi infection. Mice were infected with Nicaragua T. cruzi isolate, a virulent parasite from an endemic area of Nicaragua, genotyped as TcI (Grosso et al. 2010). We assessed survival rate, IgG levels, histopathological studies and quantified parasitaemia. A 15% survival rate was recorded in untreated mice during the acute phase of T. cruzi infection. Allopurinol administered immediately after benznidazole treatment was able to reduce parasitaemia and attenuate tissue damage by reducing inflammation. Trypanosoma cruzi-specific antibodies also decreased in 40–50% of the treated mice. The addition of allopurinol during the chronic phase showed the highest beneficial effect, not only by reducing parasitaemia but also by lowering the degree of inflammation and fibrosis.

Avian trichomonosis, caused by the flagellated protozoan Trichomonas gallinae, is a recently emerged infectious disease of British passerines. The aetiological agent, a clonal epidemic strain of the parasite, has caused unprecedented finch mortality and population-level declines in Britain and has since spread to continental Europe. To better understand the potential origin of this epidemic and to further investigate its host range, T. gallinae DNA extracts were collected from parasite culture and tissue samples from a range of avian species in Britain. Sequence typing at the ITS1/5.8S rRNA/ITS2 region resolved three distinct ITS region types circulating in free-ranging British birds. Subtyping by sequence analyses at the Fe-hydrogenase gene demonstrated further strain variation within these ITS region types. The UK finch epidemic strain was preponderant amongst columbids sampled, however, wide strain diversity was encountered in isolates from a relatively small number of pigeons, suggesting further strains present in columbid populations across the UK are yet to be identified. Fe-hydrogenase gene sequence data in isolates from birds of prey with disease were predominantly identical to the UK finch epidemic strain, demonstrating its presence as a virulent strain in UK birds of prey since at least 2009.

Decades of intensive anthelmintic treatment has caused equine large strongyles to become quite rare, while the cyathostomins have developed resistance to several drug classes. The larval culture has been associated with low to moderate negative predictive values for detecting Strongylus vulgaris infection. It is unknown whether detection of other large strongyle species can be statistically associated with presence of S. vulgaris. This remains a statistical challenge because of the rare occurrence of large strongyle species. This study used a modified Poisson regression to analyse a dataset for associations between S. vulgaris infection and simultaneous occurrence of Strongylus edentatus and Triodontophorus spp. In 663 horses on 42 Danish farms, the individual prevalences of S. vulgaris, S. edentatus and Triodontophorus spp. were 12%, 3% and 12%, respectively. Both S. edentatus and Triodontophorus spp. were significantly associated with S. vulgaris infection with relative risks above 1. Further, S. edentatus was associated with use of selective therapy on the farms, as well as negatively associated with anthelmintic treatment carried out within 6 months prior to the study. The findings illustrate that occurrence of S. vulgaris in larval cultures can be interpreted as indicative of other large strongyles being likely to be present.

The cyclooctadepsipeptide PF1022A and the aminophenylamidines amidantel, deacylated amidantel (dAMD) and tribendimidine were tested as examples for drug classes potentially interesting for development as anthelmintics against human helminthiases. These compounds and levamisole were tested alone and in combination to determine their efficacy against the rat hookworm Nippostrongylus brasiliensis. After three oral treatments, intestinal worms were counted. Drug effects on parasite morphology were studied using scanning electron microscopy (SEM). Plasma pharmacokinetics were determined for tribendimidine and dAMD. All drugs reduced worm burden in a dose-dependent manner, however amidantel was significantly less active than the other aminophenylamidines. Combinations of tribendimidine and dAMD with levamisole or PF1022A at suboptimal doses revealed additive effects. While PF1022A caused virtually no changes in morphology, levamisole, dAMD and tribendimidine caused severe contraction, particularly in the hind body region. Worms exposed to combinations of PF1022A and aminophenylamidines were indistinguishable from worms exposed only to aminophenylamidines. After oral treatment with tribendimidine, only the active metabolite dAMD was detectable in plasma and concentrations were not significantly different for oral treatment with dAMD. The results support further evaluation of cyclooctadepsipeptides alone and in combination with cholinergic drugs to improve efficacy. Combining these with registered drugs may help to prevent development of resistance.

The necessity to easily establish Histomonas meleagridis cultures has been underlined extensively by many researchers in order to gain more insights in the biology of H. meleagridis. In addition the occurrence of different protozoa in the caeca of birds impedes, however, the isolation and propagation of H. meleagridis from field outbreaks. Therefore, in a kinetic study using transmission electron microscopy the deleterious effects of adventitious protozoa including Tetratrichomonas gallinarum and Blastocystis spp. on cultured H. meleagridis were examined. To overcome this issue, an easy and successful approach to establish the mono-eukaryotic H. meleagridis culture free of other host's protozoa is proposed. At 10 days post infection, liver lesions of H. meleagridis-infected birds were isolated and inoculated into culture media pre-incubated with caecal bacteria. After 48 h of incubation, presence of H. meleagridis in the cultures was confirmed through morphological evaluation. Additionally, TEM examination and analysis by PCR amplification of the small subunit rRNA gene could exclude the co-cultivation of T. gallinarum and Blastocystis spp. Furthermore, after successful propagation and maintenance of the cultured H. meleagridis, its pathogenicity was affirmed in an infection experiment in turkeys.

