Mean Prevalence Of Infection Research Articles

First report of natural infection of Anopheles gambiae s.s. and Anopheles coluzzii by Wolbachia and Microsporidia in Benin: a cross-sectional study

BackgroundRecently, bacterial endosymbiont, including Wolbachia and Microsporidia were found to limit the infection of Anopheles mosquitoes with Plasmodium falciparum. This study aimed to investigate the natural presence of key transmission-blocking endosymbionts in Anopheles gambiae and Anopheles coluzzii in Southern Benin.MethodsThe present study was conducted in seven communes (Cotonou, Porto-Novo, Aguégués, Ifangni, Pobè Athiémé, and Grand-Popo) of Southern Benin. Anopheles were collected using indoor/outdoor Human Landing Catches (HLCs) and Pyrethrum Spray Catches (PSCs). Following morphological identification, PCR was used to identify An. gambiae sensu lato (s.l.) to species level and to screen for the presence of both Wolbachia and Microsporidia. Plasmodium falciparum sporozoite infection was also assessed using ELISA.ResultsOverall, species composition in An. gambiae s.l. was 53.7% An. coluzzii, while the remainder was An. gambiae sensu stricto (s.s.). Combined data of the two sampling techniques revealed a mean infection prevalence with Wolbachia of 5.1% (95% CI 0.90–18.6) and 1.3% (95% CI 0.07–7.8) in An. gambiae s.s. and An. coluzzii, respectively. The mean infection prevalence with Microsporidia was 41.0% (95% CI 25.9–57.8) for An. gambiae s.s. and 57.0% (95% CI 45.4–67.9) for An. coluzzii. Wolbachia was only observed in Ifangni, Pobè, and Cotonou, while Microsporidia was detected in all study communes. Aggregated data for HLCs and PSCs showed a sporozoite rate (SR) of 0.80% (95% CI 0.09–2.87) and 0.69% (95% CI 0.09–2.87) for An. gambiae and An. coluzzii, respectively, with a mean of 0.74% (95% CI 0.20–1.90). Of the four individual mosquitoes which harboured P. falciparum, none were also infected with Wolbachia and one contained Microsporidia.ConclusionsThe present study is the first report of natural infections of field-collected An. gambiae s.l. populations from Benin with Wolbachia and Microsporidia. Sustained efforts should be made to widen the spectrum of bacteria identified in mosquitoes, with the potential to develop endosymbiont-based control tools; such interventions could be the game-changer in the control of malaria and arboviral disease transmission.

Structural network characteristics affect epidemic severity and prediction in social contact networks

Understanding and mitigating epidemic spread in complex networks requires the measurement of structural network properties associated with epidemic risk. Classic measures of epidemic thresholds like the basic reproduction number (R0) have been adapted to account for the structure of social contact networks but still may be unable to capture epidemic potential relative to more recent measures based on spectral graph properties. Here, we explore the ability of R0 and the spectral radius of the social contact network to estimate epidemic susceptibility. To do so, we simulate epidemics on a series of constructed (small world, scale-free, and random networks) and a collection of over 700 empirical biological social contact networks. Further, we explore how other network properties are related to these two epidemic estimators (R0 and spectral radius) and mean infection prevalence in simulated epidemics. Overall, we find that network properties strongly influence epidemic dynamics and the subsequent utility of R0 and spectral radius as indicators of epidemic risk.

Seasonal patterns of Schistosoma mansoni infection within Biomphalaria snails at the Ugandan shorelines of Lake Albert and Lake Victoria.

