An exact confidence set for two binomial proportions and exact unconditional confidence intervals for the difference and ratio of proportions

Sarcocystis spp. Macrocysts Infection in Wildfowl Species in Eastern Baltic Region: Trends in Prevalence in 2011-2022

Wildfowl meat infected with S. rileyi macrocysts is not suitable for human consumption. Ducks are among the main game birds in Europe, and S. rileyi infections cause significant economic losses. In 2011-2022, a total of 2649 anseriforms collected in Lithuania and 619 Mallards (Anas platyrhynchos) hunted in the Kaliningrad region of Russia, Belarus, and Latvia were tested for macrocysts. In Lithuania, macrocysts were detected in 206 of 2362 Mallards (8.7%) and in two of 88 (2.3%) Eurasian Teals (Anas crecca). The prevalence of macrocysts in the other three countries, Belarus (5.9%), Russia (5.0%), and Latvia (3.1%), was similar. For species identification, macrocysts isolated from 37 Mallards (21 from Lithuania, 8 from Russia, 6 from Belarus, and 2 from Latvia) were subjected to sequencing of the ITS1 region. Based on DNA analysis, S. rileyi was confirmed in all tested birds. By comparing the infection rates of macrocysts in Mallards in Lithuania, significant differences were observed in different years (p = 0.036), and a significantly higher prevalence of infection was established in November-December than in September-October (p = 0.028). Given the amount of data per decade on the prevalence of S. rileyi, awareness of infection needs to be increased.

Molecular Confirmation of Accipiter Birds of Prey as Definitive Hosts of Numerous Sarcocystis Species, including Sarcocystis sp., Closely Related to Pathogenic S. calchasi

The present study aimed to test intestinal scrapings of the Northern Goshawk (Accipiter gentilis) and the Eurasian Sparrowhawk (Accipiter nisus) from Lithuania for S. calchasi and other Sarcocystis species characterised by bird-bird life cycles. The protozoan parasite Sarcocystis calchasi can cause respiratory and neurological diseases in a variety of birds; however, the distribution of this parasite is not well-examined. Sarcocystis species were identified with nested PCR and sequencing of the partial ITS1 region. Sporocysts and/or sporulated oocysts of Sarcocystis spp. were observed in 16 (100%) Northern Goshawks and 9 (56.3%) Eurasian Sparrowhawks. Four species, S. columbae, S. halieti, S. turdusi, and S. wobeseri, were confirmed in the Eurasian Sparrowhawk. Apart from the latter four species, S. calchasi, S. cornixi, S. kutkienae, and S. lari were established in the Northern Goshawk. A higher prevalence of Sarcocystis spp. and species richness in Northern Goshawks is associated with the differences in the diet of two examined Accipiter species. This study is the first report of S. calchasi in Lithuania. Furthermore, the genetically distinct species Sarcocystis spp. 23LTAcc, which is most closely related to S. calchasi, was found in three Northern Goshawks.

Molecular Identification of Sarcocystis rileyi and Sarcocystis sp. (Closely Related to Sarcocystis wenzeli) in Intestines of Mustelids from Lithuania

The genus Sarcocystis is a group of numerous protozoan parasites having a two-host life cycle. Based on laboratory experiments and/or phylogenetic analysis results it was shown that seven Sarcocystis spp. producing sarcocsyts in bird tissues are transmitted via predatory placental mammals. To date the role of small mammals of the family Mustelidae in the distribution of avian Sarcocystis spp. have not been studied. During the current investigation, intestinal mucosa scrapings of 115 mustelids belonging to five species were tested for S. albifronsi, S. anasi, S. rileyi, and S. wenzeli infecting anseriforms and chickens. Microscopically, free sporocysts, sporulating oocysts, and loose oocysts were found in 61 samples (53.0%). Using nested PCR targeting the ITS1 region and sequencing, S. rileyi was confirmed in eight American minks, two European polecats and single European badger. Sarcocystis sp. was identified in one American mink and one European pine marten. Based on the partial ITS1 region this parasite showed that 100% identity to pathogenic Sarcocystis sp. caused a fatal infection in backyard chickens from Brazil. Phylogenetically, the Sarcocystis sp. identified in our study was most closely related to S. wenzeli parasitising domestic fowl (Gallus domesticus).

Helminth Assemblages of the Antarctic Black Rockcod, Notothenia coriiceps (Actinopterygii: Nototheniidae) in Coastal Waters near Galindez Island (Argentine Islands, West Antarctic): Temporal Changes in the Endoparasite Community

PURPOSE

Analysis and comparison of the helminth assemblages in Antarctic rockcod Notothenia coriiceps collected near the UAS "Akademik Vernadsky" (Argentine Islands, West Antarctica) in 2002 and 2014-2015 were performed to characterise the parasite community and investigate the temporal changes in helminth assemblages and infection parameters.

METHODS

All specimens of N. coriiceps (n = 194) were caught at depths of 10-30 m. Parasites (22,856 helminth specimens and 15,057 cysts) were collected manually and identified based on their morphology. Statistical analysis of the quantitative data was performed using the Quantitative Parasitology 3.0 (QP 3.0), Paleontological Statistics (PAST v. 3.1), and PRIMER 6 software.

