Endemic Cycles Research Articles

Hepatozoon canis in German red foxes (Vulpes vulpes) and their ticks: molecular characterization and the phylogenetic relationship to other Hepatozoon spp.

In this study, the prevalence of Hepatozoon spp. in red foxes (Vulpes vulpes) and their ticks from Germany, as well as molecular characterizations and phylogenetic relationship to other Hepatozoon spp. were investigated. DNA extracts of 261 spleen samples and 1,953 ticks were examined for the presence of Hepatozoon spp. by a conventional polymerase chain reaction (PCR) targeting the 18S rRNA gene. The ticks included four tick species: Ixodes ricinus, Ixodes canisuga, Ixodes hexagonus and Dermacentor reticulatus. A total of 118/261 foxes (45.2%) and 148/1,953 ticks (7.5%) were Hepatozoon PCR-positive. Amplicons from 36 positive foxes and 41 positive ticks were sequenced. All sequences obtained from foxes and 39/41 from ticks had a 99% similarity to Hepatozoon canis, whereas two ticks' sequences had a 99% identity to Hepatozoon sp. The obtained Hepatozoon sequences in this study were phylogenetically related to other Hepatozoon sequences detected in other countries, which may represent strain variants. The high prevalence of H. canis DNA in red foxes in this study supports the suggested role of those animals in distribution of this parasite. Furthermore, detection of DNA of H. canis in foxes and all examined tick species collected from those foxes allows speculating about previously undescribed potential vectors for H. canis and suggests a potential role of the red fox in its natural endemic cycles.

A molecular survey of Babesia spp. and Theileria spp. in red foxes (Vulpes vulpes) and their ticks from Thuringia, Germany

Wild canines which are closely related to dogs constitute a potential reservoir for haemoparasites by both hosting tick species that infest dogs and harbouring tick-transmitted canine haemoparasites. In this study, the prevalence of Babesia spp. and Theileria spp. was investigated in German red foxes (Vulpes vulpes) and their ticks.DNA extracts of 261 spleen samples and 1953 ticks included 4 tick species: Ixodes ricinus (n=870), I. canisuga (n=585), I. hexagonus (n=485), and Dermacentor reticulatus (n=13) were examined for the presence of Babesia/Theileria spp. by a conventional PCR targeting the 18S rRNA gene.One hundred twenty-one out of 261 foxes (46.4%) were PCR-positive. Out of them, 44 samples were sequenced, and all sequences had 100% similarity to Theileria annae. Similarly, sequencing was carried out for 65 out of 118 PCR-positive ticks. Theileria annae DNA was detected in 61.5% of the sequenced samples, Babesia microti DNA was found in 9.2%, and Babesia venatorum in 7.6% of the sequenced samples. The foxes were most positive in June and October, whereas the peak of tick positivity was in October. Furthermore, the positivity of the ticks was higher for I. canisuga in comparison to the other tick species and for nymphs in comparison to adults.The high prevalence of T. annae DNA in red foxes in this study suggests a reservoir function of those animals for T. annae. To our knowledge, this is the first report of T. annae in foxes from Germany as well as the first detection of T. annae and B. microti in the fox tick I. canisuga.Detection of DNA of T. annae and B. microti in three tick species collected from foxes adds new potential vectors for these two pathogens and suggests a potential role of the red fox in their natural endemic cycles.

First molecular assessment of the African swine fever virus status of Ornithodoros ticks from Swaziland.

African swine fever (ASF) is an economically significant haemorrhagic disease of domestic pigs. It is caused by the African swine fever virus (ASFV), a deoxyribonucleic acid (DNA)arbovirus. Argasid ticks of the genus Ornithodoros, which are widely distributed throughout southern Africa, play a primary role in virus maintenance and spread within the endemic sylvatic cycle. The ASF status of Swaziland is unknown, but this land-locked country is surrounded by ASF-positive countries, has a burgeoning pig industry and sylvatic cycle hosts present within its borders. In this first assessment of ASF status, warthog burrows in seven nature reserves and game management areas in Swaziland were investigated for tick and virus presence. Tick infestation rates of between 33.3% - 88.8% were recovered for the four Ornithodoros-infested reserves. A total of 562 ticks were screened for virus genome presence using a duplex Polymerase Chain Reaction (PCR) that targets the C-terminal end of the p72 gene of the ASFV and confirms DNA integrity through amplification of the 16S rRNA tick host gene. All samples were negative for virus genome presence and positive for the tick genome target. Nucleotide sequencing of the latter confirmed that Ornithodoros ticks from Swaziland are identical to those from the Kruger National Park in South Africa across the gene region characterised. Whilst this first evaluation of ASF presence in Swaziland indicates that the virus does not appear to be present in the key virus vector, the presence of sylvatic cycle hosts, together with the country's proximity to ASF-affected countries calls for expanded investigations and regular monitoring of the ASF status of Swaziland.