Intestinal schistosomiasis is hyperendemic in many sub-Saharan African countries. In Uganda, it is endemic at both Lake Albert (LA) and Lake Victoria (LV) and caused by S. mansoni that uses Biomphalaria snails as obligatory intermediate snail hosts. To shed light on local patterns of infection, we utilised two PCR-based methods to detect S. mansoni within Biomphalaria spp. as collected at the Ugandan shorelines of Lake Albert and Lake Victoria from 2009-2010. Overall, at our Lake Albert sites, the mean infection prevalence was 12.5% (15 of 120 snails), while at our Lake Victoria sites the prevalence was 5% (3 of 60 snails). At our Lake Albert sites, the highest infection prevalence of 13.3% (8 of 60 snails) was at Walukuba, while at our Lake Victoria sites, the highest infection prevalence of 10% (2 of 20 snails) was at Lwanika. Three species of Biomphalaria, B. pfeifferi, B. stanleyi and B. sudanica, were identified at our Lake Albert collection sites, while only a single species, B. choanomphala, was identified at our Lake Victoria collection sites. Biomphalaria stanleyi (2 of 20 snails; 15%) had the highest infection prevalence, followed by B. sudanica (5 of 60 snails; 13.3%), B. pfeifferi (4 of 40 snails; 10%) and B. choanomphala (3 of 60 snails; 5%). Of the Biomphalaria species identified, B. choanomphala had the highest haplotype (gene) diversity score, followed by B. stanleyi, B. sudanica and B. pfeifferi. Sites with a higher mean prevalence of S. mansoni infection had higher intra-species haplotype diversity scores than sites with a lower mean prevalence. The wet seasons (LA: 13.3%; LV: 8.7%) had a consistently higher mean infection prevalence of S. mansoni than the dry seasons (LA: 9.5%; LV: 5%) for all species and all sites tested at both Lake Albert (n = 480) and Lake Victoria (n = 320), though the difference was not statistically significant.

Urogenital schistosomiasis among pre-school and school aged children in four districts of north western Tanzania after 15 years of mass drug administration: Geographical prevalence, risk factors and performance of haematuria reagent strips.

Urogenital schistosomiasis remains as a public health problem in Tanzania and for the past 15 years, mass drug administration (MDA) targeting primary school children has remained as the mainstay for its control. However, after multiple rounds of MDA in highly risk groups, there are no data on the current status of Schistosoma haematobium in known endemic areas. Furthermore, the performance of commonly used diagnostic test, the urine reagent strips is not known after the decline in prevalence and intensities of infection following repeated rounds of treatment. Thus, after 15 of national MDA, there is a need to review the strategy and infection diagnostic tools available to inform the next stage of schistosomiasis control in the country. A analytical cross-sectional study was conducted between October and November, 2019 among pre-school (3-5years old) and school aged children (6-17 years old) living in four (4) districts with low (<10%) and moderate (10%-<50%) endemicity for schistosomiasis as per WHO classification at the start of the national control programme in 2005/06, with mean prevalence of 20.7%. A total of 20,389 children from 88 randomly selected primary schools participated in the study. A questionnaire was used to record demographic information. A single urine sample was obtained from each participant and visually examined for macrohaematuria, tested with a dipstick for micro-haematuria, to determine blood in urine; a marker of schistosome related morbidity and a proxy of infection. Infection intensity was determined by parasitological examination of the urine sample for S. haematobium eggs. Overall, mean infection prevalence was 7.4% (95%CI: 7.0-7.7, 1514/20,389) and geometric mean infection intensity was 15.8eggs/10mls. Both infection prevalence (5.9% versus 9%, P<0.001) and intensity (t = -6.9256, P<0.001) were significantly higher in males compared to females respectively. Light and heavy infections were detected in 82.3% and 17.7% of the positive children respectively. The prevalence of macrohaematuria was 0.3% and that of microhaematuria was 9.3% (95%CI:8.9-9.7). The sensitivity and specificity of the urine reagent strip were 78% (95%CI: 76.1-79.9) and 99.8% (95%CI: 99.7-99.9). Having light (P<0.001) and heavy infection intensities (P<0.001) and living in the study districts increased the odd of having microhaematuria. Predictors of S. haematobium infection were being male (P<0.003), microhaematuria (P<0.001), and living in the three study districts (P<0.001) compared to living at Nzega district. The findings provide an updated geographical prevalence which gives an insight on the planning and implementation of MDA. Comparing with the earlier mapping survey at the start of the national wide mass drug administration, the prevalence of S. haematobium infection have significantly declined. This partly could be attributed to repeated rounds of mass drug administration. The urine reagent strips remain as a useful adjunct diagnostic test for rapid monitoring of urogenital schistosomiasis in areas with low and high prevalence. Based on prevalence levels and with some schools having no detectable infections, review of the current blanket mass drug administration is recommended.

Bithyniid snails as hosts of Opisthorchiidae and Notocotylidae in the south of Western Siberia, Russia.