RESULTS

Twenty-seven species of four taxonomic groups were recorded: trematodes (8 species), cestodes (4), nematodes (5), and acanthocephalans (10). Helminth samples collected in 2002 and 2014-2015 showed a rather high similarity in species composition. The species richness was higher in the sample collected in 2014-2015, while the evenness and diversity in the two samples were similar. The dissimilarity between helminth infracommunities in the two samples appeared to be statistically significant. Larval cestodes Diphyllobotrium sp., the acanthocephalan Metacanthocephalus rennicki, and the trematode Neoleoburia antarctica were found to make the most significant impact on the dissimilarity.

CONCLUSIONS

The analysis of the composition and structure of helminth community in N. coriiceps revealed the changes that have happened during the last decade. At least some of the changes are attributed to the changes in marine ecosystems in Western Antarctica.

The Role of Birds of the Family Corvidae in Transmitting Sarcocystis Protozoan Parasites

Simple Summary

Members of the genus Sarcocystis are protozoan parasites that infect mammals, birds, and reptiles. Sarcocystis spp. have an obligatory two-host prey-predator life cycle. Sarcocysts form in the muscles and central nervous system of the intermediate host, while oocysts and sporocysts develop in the small intestine of the definitive host. There is a lack of studies on omnivorous birds of family Corvidae as potential definitive hosts of Sarcocystis spp. Until now, only S. ovalis has been confirmed to be transmitted via corvids. In the current study, 91 small intestine samples from six corvid species from Lithuania were examined for the presence of Sarcocystis spp. that use birds, carnivorous mammals, and cervids as intermediate hosts. Oocysts of Sarcocystis spp. were observed in 43 samples (47.3%) using a light microscope. Based on molecular methods, 11 Sarcocystis spp., (S. columbae, S. cornixi, S. halieti, S. kutkienae, S. lari, S. turdusi, S. wobeseri, S. arctica, S. lutrae, S. ovalis, and S. oviformis) were identified. These results indicate that corvids may transmit some species of Sarcocystis that use birds and mammals as intermediate hosts.

Abstract

Members of the family Corvidae are ecologically flexible omnivorous birds, particularly adaptive to urban habitats, and living in proximity to humans; these birds may serve as definitive hosts (DH) for Sarcocystis spp., but research about this is lacking. In the present study, intestinal samples from 91 corvids collected in Lithuania were molecularly tested by species-specific PCR targeting the ITS1 and cox1 genes and subsequently sequenced for the presence of Sarcocystis spp. Under a light microscope, oocysts of Sarcocystis spp. were observed in 43 samples (47.3%), while molecular methods, detected Sarcocystis spp. in 77 birds (84.6%). Eleven Sarcocystis spp. (S. columbae, S. cornixi, potentially pathogenic S. halieti, S. kutkienae, S. lari, S. turdusi, S. wobeseri, S. arctica, S. lutrae, S. ovalis, and S. oviformis) were identified in the intestinal samples from six corvid species from Lithuania. Infections with multiple Sarcocystis spp. were detected in 79.2% of the infected corvid birds. Three of the identified Sarcocystis spp. use corvids as intermediate hosts (IH); therefore, corvids may serve as IH and DH of the same Sarcocystis species. Based on molecular results and on corvid diet, omnivorous corvids may play an important role in transmitting Sarcocystis spp.

Molecular identification and epidemiological data of Anisakis spp. (Nematoda: Anisakidae) larvae from Southeastern Pacific Ocean off Peru

The objective of this study is to determine the infection status of nematode larvae and record epidemiological molecular data in commercial fish from the southeast Pacific off the central coast of Peru. Anisakiasis is a fish-borne zoonosis caused by Anisakis larvae, parasites of relevance in the fishery resources that have negative impact on public health. Between January 2012 to December 2014, 345 specimens of four fish species (Trachurus symmetricus murphyi, Scomber japonicus peruanus, Merluccius gayi peruanus and Seriolella violacea) were examined for Anisakis sp. larvae. A total of 997 Anisakis sp. larvae were found in the body cavity of 196 fish (total prevalence 53.7%, total mean intensity 5.08). After morphological analysis, 958 (96.08%) larvae were identified as Type I and 39 (3.92%) as Type II. Specimens were identified by molecular analysis of the mitochondrial cytochrome c oxidase subunit II (cox2) gene, confirming that A. pegreffii is the predominant species and the most important agent of human anisakiasis off the Peru Central Coast. In addition, we revealed the occurrence of A. physeteris (s.l.) in S. japonicus peruanus (P = 18.0%; MI = 2.17).

Therefore, the results obtained in the present study improve the knowledge of the occurrence of Anisakis species in the commercial fish from the Southeastern Pacific Ocean, highlighting the importance of considering a potential hazard for humans and the necessity of further research in other fishes of greater preference by the Peruvian population.

•

Anisakiasis is a fish-borne zoonosis caused by larvae of the nematode Anisakis sp. present in fish.

•

The dominant species on the central coast of the Peruvian Sea is A. pegreffii.

•

A. physeteris (s.l.) was found parasitizing only one host with a low prevalence.

•

Widespread occurrence of Anisakis sp. in wild sea fish.

On matching confidence intervals and tests for some discrete distributions: methodological and computational aspects

Exact two-tailed tests and two-sided confidence intervals (CIs) for a binomial proportion or Poisson parameter by Sterne (Biometrika 41:117–129, 1954) or Blaker (Can J Stat 28(4):783–798, 2000) are successful in reducing conservatism of the Clopper–Pearson method. However, the methods suffer from an inconsistency between the tests and the corresponding CIs: In some cases, a parameter value is rejected by the test, though it lies in the CI. The problem results from non-unimodality of the test p value functions. We propose a slight modification of the tests that avoids the inconsistency, while preserving nestedness and exactness. Fast and accurate algorithms for both the test modification and calculation of confidence bounds are presented together with their theoretical background.