Range expansion of <em> Ixodes scapularis</em> ticks and of <em> Borrelia burgdorferi</em> by migratory birds

Recent studies have suggested that the risk of exposure to Lyme disease is emerging in Canada because of the expanding range of I. scapularis ticks. The wide geographic breeding range of I. scapularis-carrying migratory birds is consistent with the widespread geographical occurrence of I. scapularis in Canada. However, how important migratory birds from the United States are for the establishment and the stable endemic transmission cycle of Lyme disease in Canada remains an issue of theoretical challenge and practical significance. In this paper, we design and analyze a periodic model of differential equations with a forcing term modeling the annual bird migration to address the aforementioned issue. Our results show that ticks can establish in any migratory bird stopovers and breeding sites. Moreover, bird-transported ticks may increase the probability of B.burgdorferi establishment in a tick-endemic habitat.

Dengue Virus in Sub-tropical Northern and Central Viet Nam: Population Immunity and Climate Shape Patterns of Viral Invasion and Maintenance

Dengue virus transmission occurs in both epidemic and endemic cycles across tropical and sub-tropical regions of the world. Incidence is particularly high in much of Southeast Asia, where hyperendemic transmission plagues both urban and rural populations. However, endemicity has not been established in some areas with climates that may not support year-round viral transmission. An understanding of how dengue viruses (DENV) enter these environments and whether the viruses persist in inapparent local transmission cycles is central to understanding how dengue emerges in areas at the margins of endemic transmission. Dengue is highly endemic in tropical southern Vietnam, while increasingly large seasonal epidemics have occurred in northern Viet Nam over the last decade. We have investigated the spread of DENV-1 throughout Vietnam to determine the routes by which the virus enters northern and central regions of the country. Phylogeographic analysis of 1,765 envelope (E) gene sequences from Southeast Asia revealed frequent movement of DENV between neighboring human populations and strong local clustering of viral lineages. Long-distance migration of DENV between human population centers also occurred regularly and on short time-scales, indicating human-mediated viral invasion into northern Vietnam. Human populations in southern Vietnam were found to be the primary source of DENV circulating throughout the country, while central and northern Vietnam acted as sink populations, likely due to reduced connectedness to other populations in the case of the central regions and to the influence of temperature variability on DENV replication and vector survival and competence in the north. Finally, phylogeographic analyses suggested that viral movement follows a gravity model and indicates that population immunity and physical and economic connections between populations may play important roles in shaping patterns of DENV transmission.

Southernmost Asia Is the Source of Japanese Encephalitis Virus (Genotype 1) Diversity from which the Viruses Disperse and Evolve throughout Asia

BackgroundAlthough a previous study predicted that Japanese encephalitis virus (JEV) originated in the Malaysia/Indonesia region, the virus is known to circulate mainly on the Asian continent. However, there are no reported systematic studies that adequately define how JEV then dispersed throughout Asia.Methodology/Principal FindingsIn order to understand the mode of JEV dispersal throughout the entire Asian continent and the factors that determine the dispersal characteristics of JEV, a phylogenetic analysis using Bayesian Markov chain Monte Carlo simulations was conducted on all available JEV E gene sequences in GenBank, plus strains recently isolated in China. Here we demonstrate for the first time that JEV lineages can be divided into four endemic cycles, comprising southern Asia, eastern coastal Asia, western Asia, and central Asia. The isolation places of the viruses in each endemic cycle were geographically independent regardless of years, vectors, and hosts of isolation. Following further analysis, we propose that the southernmost region (Thailand, Vietnam, and Yunnan Province, China) was the source of JEV transmission to the Asian continent following its emergence. Three independent transmission routes from the south to north appear to define subsequent dispersal of JEV. Analysis of JEV population dynamics further supports these concepts.Conclusions/SignificanceThese results and their interpretation provide new insights into our understanding of JEV evolution and dispersal and highlight its potential for introduction into non-endemic areas.

Usutu Virus in Migratory Song Thrushes, Spain

Usutu Virus in Migratory Song Thrushes, Spain

The emergence of wildlife species as a source of human rabies infection in Brazil

Forty-five human rabies virus isolates from a wide geographical area of Brazil were characterized using an anti-nucleoprotein monoclonal antibody panel and by partial nucleotide sequencing analysis of the nucleoprotein gene. Three major antigenic groups related to the antigenic variants maintained in domestic dogs, vampire bats and marmosets were identified. Phylogenetic analyses revealed that the viruses from dog-related cases segregated into four sister clades: three associated with dog-endemic cycles in Brazil and one with the crab-eating fox cycle in the northeastern region of the country. The vampire bat- and marmoset-related viruses formed two independent groups. The topology of these clades was conserved when these samples were compared to virus representatives of the currently reported rabies endemic cycles in the Americas. These results indicated the presence of multiple endemic transmission cycles maintained in four different reservoirs, domestic dogs, crab-eating foxes, vampire bats and marmosets, which are being transmitted directly to humans and should be considered as a high-risk for rabies infection.