Opisthorchiasis and related infections are persistent and substantial public health burdens from eastern Europe to southeastern and northern Asia. Snails of the family Bithyniidae act as first intermediate hosts not only for the trematodes of the family Opisthorchiidae but also for those of the family Notocotylidae. There are certain morphological similarities between the aforementioned trematode cercariae. In order to find natural local foci of opisthorchiasis, which are established primarily according to the presence of infected bithyniid snails at the area under examination, it is crucial to correctly identify the rediae and cercariae of the trematodes. The aim of our investigation was to evaluate the role of bithyniid snails in the transmission of Opisthorchiidae and Notocotylidae in ecosystems in the south of Western Siberia. We have been studying the process of bithyniid snail dissemination in Western Siberia and examining their infection by trematodes from 1994 until now. A total of 16,213 bithyniid snails in 23 water bodies (in 28 localities) of four major basins situated in the Novosibirsk region were inspected for trematode infestation. Long-term research has been conducted in the Kargat river estuary and the Ob river floodplain for 15 and 25years, respectively. In both water bodies, the prevalence of notocotylid and opisthorchiid trematodes was positively correlated with the global land-ocean temperature index. Trematode parthenitae were identified if there were mature cercariae capable of leaving the shell of the host snail on their own. Identification to the species of opisthorchiid cercariae was verified using molecular genetic analysis methods targeting ITS2 locus. Opisthorchis felineus and Metorchis bilis, two opisthorchiid species that are potentially perilous to human health, were found in bithyniids in the Novosibirsk region. The mean prevalence of infection with notocotylid trematodes in bithyniid snails was higher than the corresponding prevalence of infection with opisthorchiid trematodes. The results of this study can be used to identify and predict natural foci of epidemiologically and/or epizootically dangerous diseases.

Prevalence of Anaplasma phagocytophilum in questing Ixodes ricinus nymphs across twenty recreational areas in England and Wales

Human granulocytic anaplasmosis and tick-borne fever, affecting livestock, are diseases caused by an infection with the bacterium Anaplasma phagocytophilum. Its transmission dynamics between vertebrate hosts and ticks remain largely unknown and the potential impact on public health in the United Kingdom is unclear. This study aimed to assess the distribution and estimate the prevalence of A. phagocytophilum in questing Ixodes ricinus at recreational locations across England and Wales over six years. An additional objective was to investigate possible associations between prevalence, habitat and presence of ruminant hosts. Ixodes ricinus ticks were collected each spring at 20 recreational locations across England and Wales between 2014 and 2019. Nymphs were tested for infection with A. phagocytophilum by detection of bacterial genome in DNA extracts, targeting the msp2 gene locus. Positive samples were further investigated for the presence of different ecotypes based on the GroEL region. Of 3,919 nymphs tested, the mean infection prevalence was 3.6% [95%CI: 3.1-4.3] and ranged from 0 to 20.4%. Northern England had a higher overall prevalence (4.7% [95%CI: 3.4-6.4]) compared to Southern England (1.8% [95%CI: 1.3-2.5]) and the presence of sheep was associated with higher A. phagocytophilum prevalence (8.4% [95%CI: 6.9-10.1] vs 1.2% [95%CI: 0.8-1.7] when absent). There was also a negative correlation with the prevalence of Borrelia burgdorferi s.l. (causing Lyme borreliosis). When investigating the diversity of A. phagocytophilum, ecotype I accounted for 86.8% of samples and ecotype II for 13.2%. Our study presents an overview of A. phagocytophilum prevalence in questing I. ricinus in recreational areas across England and Wales and discusses the potential public and veterinary health relevance.

Seasonal patterns and spatial variation of Borrelia burgdorferi (sensu lato) infections in Ixodes ricinus in the Netherlands