Alaria alata mesocercariae prevalence and predilection sites in amphibians in Latvia

Alaria alata is known as a trematode with a complex life cycle. The trematode Alaria alata infects amphibians as second intermediate hosts. In the present study, we examined 390 amphibians-European water frogs Pelophylax esculentus complex (n = 335), common frogs Rana temporaria (n = 19), moor frogs Rana arvalis (n = 3), and common toads Bufo bufo (n = 30) collected from randomly selected wetland habitats in Latvia. Out of all examined specimens, 80 were tadpoles and 310 were adult amphibians. Mesocercariae of A. alata was detected in 108 specimens from all examined amphibian species, except the common toad, reaching the overall prevalence of 27.7%. Tadpoles were found to be more frequently infected with A. alata, when compared with adults, 58.8% and 22.4%, respectively. The results showed that mesocercariae accumulate in visceral membranes, different internal organs, and muscles in the head area. This is a comprehensive study to identify A. alata mesocercariae predilection sites in amphibians.

Molecular Identification of Zoonotic Parasites of the Genus Anisakis (Nematoda: Anisakidae) from Fish of the Southeastern Pacific Ocean (Off Peru Coast)

The study aims to perform, for the first time, the molecular identification of anisakid larvae in commercial fish from the Southeastern Pacific Ocean off the Peru coast, and to provide data on their infection level by fishing ground, fish host, and site of infection. Fish specimens (N = 348) from the northern and the central coast of Peru were examined for parasites. The fish fillets were examined by the UV-press method. Anisakis spp. larvae (N = 305) were identified by mtDNA cox2 sequences analysis and by the ARMS-PCR of the locus nas10 nDNA. Two hundred and eighty-eight Anisakis Type I larvae corresponded to Anisakis pegreffii, whereas 17 Anisakis Type II larvae clustered in a phylogenetic lineage distinct from Anisakis physeteris deposited in GenBank, and corresponding to a phylogenetic lineage indicated as Anisakis sp. 2, previously detected in fish from both Pacific and Atlantic waters. Anisakis pegreffii was found to infect both the flesh and viscera, while Anisakis sp. 2 occurred only in the viscera. The average parasitic burden with A. pegreffii in the examined fish species from the two fishing grounds was significantly higher than that observed with Anisakis sp. 2. The results obtained contribute to improve the knowledge on the distribution and occurrence of Anisakis species in Southeastern Pacific waters and their implications in seafood safety for the local human populations.

The wild boar (Sus scrofa, Linnaeus, 1758) as an important reservoir host for Alaria alata in the Baltic region and potential risk of infection in humans

Alaria alata trematode is widely distributed throughout Europe and has a complex life cycle in which wild boar serve as a reservoir host. The primary aims of the present study are to establish the occurrence of A. alata mesocercariae in naturally infected wild boar in Latvia and to assess the risk for humans to acquire A. alata infection via consumption of wild boar meat. By summarizing long-term data using the Trichinella inspection method from 2014 to 2019, the overall A. alata prevalence was 8.3%, of which significantly higher A. alata prevalence was observed during the summer seasons. Additionally, 43.9% (n = 485) of wild boar were found to be infected with A. alata using Alaria mesocercariae migration technique. The present study indicates that the probability for humans to acquire A. alata mesocercariae is possible, yet improbable and varies from 0.2% to 2.2%. Most likely, it depends on both frequency of A. alata presence in wild boar population and of a method of preparing wild boar meat for consumption that will allow for the parasite inactivation.

Helminth Species and Infracommunities in Frogs Pelophylax ridibundus and P. esculentus (Amphibia: Ranidae) in Northern Ukraine

PURPOSE

The study aims to characterise and compare the helminth assemblages and helminth infracommunities in the marsh frog, Pelophylax ridibundus and the edible frog, P. esculentus collected in the northern part of Ukraine.

METHODS

Occurrence and abundance of the helminths were analysed by calculating the prevalence, intensity, and mean abundance of infection; similarities between the infracommunities were estimated by the Bray-Curtis index and visualised using nMDS plots. Dissimilarities were estimated using the ANOSIM and SIMPER routines.

RESULTS

In total, 27 helminth species were found in 143 frogs. Pelophylax ridibundus (n = 86) harboured 20 species of helminths, 24 species were found in P. esculentus (n = 57), and 17 species were shared by the two hosts. Oswaldocruzia bialata and larval Strigea sp. were absent in P. ridibundus, while they reached the prevalence of 30% and 10%, respectively, in P. esculentus. Cosmocerca ornata, Diplodiscus subclavatus, Opisthioglyphe ranae, and Codonocephalus urniger had significantly larger prevalence in P. ridibundus, whereas Haematoloechus asper was found to be more prevalent in P. esculentus. Acanthocephalus ranae, Icosiella neglecta, Haematoloechus variegatus, Pleurogenes claviger, Pleurogenoides medians, and Prosotocus confusus were equally common in both hosts. Helminth infracommunities in the two hosts had identical species richness (1-10 species, 4 on average); abundance was significantly higher in P. ridibundus.

CONCLUSIONS

Helminth assemblages of the two hosts in northern Ukraine are rather similar; however, small but significant differences were found in their species composition, parameters of infection in some species, and structure of helminth infracommunities.