When investigating parasite–host dynamics in wild populations, a fundamental parameter to investigate is prevalence. This quantifies the percentage of individuals infected in the population. Investigating how prevalence changes over time and space can reveal interesting aspects in the parasite–host relationship in natural populations. We investigated the dynamic between a common avian parasite (Syngamus trachea) in a host metapopulation of house sparrows (Passer domesticus) on the coast of Helgeland in northern Norway. We found that parasite prevalence varied in both time and space. In addition, the parasite prevalence was found to be different between demographic groups in the local populations. Our results reveal just how complex the dynamic between a host and its parasite may become in a fragmented landscape. Although temperature may be an important factor, the specific mechanisms causing this complexity are not fully understood, but need to be further examined to understand how parasite–host interactions may affect the ecological and evolutionary dynamics and viability of host populations.

A study was carried out to investigate whether the action of triclabendazole sulphoxide (TCBZ.SO) against the liver fluke, Fasciola hepatica is altered by inhibition of P-glycoprotein (Pgp)-linked drug efflux pumps. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible fluke isolates were used for this in vitro study and the Pgp inhibitor selected was R(+)-verapamil [R(+)-VPL]. For experiments with the Oberon isolate, flukes were incubated for 24 h with either R(+)-VPL (1×10−4m) on its own, TCBZ.SO (15 μg mL−1) alone, a combination of R(+)-VPL (1×10−4m) plus TCBZ.SO (15 μg mL−1), TCBZ.SO (50 μg mL−1) on its own, or a combination of TCBZ.SO (50 μg mL−1) plus R(+)-VPL (1×10−4m). They were also incubated in TCBZ.SO (50 μg mL−1) alone or in combination with R(+)-VPL (1×10−4m) until they became inactive; and in TCBZ.SO (50 μg mL−1) alone for a time to match that of the combination inactivity time. Flukes from the Cullompton isolate were treated with either TCBZ.SO (50 μg mL−1) alone or in combination with R(+)-VPL (1×10−4m) until they became inactive, or with TCBZ.SO (50 μg mL−1) alone time-matched to the combination inactivity time. Morphological changes resulting from drug treatment and following Pgp inhibition were assessed by means of scanning electron microscopy. Incubation in R(+)-VPL alone had a minimal effect on either isolate. TCBZ.SO treatment had a relatively greater impact on the TCBZ-susceptible Cullompton isolate. When R(+)-VPL was combined with TCBZ.SO in the incubation medium, however, the surface disruption to both isolates was more severe than that seen after TCBZ.SO treatment alone; also, the time taken to reach inactivity was shorter. More significantly, though, the potentiation of drug activity was greater in the Oberon isolate; also, it was more distinct at the higher concentration of TCBZ.SO. So, the Oberon isolate appears to be particularly sensitive to efflux pump inhibition. The results of this study suggest that enhanced drug efflux in the Oberon isolate may be involved in the mechanism of resistance to TCBZ.

Angiostrongylus cantonensis is a parasitic nematode of rodents and a leading aetiological agent of eosinophilic meningitis in humans. Definitive diagnosis is difficult, often relying on immunodiagnostic methods which utilize crude antigens. New immunodiagnostic methods based on recombinant proteins are being developed, and ideally these methods would be made available worldwide. Identification of diagnostic targets, as well as studies on the biology of the parasite, are limited by a lack of molecular information on Angiostrongylus spp. available in databases. In this study we present data collected from DNA random high-throughput sequencing together with proteomic analyses and a cDNA walking methodology to identify and obtain the nucleotide or amino acid sequences of unknown immunoreactive proteins. 28 080 putative ORFs were obtained, of which 3371 had homology to other deposited protein sequences. Using the A. cantonensis genomic sequences, 156 putative ORFs, matching peptide sequences obtained from previous proteomic studies, were considered novel, with no homology to existing sequences. Full-length coding sequences of eight antigenic target proteins were obtained. In this study we generated not only the complete nucleotide sequences of the antigenic protein targets but also a large amount of genomic data which may help facilitate future genomic, proteomic, transcriptomic or metabolomic studies on Angiostrongylus.

Freshwater gammarids infected with the acanthocephalan parasite Polymorphus minutus show behavioural alterations but also differ from uninfected individuals in their appearance because of the carotenoid-based colouration of the parasite visible through the cuticle. However, it's not clear whether this phenotypic alteration is an adaptation favouring parasite transmission to the definitive host. To test this hypothesis, we investigated the selective preference of mallard towards two prey types: uninfected gammarids on which we applied a dot of inconspicuous brown paint, and uninfected gammarids on which we applied a dot of bright orange paint to mimic the change in appearance due to P. minutus without changes in host behaviour. Mallards showed a significant preference for orange-painted gammarids regardless of how gammarids were distributed (isolated or aggregated). This suggests that parasite's colouration may play a role in enhanced transmission to definitive avian hosts. The role of P. minutus’ colouration in the conspicuousness of gammarids has however to be balanced by the extent to which mallards use visual cues to forage in the field. From the perspective of a multidimensional manipulation, this study suggests that the change in appearance may act synergistically with the changes in behaviour to promote transmission to waterbirds.

Gene flow maintains the genetic integrity of species over large spatial scales, and dispersal maintains gene flow among separate populations. However, body size is a strong correlate of dispersal ability, with small-bodied organisms being poor dispersers. For parasites, small size may be compensated by using their hosts for indirect dispersal. In trematodes, some species use only aquatic hosts to complete their life cycle, whereas others use birds or mammals as final hosts, allowing dispersal among separate aquatic habitats. We performed the first test of the universality of the type of life cycle as a driver of parasite dispersal, using a meta-analysis of 16 studies of population genetic structure in 16 trematode species. After accounting for the geographic scale of a study, the number of populations sampled, and the genetic marker used, we found the type of life cycle to be the best predictor of genetic structure (Fst): trematode species bound to complete their life cycle within water showed significantly more pronounced genetic structuring than those leaving water through a bird or mammal host. This finding highlights the dependence of parasites on host traits for their dispersal, suggesting that genetic differentiation of parasites reflects the mobility of their hosts.