BackgroundThe incidence of Lyme borreliosis varies over time and space through as yet incompletely understood mechanisms. In Europe, Lyme borreliosis is caused by infection with a Borrelia burgdorferi (s.l.) genospecies, which is primarily transmitted by a bite of Ixodes ricinus nymphs. The aim of this study was to investigate the spatial and temporal variation in nymphal infection prevalence of B. burgdorferi (s.l.) (NIP), density of questing nymphs (DON) and the resulting density of infected nymphs (DIN).MethodsWe investigated the infection rates in I. ricinus nymphs that were collected monthly between 2009 and 2016 in 12 locations in the Netherlands. Using generalized linear mixed models, we explored how the NIP, DON and DIN varied during the seasons, between years and between locations. We also determined the genospecies of the Borrelia infections and investigated whether the genospecies composition differed between locations.ResultsThe overall NIP was 14.7%. A seasonal pattern in infection prevalence was observed, with higher estimated prevalences in the summer than in the spring and autumn. This, combined with higher nymphal densities in summer, resulted in a pronounced summer peak in the estimated DIN. Over the 7.5-year study period, a significant decrease in infection prevalence was found, as well as a significant increase in nymphal density. These two effects appear to cancel each other out; the density of infected nymphs, which is the product of NIP × DON, showed no significant trend over years. Mean infection prevalence (NIP, averaged over all years and all months) varied considerably between locations, ranging from 5 to 26%. Borrelia genospecies composition differed between locations: in some locations almost all infections consisted of B. afzelii, whereas other locations had more diverse genospecies compositions.ConclusionIn the Netherlands, the summer peak in DIN is a result of peaks in both NIP and DON. No significant trend in DIN was observed over the years of the study, and variations in DIN between locations were mostly a result of the variation in DON. There were considerable differences in acarological risk between areas in terms of infection prevalence and densities of ticks as well as in Borrelia genospecies composition.Graphical

Prevalence and risk factors of geohelminthiasis among the rural village children in Kota Marudu, Sabah, Malaysia.

Geohelminthiasis is a worldwide problem, especially in low-income countries. Children from rural areas and those living in poverty, lacking basic health amenities and having poor environmental sanitation are likely to be affected. Adverse effects such as anemia, protein malnutrition, colitis are common which can affect both the children's physical and mental growing development. A cross-sectional study on geohelminthiasis was conducted among children from 238 households in 13 villages in Kota Marudu of northern Sabah, East Malaysia. The study involved interviewing villagers using questionnaires to collect demographic and socio-economic data, getting faecal samples from the children, collecting soil samples and identifying parasite eggs with microscopy and molecular methods. A total of 407 children (6 months-17 years old) enrolled in the study. Geohelminthiasis was detected in the faecal samples of children from 54% (7/13) of the villages with mean prevalence of infection per village of 9.0% (0%-34.9%). On a household basis, 18% (43/238) of the households sampled had infected children, with mean prevalence rate per household of 11% (0%-43%). The prevalence was for Ascaris lumbricoides: 9.6% (39/407), Trichuris trichiura: 2.7% (11/407) and hookworms (Necator americanus and Ancylostoma sp.): 2.7% (11/407). The overall mean infection rate of the children examined was 14.3%. Significantly higher prevalence was recorded for the children of mothers who did not have any formal education (p = 0.003); household income of less than USD119 (RM500) (p<0.001); children from homes without proper sanitation facilities (p<0.001); children who usually go about barefoot (p<0.001) and not washing feet before entering the house (p = 0.017). Soil samples were found to have geohelminth eggs or larvae which could be due to unhygienic sanitation practices. This study shows the geohelminthiasis is prevalent in the villages, and the risk factors are lack of maternal education, low income, poor sanitation facilities and irregular deworming practice. Expanding deworming coverage in the study region may help reduce the worm infections in these communities, so that the mental and physical development of the children would not be affected by geohelminthiasis. The data on the prevalence of geohelminthiasis in this study would contribute to better public health monitoring and operation to reduce the infection in rural areas.

Prevalence of the nematodes Eustrongylides exisus Jägerskiöld, 1909, – larvae (Nematoda: Dioctophymatidae) infection in the Rutilis rutilis, linnaeus 1758 and the seasonal dynamics of the infection in the waters of the Dnipro-Buh estuari in southern Ukrai