Biostatistics for Parasitologists - A Primer to Quantitative Parasitology

The aggregated distributions of host-parasite systems require several different infection parameters to characterize them. We advise readers how to choose infection indices with clear and distinct biological interpretations, and recommend statistical tests to compare them across samples. A user-friendly and free software is available online to overcome technical difficulties.

Respiratory and Cardiopulmonary Nematode Species of Foxes and Jackals in Serbia

As part of routine monitoring of foxes (Vulpes vulpes) and jackals (Canis aureus) on the territory of Vojvodina province (northern Serbia), an analysis of respiratory and cardiopulmonary parasitic nematodes was conducted. Both host species harbored Eucoleus aerophilus, E. boehmi and Crenosoma vulpis, whereas Angiostrongylus vasorum was found only in foxes. A high prevalence of infection (72.6 %) was noted for E. aerophilus in foxes. The remaining parasite species occurred less frequently in both host species. In all species where it could be quantified, a high degree of parasite aggregation within host individuals was noted. Single species infections were most common, whereas two and three species infections occurred less frequently in both host species. The distribution of abundance of E. aerophilus was affected by host sex, with abundances higher in male foxes. Sampling site and year influenced abundance variation in E. boehmi.

Geographic and host size variations as indicators of Anisakis pegreffii infection in European pilchard (Sardina pilchardus) from the Mediterranean Sea: Food safety implications

European pilchards are traditionally eaten marinated or salted in the Mediterranean countries often without thermal processing or gutting due to small size. Since ingestion of live third stage Anisakis larvae represents a causing agent in the onset of anisakiasis, the aim of our study was to assess prevalence and intensity of Anisakis infection in European pilchards originating from different Mediterranean regions in a three-year sampling period (2013-2015). A total of 1564 specimens of European pilchard collected from two geographically distinct sampling regions (western Mediterranean and Adriatic Sea) were examined using the UV-Press method, which utilises the fluorescence of frozen anisakids in flattened and subsequently frozen fillets and viscera. A subsample of 67 isolated larvae was identified as A. pegreffii by diagnostic allozyme markers and sequence analyses of the mtDNA cox2 locus. The overall prevalence in pilchards was 12.2% (range 0-44.9% for different sampling points) and mean intensity 1.8. More importantly, we have observed an overall larval prevalence of 1.5% in fillets. The highest prevalence (44.9%) was recorded in pilchards caught in western parts of the Mediterranean. As fish host size was a significant predictor of parasite abundance, it should be highlighted that these pilchards were also the largest (mean total length 173.2mm); on average >2cm larger than the rest of the samples. Other isolated nematode species included Hysterothylacium sp. in viscera, showing almost a double of A. pegreffii prevalence, 20.1%. In summary, our study demonstrates that the presence of A. pegreffii in European pilchards from the Mediterranean Sea is highly influenced by both geographic and host size variation. This implies that, before future risk management measures are developed, these variables should be assessed in order to minimize public health concerns.

Monorchis lewisi n. sp. (Trematoda: Monorchiidae) from the surf bream, Acanthopagrus australis (Sparidae), in Moreton Bay, Australia

We describe Monorchis lewisi n. sp. (Monorchiidae) from the surf bream, Acanthopagrus australis (Günther, 1859) (Sparidae), in Moreton Bay, eastern Australia. The new species differs from most existing species of Monorchis Monticelli, 1893 in its possession of an elongate I-shaped excretory vesicle, and from other congeners in the relative configuration of the gut and suckers. Ovipusillus mayu Dove & Cribb, 1998 is re-reported from Gnathanodon speciosus (Forsskål, 1775) (Carangidae) from Moreton Bay. We report new second internal transcribed spacer (ITS2) and 28S rDNA sequence data for both species. Bayesian inference and Maximum Likelihood analyses of the 28S rDNA dataset suggest that existing subfamily and genus concepts within the family require substantial revision.

Richness, infestation and specificity of spinturnicid mites (Acari: Spinturnicidae) on bats in southern Oaxaca, Mexico

Studies of mites on bats in the Mexican state Oaxaca are scarce. Our objective was therefore to evaluate the richness, infestation, and specificity of spinturnicid mites on bats in southern Oaxaca, Mexico. Bats were monthly captured from April 2010 to February 2011, in four sites using four mist-nets; also, we visited natural (crevices) and artificial roosts (tunnel). Of each bat we account the number of spinturnicid mites, considering the area of the body where they were collected. Mites were preserved in 70 % ethanol and later they were mounted on microscope slides in Hoyer's medium. We captured bats of 15 species, of which eight species were infested. We recorded seven spinturnicid mites: five of the genus Periglischrus, one of the genus Cameronieta, and one of the genus Mesoperiglischrus. Periglischrus caligus, P. iheringi, and Periglischrus sp. are new records on Artibeus lituratus, Glossophaga soricina, and G. commissarisi, respectively. More infested bat species were Artibeus jamaicensis (93.8 %), A. lituratus (88.9 %), G. commissarisi and Sturnira parvidens (both 66.7 %). Prevalence of A. jamaicensis and A. lituratus was significantly higher than most other bat species. Although prevalence percentage was high, mean and median intensity were low. Spinturnicid mites were recorded in particular areas of a bat's body; therefore, they could be an additional tool for the taxonomic identification of bats.