Babesia spp. and Anaplasma phagocytophilum in questing ticks, ticks parasitizing rodents and the parasitized rodents – Analyzing the host-pathogen-vector interface in a metropolitan area

BackgroundThe aims of this study were to evaluate the host-tick-pathogen interface of Babesia spp. and Anaplasma phagocytophilum in restored areas in both questing and host-attached Ixodes ricinus and Dermacentor reticulatus and their small mammalian hosts.MethodsQuesting ticks were collected from 5 sites within the city of Leipzig, Germany, in 2009. Small mammals were trapped at 3 of the 5 sites during 2010 and 2011. DNA extracts of questing and host-attached I. ricinus and D. reticulatus and of several tissue types of small mammals (the majority bank voles and yellow-necked mice), were investigated by PCR followed by sequencing for the occurrence of DNA of Babesia spp. and by real-time PCR for A. phagocytophilum. A selected number of samples positive for A. phagocytophilum were further investigated for variants of the partial 16S rRNA gene. Co-infection with Rickettsia spp. in the questing ticks was additionally investigated.Results4.1% of questing I. ricinus ticks, but no D. reticulatus, were positive for Babesia sp. and 8.7% of I. ricinus for A. phagocytophilum. Sequencing revealed B. microti, B. capreoli and Babesia spp. EU1 in Leipzig and sequence analysis of the partial 16S RNA gene of A. phagocytophilum revealed variants either rarely reported in human cases or associated with cervid hosts. The statistical analysis revealed significantly less ticks infected with A. phagocytophilum in a city park in Leipzig as compared to the other sampling sites. A. phagocytophilum-DNA was detected in 2 bank voles, DNA of B. microti in 1 striped field-mouse and of Babesia sp. EU1 in the skin tissue of a mole. Co-infections were detected.ConclusionOur results show the involvement of small mammals in the natural endemic cycles of tick-borne pathogens. A more thorough understanding of the interactions of ticks, pathogens and hosts is the essential basis for effective preventive control measures.

Towards a West Nile Virus Vaccine

Towards a West Nile Virus Vaccine West Nile virus (WNV) is a significant mosquito-borne human pathogen belonging to the Flaviviridae family with dengue, yellow fever, and Japanese encephalitis viruses. Recently, WNV has emerged as an important public health concern in the Western hemisphere, where it has established an endemic zoonotic cycle. Outcomes of WNV infection range from benign, non-symptomatic infection to flu-like febrile illness to severe central nervous system (CNS) manifestations.

Rabies in southeast Brazil: a change in the epidemiological pattern

This epidemiological study was conducted using antigenic and genetic characterisation of rabies virus isolates obtained from different animal species in the southeast of Brazil from 1993 to 2007. An alteration in the epidemiological profile was observed. One hundred two samples were tested using a panel of eight monoclonal antibodies, and 94 were genetically characterised by sequencing the nucleoprotein gene. From 1993 to 1997, antigenic variant 2 (AgV-2), related to a rabies virus maintained in dog populations, was responsible for rabies cases in dogs, cats, cattle and horses. Antigenic variant 3 (AgV-3), associated with Desmodus rotundus, was detected in a few cattle samples from rural areas. From 1998 to 2007, rabies virus was detected in bats and urban pets, and four distinct variants were identified. A nucleotide similarity analysis resulted in two primary groups comprising the dog and bat antigenic variants and showing the distinct endemic cycles maintained in the different animal species in this region.

Oocysts of Hepatozoon canis in Rhipicephalus ( Boophilus) microplus collected from a naturally infected dog

Canine hepatozoonosis is a tick-borne disease caused by protozoans of the genus Hepatozoon. Several tick species have been implicated as potential vectors. Therefore, extensive studies are needed to determine the ‘natural’ endemic cycle of this parasite. This paper presents the first report of the presence of Hepatozoon canis oocysts in Rhipicephalus ( Boophilus) microplus collected from an infected dog.

Diverse Borrelia burgdorferi strains in a bird-tick cryptic cycle.