In this study, we determined the prevalence and seasonal dynamic of the infection of the Rutilis rutilis, Lіnnaeus 1758 with the nematode Eustrongylides excisus. The fish was caught in the waters of the Dnipro-Buh estuary in seven sample collection sites between 2016 and 2019. They all underwent ichthyopathological examination. Parasites, found during examination, undergone microscopy to determine their taxonomy. Overall 595 specimens were obtained. The mean prevalence of infection over entire study period (2016–2019) was 17.4 %. Ichthyopathological examination of the roach caught in the waters of the Dnipro-Buh estuary revealed the infection with larvae E. excises nematode. The parasitic larvae were found in the muscles of the ventral abdominal wall of the roach. There was more than two-fold difference in the prevalence of infection between sample collection sites – from 12 % in site 5 near Sofiivka to 28 % in site 3 near the village Oleksandrivka over the study period in 2016–2019. The total prevalence of infection in roaches in the Dnipro-Buh estuary was 17.4 %. Seasonal changes were not statistically significant and ranged from 12.8 % in summer to 20.1 % in spring. Annual changes suggested a possible upward trend, but more observations are needed to confirm it. Аnnual changes were not statistically significant. The prevalence of infection changed throughout the year: there were two peaks in spring (20.1 %) and autumn (18.3 %). In summer (12.8 %) and winter (15.1 %) the prevalence of infection was lower. Morphologically, the E. excisus larvae found in roaches were different compared to those found in predatory fishes: they had more pale color and were smaller in length. E. excisus is a prevalent infection of roach in Dnipro-Buh estuary. Considering seemingly increasing prevalence of E.excisus infection, further studies are required to understand a pathophysiology of E.excisus infection in mammals and humans, since data remain limited.

Preliminary Assessment of Gastrointestinal Parasites in Two Wild Groups of Endangered Moor Macaques (Macaca maura) from Sulawesi

Information on parasite biodiversity and abundance can improve our understanding of parasitic infections on endangered wildlife, as parasites can affect host survival and reproduction and may play a crucial role in determining population dynamics. We conducted a noninvasive assessment of gastrointestinal parasites in wild Macaca maura, an Endangered primate endemic to the Indonesian island of Sulawesi and examined the influence of season and sex on parasite richness and prevalence. We collected fecal samples (N = 72) from 18 individuals from two groups. We collected data from September 2014 to February 2015 and from June to November 2016, sampling each individual at least twice. We detected two taxa of nematodes (Trichuris sp. and Strongylida fam. gen.) and eight of protozoa (Giardia duodenalis, Chilomastix mesnili, Entamoeba hartmanni, Entamoeba polecki-like, Entamoeba coli, Iodamoeba butschlii, Balantoides coli, and Blastocystis sp.). The gastrointestinal parasite richness (2.5 ± 0.4 SD) was below the mean reported for nonthreatened primates, whereas the mean prevalence of infection across all parasites (56.3%) was above the mean. We did not find any statistically significant difference in parasite richness or prevalence between seasons or the sexes. This preliminary assessment addresses the paucity of studies on parasites of wild primates in Southeast Asia and can contribute to our understanding of the newly emerging human–macaque interface at this site.

Negative effects of parasitic lung nematodes on the fitness of a Neotropical toad (Rhinella horribilis).

Pathogens are increasingly implicated in amphibian declines but less is known about parasites and the role they play. We focused on a genus of nematodes (Rhabdias) that is widespread in amphibians and examined their genetic diversity, abundance (prevalence and intensity), and impact in a common toad (Rhinella horribilis) in Panama. Our molecular data show that toads were infected by at least four lineages of Rhabdias, most likely Rhabdias pseudosphaerocephala, and multiple lineages were present in the same geographic locality, the same host and even the same lung. Mean prevalence of infection per site was 63% and mean intensity of infection was 31 worms. There was a significant effect of host size on infection status in the wild: larger toads were more likely to be infected than were smaller conspecifics. Our experimental infections showed that toadlets that were penetrated by many infective Rhabdias larvae grew less than those who were penetrated by few larvae. Exposure to Rhabdias reduced toadlet locomotor performance (both sustained speed and endurance) but did not influence toadlet survival. The effects of Rhabdias infection on their host appear to be primarily sublethal, however, dose-dependent reduction in growth and an overall impaired locomotor performance still represents a significant reduction in host fitness.