Exact inference for the risk ratio with an imperfect diagnostic test

The risk ratio quantifies the risk of disease in a study population relative to a reference population. Standard methods of estimation and testing assume a perfect diagnostic test having sensitivity and specificity of 100%. However, this assumption typically does not hold, and this may invalidate naive estimation and testing for the risk ratio. We propose procedures that control for sensitivity and specificity of the diagnostic test, given the risks are measured by proportions, as it is in cross-sectional studies or studies with fixed follow-up times. These procedures provide an exact unconditional test and confidence interval for the true risk ratio. The methods also cover the case when sensitivity and specificity differ in the two groups (differential misclassification). The resulting test and confidence interval may be useful in epidemiological studies as well as in clinical and vaccine trials. We illustrate the method with real-life examples which demonstrate that ignoring sensitivity and specificity of the diagnostic test may lead to considerable bias in the estimated risk ratio.

The wMel strain of Wolbachia Reduces Transmission of Zika virus by Aedes aegypti

Zika virus (ZIKV) is causing an explosive outbreak of febrile disease in the Americas. There are no effective antiviral therapies or licensed vaccines for this virus, and mosquito control strategies have not been adequate to contain the virus. A promising candidate for arbovirus control and prevention relies on the introduction of the intracellular bacterium Wolbachia into Aedes aegypti mosquitoes. This primarily has been proposed as a tool to control dengue virus (DENV) transmission; however, evidence suggests Wolbachia infections confer protection for Ae. aegypti against other arboviruses. At present, it is unknown whether or not ZIKV can infect, disseminate, and be transmitted by Wolbachia-infected Ae. aegypti. Using Ae. aegypti infected with the wMel strain of Wolbachia that are being released in Medellin, Colombia, we report that these mosquitoes have reduced vector competence for ZIKV. These results support the use of Wolbachia biocontrol as a multivalent strategy against Ae. aegypti-transmitted viruses.

The wMel Strain of Wolbachia Reduces Transmission of Chikungunya Virus in Aedes aegypti

Background

New approaches to preventing chikungunya virus (CHIKV) are needed because current methods are limited to controlling mosquito populations, and they have not prevented the invasion of this virus into new locales, nor have they been sufficient to control the virus upon arrival. A promising candidate for arbovirus control and prevention relies on the introduction of the intracellular bacterium Wolbachia into Aedes aegypti mosquitoes. This primarily has been proposed as a tool to control dengue virus (DENV) transmission; however, evidence suggests Wolbachia infections confer protection for Ae. aegypti against CHIKV. Although this approach holds much promise for limiting virus transmission, at present our understanding of the ability of CHIKV to infect, disseminate, and be transmitted by wMel-infected Ae. aegypti currently being used at Wolbachia release sites is limited.

Methodology/Principal Findings

Using Ae. aegypti infected with the wMel strain of Wolbachia that are being released in Medellin, Colombia, we report that these mosquitoes have reduced vector competence for CHIKV, even with extremely high viral titers in the bloodmeal. In addition, we examined the dynamics of CHIKV infection over the course of four to seven days post feeding. Wolbachia-infected mosquitoes remained non-infective over the duration of seven days, i.e., no infectious virus was detected in the saliva when exposed to bloodmeals of moderate viremia, but CHIKV-exposed, wild type mosquitoes did have viral loads in the saliva consistent with what has been reported elsewhere. Finally, the presence of wMel infection had no impact on the lifespan of mosquitoes as compared to wild type mosquitoes following CHIKV infection.

Conclusions/Significance

These results could have an impact on vector control strategies in areas where Ae. aegypti are transmitting both DENV and CHIKV; i.e., they argue for further exploration, both in the laboratory and the field, on the feasibility of expanding this technology beyond DENV.

New approaches to preventing chikungunya virus (CHIKV) infection are needed because the endemic range of this virus is expanding and because current methods are limited to controlling mosquito populations, and this approach has not effectively controlled this virus. A promising candidate for arbovirus control and prevention relies on the introduction of the intracellular bacterium Wolbachia into Aedes aegypti mosquitoes. Wolbachia biocontrol has advanced from laboratory experiments demonstrating that Wolbachia reduces virus replication to small-scale field trials demonstrating that Wolbachia are capable of spreading through wild Ae. aegypti populations. This primarily has been proposed as a tool to control dengue virus (DENV) transmission; however, Wolbachia infections confer protection for their insect hosts against a range of pathogens including CHIKV in Ae. aegypti. Medium-scale Wolbachia deployments are imminent or in certain instances have commenced. Therefore, assessing whether or not Wolbachia-infected Ae. aegypti are effective against CHIKV will help inform the viability of Wolbachia biocontrol for CHIKV control. Our study provides valuable evidence that could justify expanding this type of control program to other Ae. aegypti-transmitted arboviruses, primarily CHIKV.

Gastrointestinal helminths of wild hogs and their potential livestock and public health significance in Jamaica

An investigation into the potential for transmission of gastrointestinal helminths from wild hogs to livestock and humans was prompted by concerns of recreational wild-hog hunting in the Caribbean region and the recent practice, by livestock farmers in Jamaica, of co-rearing wild and domesticated swine. Thirty-one wild hogs from the Hellshire Hills, a dry limestone forest in southern Jamaica, were necropsied during the period June 2004 to August 2006. Thirteen of the captured animals were male and 18 female. Four species of adult helminths were recovered from the gastrointestinal tracts of the wild hogs: Hyostrongylus rubidus (77%), Globocephalus urosubulatus (48%), Oesophagostomum dentatum (42%) and Macroacanthorhynchus hirudinaceus (77%). Two (6.2%), ten (32.2%) and 18 (58.0%) hogs harboured one, two and three species of helminths, respectively. Mean infection intensities varied from 8.1 for M. hirudinaceus, to 115.5 for O. dentatum. There was no association between any of the recovered helminths and sex of the host; however, a multivariate analysis indicated a positive association between the prevalence of G. urosubulatus and host age (odds ratio (OR) = 6.517). Domesticated hogs co-reared with wild hogs are potentially at risk of infection with all four helminths, while wild-hog hunters and pig farmers may be exposed to M. hirudinaceus.

Role of biogenic amines in the post-mortem migration of Anisakis pegreffii (Nematoda: Anisakidae Dujardin, 1845) larvae into fish fillets

Infective third-stage larvae (L3) of nematode Anisakis spp. have been recognized as one of the major food-borne threats in lightly processed fish products in Europe, particularly in the Mediterranean region. Therefore, the effect of different storage temperatures of fish on larval post-mortem migration from visceral cavity into fillets is an important parameter to take into account when evaluating the risk for consumer safety. The European anchovy (Engraulis encrasicolus) were caught during fishing season, a subsample of fillets was checked for the presence of Anisakis larvae at capture (mean abundance=0.07), and the rest was stored at four different temperatures (-18, 0, 4 and 22°C) in order to count migrating larvae and measure the production of biogenic amines over a period of time. Larvae were identified by morphological features and molecular tools. Post-mortem migration was observed in fillets stored at 0 and 4°C after three and five days, respectively, but not at 22 and -18°C. In case of storage at 22°C for two days, at the onset of putrefaction of the visceral organs, larvae migrated out of the visceral cavity towards the fish surface. Measured pH and biogenic amine profile during storage indicated that certain biochemical conditions trigger larval migration into fillets. Likewise, migration was observed at pH ~6.4 when sensory degradation of the fish was markedly visible. Although larval migration was delayed for approximately four days at a temperature of <4°C the correlation between pH and abundance of A. pegreffii larvae in the fillet was high and statistically significant at both 0 (r=0.998, p<0.01) and 4°C (r=0.946, p<0.05). Out of eight biogenic amines measured, cadaverine and putrescine levels correlated the most with the post-mortem migration at 4°C, while tyramine levels were significant at both temperatures.

Exact meta-analysis approach for discrete data and its application to 2 × 2 tables with rare events

This paper proposes a general exact meta-analysis approach for synthesizing inferences from multiple studies of discrete data. The approach combines the p-value functions (also known as significance functions) associated with the exact tests from individual studies. It encompasses a broad class of exact meta-analysis methods, as it permits broad choices for the combining elements, such as tests used in individual studies, and any parameter of interest. The approach yields statements that explicitly account for the impact of individual studies on the overall inference, in terms of efficiency/power and the type I error rate. Those statements also give rises to empirical methods for further enhancing the combined inference. Although the proposed approach is for general discrete settings, for convenience, it is illustrated throughout using the setting of meta-analysis of multiple 2 × 2 tables. In the context of rare events data, such as observing few, zero or zero total (i.e., zero events in both arms) outcomes in binomial trials or 2 × 2 tables, most existing meta-analysis methods rely on the large-sample approximations which may yield invalid inference. The commonly used corrections to zero outcomes in rare events data, aiming to improve numerical performance can also incur undesirable consequences. The proposed approach applies readily to any rare event setting, including even the zero total event studies without any artificial correction. While debates continue on whether or how zero total event studies should be incorporated in meta-analysis, the proposed approach has the advantage of automatically including those studies and thus making use of all available data. Through numerical studies in rare events settings, the proposed exact approach is shown to be efficient and, generally, outperform commonly used meta-analysis methods, including Mental-Haenszel and Peto methods.

Three Anisakis spp. isolated from toothed whales stranded along the eastern Adriatic Sea coast

Knowledge concerning cetacean ecology in the Mediterranean is limited but important for sustainable planning and enforcement of appropriate conservation measures. Any information that might help to elucidate their ecology is essential. We explored the population and genetic structures of Anisakis spp. nematodes isolated from four toothed whale species - bottlenose dolphins (Tursiops truncatus), striped dolphins (Stenella coeruleoalba), Risso's dolphins (Grampus griseus) and Cuvier's beaked whales (Ziphius cavirostris) - stranded along the eastern Adriatic Sea coast (1990-2012) to reveal more information on host ecological patterns. Lower parasite prevalence was observed in resident dolphin species compared with occasionally occurring species, as well as in young compared with adult dolphins, indicating different feeding habits related to age. No unequivocal relationship between the biological traits of a host (age, body length, body mass and blubber depth) and Anisakis population parameters was observed. Phylogenetic analysis revealed a new geographical record of Anisakis simplex sensu stricto (1.96%) and Anisakis physeteris (1.31%) in the Adriatic Sea in addition to resident Anisakis pegreffii (96.73%). In an assessment of the Adriatic Sea and oceans worldwide, the genetic structure of Anisakis revealed that A. pegreffii populations do not differ among various final host species but do differ with respect to geographical location in contrast to previously accepted Anisakis panmixia.

Diversity of nematodes in the yellow-necked field mouse Apodemus flavicollis from the Peripannonic region of Serbia

Up to six nematode species were identified from 86 specimens of the yellow-necked field mouse Apodemus flavicollis from three mountainous localities known as Avala, Cer and Liškovac in Serbia. The highest prevalence of infection of 97% was recorded from Mt. Avala. Only one nematode species, Syphacia frederici, occurred in all three localities. There was complete overlap in nematode species from Mts. Avala and Liškovac, whereas the taxonomic distinctness of Mt. Cer was seen in the presence of the insect-transmitted species Rictularia proni. Locality was a statistically significant factor in all the best-fitted generalized linear models of variation in abundances. The highest level of both species richness and parasite alpha diversity (Shannon's H= 1.47) was found in the easternmost Mt. Liškovac, whereas the diversity indices were lowest for the westernmost Mt. Cer (Shannon's H= 0.48). In view of this geographical difference, the beta diversity indices were calculated along a west to east longitudinal gradient.