The species diversity of ticks that attack human hosts in Eastern Siberia (Russian Federation) and prevalence of tick-borne pathogens

Purpose: The purpose of this work was to characterize the population of ticks that attack humans in the Eastern Siberia and analyze the dynamics of tick-borne infections in the region. Methods & Materials: Ticks were delivered to the laboratory by bitten people between 25.03.2007 and 17.10.2017. The developmental stage and species of ticks were identified morphologically using appropriate key guides. Four tick-borne pathogens, i.e. tick-borne encephalitis virus (TBEV), Borrelia burgdorferi sensu lato, Anaplasma phagocytophylum, Ehrlichia muris\E. chaffeensis were detected in ticks using the range of laboratory diagnostic metods, including direct ligth microscopy, ELISA and real-time PCR. Results: Total of 46357 tick specimens detached from bitten people were identified and tested individually during 10 consecutive years. The majority (85,4%) of victims was bitten by I. persulcatus; 14,55% of attacks on humans were caused by D. nuttalli and D. silvarum; whereas H. concinna was documented only in 25 cases (0.05%). Among all studied ticks, several unconventional species i.e. Rhipicephalus sanguineus, D. reticulatus and Amblyomma americanum were identified. In 2017, besides two cases of R. sanguineus bites, the bite of A. testudinarium was registered. Analysis of tick bite histories indicates that five cases have local origin whereas other five ticks are inported from endemic regions. Mean prevalence of infection in I. persulcatus comprised 12 ± 6,5%, 7,8 ± 2,7%, 4,6 ± 1,5% and 1 ± 0,7% for B. burgdorferi sensu lato, A. phagocytophylum, Ehrlichia sp. and TBEV respectively. The dynamics of the prevalence of TBEV and B. burgdorferi s.l. in I. persulcatus indicate the significant increase of infection rate during 2014 – 2017. In Dermacentor sp., the prevalence of every infection was below 5%, with the highest rate for A. phagocytophilum (4,2 ± 3,7%). No pathogens detected in H. concinna. Conclusion: I. persulcatus remains the most important vector of tick-borne diseases to humans in Eastern Siberia with highest attack rate and with about 25% of ticks being infected with at least one of four pathogens. The H. concinna does not play any significant role as a disease vector. The regular events of invasion of non-endmic tick species are discovered.

Periodic, Parasite-Mediated Selection For and Against Sex.

Asexual lineages should rapidly replace sexual populations. Why sex then? The Red Queen hypothesis proposes that parasite-mediated selection against common host genotypes could counteract the per capita birth rate advantage of asexuals. Under the Red Queen hypothesis, fluctuations in parasite-mediated selection can drive fluctuations in the asexual population, leading to the coexistence of sexual and asexual reproduction. Does shifting selection by parasites drive fluctuations in the fitness and frequency of asexuals in nature? Combining long-term field data with mesocosm experiments, we detected a shift in the direction of parasite selection in the snail Potamopyrgus antipodarum and its coevolving parasite, Microphallus sp. In the early 2000s, asexuals were more infected than sexuals. A decade later, the asexuals had declined in frequency and were less infected than sexuals. Over time, the mean infection prevalence of asexuals equaled that of sexuals but varied far more. This variation in asexual infection prevalence suggests the potential for parasite-mediated fluctuations in asexual fitness. Accordingly, we detected fitness consequences of the shift in parasite selection: when they were less infected than sexuals, asexuals increased in frequency in the field and in paired mesocosms that isolated the effect of parasites. The match between field and experiment argues that coevolving parasites drive temporal change in the relative fitness and frequency of asexuals, potentially promoting the coexistence of reproductive modes in P. antipodarum.

Mass azithromycin distribution for hyperendemic trachoma following a cluster-randomized trial: A continuation study of randomly reassigned subclusters (TANA II).

BackgroundThe World Health Organization recommends annual mass azithromycin administration in communities with at least 10% prevalence of trachomatous inflammation–follicular (TF) in children, with further treatment depending on reassessment after 3–5 years. However, the effect of stopping mass azithromycin distribution after multiple rounds of treatment is not well understood. Here, we report the results of a cluster-randomized trial where communities that had received 4 years of treatments were then randomized to continuation or discontinuation of treatment.Methods and findingsIn all, 48 communities with 3,938 children aged 0–9 years at baseline in northern Ethiopia had received 4 years of annual or twice yearly mass azithromycin distribution as part of the TANA I trial. We randomized these communities to either continuation or discontinuation of treatment. Individuals in the communities in the continuation arm were offered either annual or twice yearly distribution of a single directly observed dose of oral azithromycin. The primary outcome was community prevalence of ocular chlamydial infection in a random sample of children aged 0–9 years, 36 months after baseline. We also assessed the change from baseline to 36 months in ocular chlamydia prevalence within each arm. We compared 36-month ocular chlamydia prevalence in communities randomized to continuation versus discontinuation in a model adjusting for baseline ocular chlamydia prevalence. A secondary prespecified analysis assessed the rate of change over time in ocular chlamydia prevalence between arms. In the continuation arm, mean antibiotic coverage was greater than 90% at all time points. In the discontinuation arm, the mean prevalence of infection in children aged 0–9 years increased from 8.3% (95% CI 4.2% to 12.4%) at 0 months to 14.7% (95% CI 8.7% to 20.8%, P = 0.04) at 36 months. Ocular chlamydia prevalence in communities where mass azithromycin distribution was continued was 7.2% (95% CI 3.3% to 11.0%) at baseline and 6.6% (95% CI 1.1% to 12.0%, P = 0.64) at 36 months. The 36-month prevalence of ocular chlamydia was significantly lower in communities continuing treatment compared with those discontinuing treatment (P = 0.03). Limitations of the study include uncertain generalizability outside of trachoma hyperendemic regions.ConclusionsIn this study, ocular chlamydia infection rebounded after 4 years of periodic mass azithromycin distribution. Continued distributions did not completely eliminate infection in all communities or meet WHO control goals, although they did prevent resurgence.Trial registrationThis study was prospectively registered at clinicaltrials.gov (clinicaltrials.gov NCT01202331).

Oomycete parasites in freshwater copepods of Patagonia: effects on survival and recruitment.

Copepods are hosts to various oomycete parasite species, but the effects of pathogens on copepod populations have rarely been studied. This study aimed to characterize oomycete infection in the freshwater copepod Parabroteas sarsi in a temporary pond in Patagonia (Argentina). A complete hydroperiod was monitored, evaluating environmental variables as influencing factors in the oomycete infections. Laboratory experiments were performed to evaluate the susceptibility of infected copepods to consumption by predators. Although 5 species of copepods were present in the pond, only ovigerous P. sarsi females were parasitized by oomycetes. Two species of oomycetes were always found together: Aphanomyces ovidestruens and Pythium flevoense. Infections were detected at water temperatures >20°C, with a positive relationship between temperature and parasite prevalence. Infection occurred after a decrease in large filter-feeder densities. The pathogens were not lethal to P. sarsi females in the short-term, but did produce mortality of entire egg sacs, thus negatively impacting subsequent recruitment. Mean prevalence of infection in females was 53%, reaching 83% in December. Females have the capacity to release an infected egg sac and generate a new one in a few days. This infection does not affect the susceptibility of P. sarsi to the predator Notonecta vereertbruggheni. The decrease in female abundance registered towards the end of the hydroperiod could be related to a combination of factors that may have a differential effect on female survival, such as increasing temperature, the energy cost of egg sac development and carrying and oomycete infection.

Distribution of Trematodes Cryptokotyle (Trematoda, Heterophyidae), in Fish of the Family Gobiidae in the Estuary Waters and the Black Sea in Southern Ukraine

Abstract The article describes occurrence and distribution of Cryptocotyle trematodes in fish in the waters of the Dnipro-Buh estuary and the Black Sea in Mykolaiv and Odesa Region. Study was conducted in 2015-2016. Two trematode species were found in natural waters of these regions: Cryptocotyle cancavum Crepli, 1825 and Cryptocotyle jejuna Nicoll, 1907. Th e latter species has not been previously registered in this region in southern Ukraine. Varying intensity of infection with Cryptocotyle metacercariae was observed in fish of Gobiidae family: Mesogobius batrachocephalus Pallas, 1814, Neogobius melanostomum Pallas, 1814, N. fluviatialis Pallas, 1814. Th e most affected species was N. melanostomum, with the prevalence of infection 59.2 %. Less infected were N. fluviatialis and M. batrachocephalus, with the prevalence of infection 30.4 % and 17 % respectively. The intensity of infection was the highest in N. melanostomum - 211 metacercariae per fish, followed by N. fluviatialis and M. batrachocephalu - 124 and 89 metacercariae respectively. Cryptocotyle was the most prevalent in the Dnipro-Buh estuary (cape Adzhigol, Mykolaiv Region) and much less prevalent in the waters of the Black Sea in Mykolaiv and Odesa Regions. Mean prevalence of infection was 31.4 %.