Sex-biased parasitism in Richardson’s ground squirrels (Urocitellus richardsonii) depends on the parasite examined

Sex-biased parasitism is found in many species, but the skew to one sex or the other varies and is most likely due to differences in host and parasite behaviour and the intensity of sexual selection. We examined sex-biased parasitism in Richardson’s ground squirrels (Urocitellus richardsonii (Sabine, 1822)) and hypothesized that males would be more heavily parasitized than females, as they are larger, have larger home ranges, and display high aggression and fighting during the short mating season, suggesting that they may trade off investment in immunity for higher investment in reproduction. Squirrels were caught during the mating season and examined for endoparasites and ectoparasites. Body mass, condition, and immune measures were recorded. Males had higher nematode prevalence and abundance, whereas females had higher flea prevalence. Males also had lower lymphocytes than females, as well as higher neutrophil to lymphocyte ratios. Females had higher eosinophils and they were in poorer body condition than males. The higher endoparasite loads in males suggests that they may be trading off immunity, whereas higher flea prevalence in females may be due to differences in sociality between the sexes. Our study demonstrates the importance of examining multiple parasite types to understand the factors influencing sex-biased parasitism.

Temperature during the free-living phase of an ectoparasite influences the emergence pattern of the infective phase

Understanding the population dynamics and co-evolution of host–parasite systems requires detailed knowledge of their phenology which, in turn, requires a deep knowledge of the effect of abiotic factors on the life cycles of organisms. Temperature is known to be a key environmental influence that participates in the regulation of diapause. Yet, not much is known about the effect of temperature on the free-living stages of true parasites and how it may influence host–parasite interactions. Here we experimentally study the effect of ambient temperature on overwintering pupae of Carnus hemapterus (Diptera, Carnidae), an ectoparasitic fly of various bird species. We also test whether chilling is a prerequisite for completion of diapause in this species. In the course of three winter seasons we experimentally exposed carnid pupae from nests of various host species to spring temperatures with and without chilling and recorded the emergence patterns in experimental and control groups. Experimental groups showed an advanced emergence date, a lower emergence rate and, consequently, a protracted emergence period. Chilling had no obvious effect on the start of emergence but it did advance the mean emergence date, shortened the length of the emergence period when compared with the control treatment and increased the emergence rate when compared with the spring treatment. This study identifies an environmental cue, namely temperature during the free-living stage, affecting the emergence of a widespread parasite and demonstrates the plasticity of diapause in this parasite. Our findings are of potential significance in understanding host–parasite interactions.

The functional importance of sequence versus expression variability of MHC alleles in parasite resistance

Understanding selection processes driving the pronounced allelic polymorphism of the major histocompatibility complex (MHC) genes and its functional associations to parasite load have been the focus of many recent wildlife studies. Two main selection scenarios are currently debated which explain the susceptibility or resistance to parasite infections either by the effects of (1) specific MHC alleles which are selected frequency-dependent in space and time or (2) a heterozygote or divergent allele advantage. So far, most studies have focused only on structural variance in co-evolutionary processes although this might not be the only trait subject to natural selection. In the present study, we analysed structural variance stretching from exon1 through exon3 of MHC class II DRB genes as well as genotypic expression variance in relation to the gastrointestinal helminth prevalence and infection intensity in wild yellow-necked mice (Apodemus flavicollis). We found support for the functional importance of specific alleles both on the sequence and expression level. By resampling a previously investigated study population we identified specific MHC alleles affected by temporal shifts in parasite pressure and recorded associated changes in allele frequencies. The allele Apfl-DRB*23 was associated with resistance to infections by the oxyurid nematode Syphacia stroma and at the same time with susceptibility to cestode infection intensity. In line with our expectation, MHC mRNA transcript levels tended to be higher in cestode-infected animals carrying the allele Apfl-DRB*23. However, no support for a heterozygote or divergent allele advantage on the sequence or expression level was detected. The individual amino acid distance of genotypes did not explain individual differences in parasite loads and the genetic distance had no effect on MHC genotype expression. For ongoing studies on the functional importance of expression variance in parasite resistance, allele-specific expression data would be preferable.

Molecular identification and population dynamic of Anisakis pegreffii (Nematoda: Anisakidae Dujardin, 1845) isolated from the European anchovy (Engraulis encrasicolus L.) in the Adriatic Sea

Anchovy Engraulis encrasicolus (L.) is a coastal pelagic and euryhaline species that represents the only European species of the family Engraulidae, with a widespread distribution. In Croatia, it is marketed fresh, frozen, salted or marinated and mainly exported to Italy and Spain, however Anisakis sp. larval infection is frequently the reason for border rejection. Since it is known that the prevalence and intensity of Anisakis infection varies with fish species, fishing area and season, the aim of our study was to identify Anisakis sp. parasitizing European anchovy and infer its population dynamic through a 2.5-year period. Larvae were found coiled and encysted on the external wall of intestine (94%) and reproductive organs (6%), rarely in fillets. Prevalence was 76.1% (95% confidence limits 74.51-77.56%), mean abundance 6.59 (bootstrap 95% confidence limits 5.81-7.26) and mean intensity 8.67 (bootstrap 95% confidence limits 7.82-9.35). The partial CO2 mitochondrial DNA sequence of the isolated anisakids confirmed clustering of the anchovy parasite within A. pegreffii sister group. Parasite population structure showed plasticity inferred by fishing ground, sampling year and fish gender and size. Compared to anisakid prevalence/abundance in other fish, the European anchovy in the Adriatic Sea represents a moderately high-infected paratenic host, although in the Mediterranean and Atlantic waters, anchovies have shown strikingly lesser values of prevalence. Since this host represents one of the most attractive Mediterranean fisheries products traditionally consumed without thermal preparation that in any case would not disrupt larval antigenicity and prevent human allergies, and given the high prevalence of the anisakid within the host, it is necessary to include anchovy into more firm risk assessment frames in order to develop measures that will support the safe alimentary production and consumption of seafood.

Mixed life-history strategies in a local population of the ectoparasitic fly Carnus hemapterus

A major issue for the proper understanding of the evolution of life-cycle histories is the regulation of voltinism and its variation. Diapause characteristics are known to regulate voltinism, but the underlying mechanisms are poorly understood. This paper studies diapause duration and voltinism variation in a haematophagous diptera parasitizing 2 sympatric hosts with very different breeding phenologies. We hypothesize that bivoltinism will be more frequent in carnid flies parasitizing an early breeding, multi-brooded species than in flies parasitizing a late breeder, single-brooded species. We obtained evidence of the co-occurrence of uni- and bivoltinism in both clutches of the multi-brooded Spotless starling (Sturnus unicolor) as well as in clutches of the single-brooded European roller (Coracias garrulus). Unexpectedly, the proportion of bivoltine flies was similar in both host species. A remarkable degree of host-parasite synchronization at the population level was found for bivoltine flies. Our findings reveal the facultative nature of diapause in Carnus. We discuss the influence of abiotic conditions and host availability on polymorphism in life-history cycles and the consequences both for the parasite and the host.

Filarial worms reduce Plasmodium infectivity in mosquitoes

BACKGROUND

Co-occurrence of malaria and filarial worm parasites has been reported, but little is known about the interaction between filarial worm and malaria parasites with the same Anopheles vector. Herein, we present data evaluating the interaction between Wuchereria bancrofti and Anopheles punctulatus in Papua New Guinea (PNG). Our field studies in PNG demonstrated that An. punctulatus utilizes the melanization immune response as a natural mechanism of filarial worm resistance against invading W. bancrofti microfilariae. We then conducted laboratory studies utilizing the mosquitoes Armigeres subalbatus and Aedes aegypti and the parasites Brugia malayi, Brugia pahangi, Dirofilaria immitis, and Plasmodium gallinaceum to evaluate the hypothesis that immune activation and/or development by filarial worms negatively impact Plasmodium development in co-infected mosquitoes. Ar. subalbatus used in this study are natural vectors of P. gallinaceum and B. pahangi and they are naturally refractory to B. malayi (melanization-based refractoriness).

METHODOLOGY/PRINCIPAL FINDINGS

Mosquitoes were dissected and Plasmodium development was analyzed six days after blood feeding on either P. gallinaceum alone or after taking a bloodmeal containing both P. gallinaceum and B. malayi or a bloodmeal containing both P. gallinaceum and B. pahangi. There was a significant reduction in the prevalence and mean intensity of Plasmodium infections in two species of mosquito that had dual infections as compared to those mosquitoes that were infected with Plasmodium alone, and was independent of whether the mosquito had a melanization immune response to the filarial worm or not. However, there was no reduction in Plasmodium development when filarial worms were present in the bloodmeal (D. immitis) but midgut penetration was absent, suggesting that factors associated with penetration of the midgut by filarial worms likely are responsible for the observed reduction in malaria parasite infections.

CONCLUSIONS/SIGNIFICANCE

These results could have an impact on vector infection and transmission dynamics in areas where Anopheles transmit both parasites, i.e., the elimination of filarial worms in a co-endemic locale could enhance malaria transmission.

Inferences about a linear combination of proportions

Statistical methods for carrying out asymptotic inferences (tests or confidence intervals) relative to one or two independent binomial proportions are very frequent. However, inferences about a linear combination of K independent proportions L = Σβipi (in which the first two are special cases) have had very little attention paid to them (focused exclusively on the classic Wald method). In this article the authors approach the problem from the more efficient viewpoint of the score method, which can be solved using a free programme, which is available from the webpage quoted in the article. In addition the article offers approximate formulas that are easy to calculate, gives a general proof of Agresti’s heuristic method (consisting of adding a certain number of successes and failures to the original results before applying Wald’s method) and, finally, it proves that the score method (which verifies the desirable properties of spatial and parametric convexity) is the best option in comparison with other methods.

Exact confidence limits for prevalence of a disease with an imperfect diagnostic test

Estimation of prevalence of disease, including construction of confidence intervals, is essential in surveys for screening as well as in monitoring disease status. In most analyses of survey data it is implicitly assumed that the diagnostic test has a sensitivity and specificity of 100%. However, this assumption is invalid in most cases. Furthermore, asymptotic methods using the normal distribution as an approximation of the true sampling distribution may not preserve the desired nominal confidence level. Here we proposed exact two-sided confidence intervals for the prevalence of disease, taking into account sensitivity and specificity of the diagnostic test. We illustrated the advantage of the methods with results of an extensive simulation study and real-life examples.