Heterogeneous network epidemics: real-time growth, variance and extinction of infection

Recent years have seen a large amount of interest in epidemics on networks as a way of representing the complex structure of contacts capable of spreading infections through the modern human population. The configuration model is a popular choice in theoretical studies since it combines the ability to specify the distribution of the number of contacts (degree) with analytical tractability. Here we consider the early real-time behaviour of the Markovian SIR epidemic model on a configuration model network using a multitype branching process. We find closed-form analytic expressions for the mean and variance of the number of infectious individuals as a function of time and the degree of the initially infected individual(s), and write down a system of differential equations for the probability of extinction by time t that are numerically fast compared to Monte Carlo simulation. We show that these quantities are all sensitive to the degree distribution—in particular we confirm that the mean prevalence of infection depends on the first two moments of the degree distribution and the variance in prevalence depends on the first three moments of the degree distribution. In contrast to most existing analytic approaches, the accuracy of these results does not depend on having a large number of infectious individuals, meaning that in the large population limit they would be asymptotically exact even for one initial infectious individual.

Fine-Scale Spatial Covariation between Infection Prevalence and Susceptibility in a Natural Population.

The prevalence of infection varies dramatically on a fine spatial scale. Many evolutionary hypotheses are founded on the assumption that this variation is due to host genetics, such that sites with a high frequency of alleles conferring susceptibility are associated with higher infection prevalence. This assumption is largely untested and may be compromised at finer spatial scales where gene flow between sites is high. We put this assumption to the test in a natural snail-trematode interaction in which host susceptibility is known to have a strong genetic basis. A decade of field sampling revealed substantial spatial variation in infection prevalence between 13 sites around a small lake. Laboratory assays replicated over 3 years demonstrate striking variation in host susceptibility among sites in spite of high levels of gene flow between sites. We find that mean susceptibility can explain more than one-third of the observed variation in mean infection prevalence among sites. We estimate that variation in susceptibility and exposure together can explain the majority of variation in prevalence. Overall, our findings in this natural host-parasite system argue that spatial variation in infection prevalence covaries strongly with variation in the distribution of genetically based susceptibility, even at a fine spatial scale.

Assessment of prevalence and distribution of spotted fever group rickettsiae in Manitoba, Canada, in the American dog tick, Dermacentor variabilis (Acari: Ixodidae).

Little is known about the distribution and prevalence of the spotted fever group rickettsiae in Canada. We conducted active surveillance for tick-associated rickettsiae in 10 localities in Manitoba. A total of 1044 adult American dog ticks, Dermacentor variabilis (Acari: Ixodidae), were collected and screened for spotted fever group rickettsiae. Rickettsia montanensis was the only species of rickettsia detected. The mean prevalence of infection was 9.8% (range, 0.00-21.74% among localities). The proportion of infected male and female ticks was not significantly different; however, tick populations near the northern limit of D. variabilis distribution in Manitoba had a lower prevalence of infection compared to tick populations from more southern localities in the province.

Structural and molecular characterization of Kudoa quraishii n. sp. from the trunk muscle of the Indian mackerel Rastrelliger kanagurta (Perciforme, Scombridae) in Saudi Arabia coasts

A new Myxozoa, Kudoa quraishii n. sp., is reported in the striated muscle of the Indian mackerel Rastrelliger kanagurta from the Red Sea and the Arabian Gulf in Saudi Arabia. Mean prevalence of infection is about 20% and varies between localities. The parasite develops whitish and oval or rounded pseudocysts of 0.2-3 mm in the striated muscles of the body. Pseudocysts are filled with mature spores. Myxospores are quadrate in shape in apical view with rounded edges and ovoid in side view. Each spore is formed by four equal shell valves and four symmetrical polar capsules. Polar capsules are pyriform in apical view and drop-like in side view. Myxospore measurements in micrometers are 6.14 (5.9-6.34) in width, 5.48 (5.3-5.71) in thickness, and 4.27 (4.1-4.42) in length. Polar capsule measurements in apical view in micrometers are 2.08 (1.88-2.28) and 1.31 (1.10-1.52) length by width. Molecular analysis based on SSU rDNA gene shows closest association with K. amamiensis and K. kenti with respectively 98 and 97.2% of similarities.