The blacklegged tick Ixodes scapularis is the primary vector of the most prevalent vector-borne zoonosis in North America, Lyme disease (LD). Enzootic maintenance of the pathogen Borrelia burgdorferi by I. scapularis and small mammals is well documented, whereas its "cryptic" maintenance by other specialist ticks and wildlife hosts remains largely unexplored because these ticks rarely bite humans. We quantified B. burgdorferi infection in a cryptic bird-rabbit-tick cycle. Furthermore, we explored the role of birds in maintaining and moving B. burgdorferi strains by comparing their genetic diversity in this cryptic cycle to that found in cycles vectored by I. scapularis. We examined birds, rabbits, and small mammals for ticks and infection over a 4-year period at a focal site in Michigan, 90 km east of a zone of I. scapularis invasion. We mist netted 19,631 birds that yielded 12,301 ticks, of which 86% were I. dentatus, a bird-rabbit specialist. No resident wildlife harbored I. scapularis, and yet 3.5% of bird-derived ticks, 3.6% of rabbit-derived ticks, and 20% of rabbit ear biopsy specimens were infected with B. burgdorferi. We identified 25 closely related B. burgdorferi strains using an rRNA gene intergenic spacer marker, the majority (68%) of which had not been reported previously. The presence of strains common to both cryptic and endemic cycles strongly implies bird-mediated dispersal. Given continued large-scale expansion of I. scapularis populations, we predict that its invasion into zones of cryptic transmission will allow for bridging of novel pathogen strains to humans and animals.

Phylogeography of West Nile Virus: from the Cradle of Evolution in Africa to Eurasia, Australia, and the Americas

West Nile virus (WNV) is the most widely distributed of the encephalitic flaviviruses and is a major cause of encephalitis, with isolates obtained from all continents, apart from Antarctica. Subsequent to its divergence from the other members of the Japanese encephalitis virus complex, presumably in Africa, WNV has diverged into individual lineages that mostly correspond with geographic distribution. Here we elucidate the phylogeography and evolutionary history of isolates from lineage 1 of WNV. Interestingly, there are many examples of the same amino acid having evolved independently on multiple occasions. In Africa, WNV exists in an endemic cycle, whereas it is epidemic in Europe, being reintroduced regularly from Africa either directly (in western Europe) or via the Middle East (in eastern Europe). Significantly, introduction into other geographic areas has occurred on one occasion only in each region, leading to subsequent establishment and expansion of the virus in these areas. Only one endemic genotype each is present in India and Australia, suggesting that WNV was successfully introduced into these locations once only. Each introduction occurred many centuries ago, probably due to trade and exploration during the 19th century. Likewise, in the Americas, WNV was successfully introduced in 1999 and subsequently became endemic across most temperate regions of North America (NA). In contrast to previous suggestions, an isolate from the epidemic in Israel in 1998 was not the direct progenitor of the NA epidemic; rather, both epidemics originated from the same (unknown) location.

West Nile Virus–Neutralizing Antibodies in Humans in Greece

Serum samples collected during March-May 2007 from 392 residents of Imathia prefecture, Northern Greece, were tested by indirect immunofluorescence assay and enzyme-linked immunosorbent assay for IgG antibodies against West Nile virus (WNV). Microneutralization assay was applied in six positive samples. Four (4/392, 1.02%) were found positive for WNV-neutralizing antibodies. None of the positive individuals had a history of travel in endemic area or flavivirus vaccination, suggesting that WNV, or an antigenically related flavivirus, circulates in an endemic sylvatic cycle, at least locally, in rural areas in Greece. Human, animal, and vector surveillance systems have to be implemented to provide an early detection of WNV activity in Greece.

Evaluating the control of HPAIV H5N1 in Vietnam: virus transmission within infected flocks reported before and after vaccination

BackgroundCurrently, the highly pathogenic avian influenza virus (HPAIV) of the subtype H5N1 is believed to have reached an endemic cycle in Vietnam. We used routine surveillance data on HPAIV H5N1 poultry outbreaks in Vietnam to estimate and compare the within-flock reproductive number of infection (R0) for periods before (second epidemic wave, 2004-5; depopulation-based disease control) and during (fourth epidemic wave, beginning 2007; vaccination-based disease control) vaccination.ResultsOur results show that infected premises (IPs) in the initial (exponential) phases of outbreak periods have the highest R0 estimates. The IPs reported during the outbreak period when depopulation-based disease control was implemented had higher R0 estimates than IPs reported during the outbreak period when vaccination-based disease control was used. In the latter period, in some flocks of a defined size and species composition, within-flock transmission estimates were not significantly below the threshold for transmission (R0 < 1).ConclusionsOur results indicate that the current control policy based on depopulation plus vaccination has protected the majority of poultry flocks against infection. However, in some flocks the determinants associated with suboptimal protection need to be further investigated as these may explain the current pattern of infection in animal and human populations.

Epidemiology of West Nile in Europe and in the Mediterranean Basin~!2009-11-17~!2009-12-11~!2010-04-22~!

In the last 30 years several cases of West Nile (WN) virus infection were reported in horses and humans in Europe and in the Mediterranean Basin. Most of them were determined by strains of the Lineage 1 included in the European Mediterranean/Kenyan cluster. Strains of this cluster are characterised by a moderate pathogenicity for horses and humans and limited or no pathogenicity for birds. In recent years, however, WN cases determined by strains grouped in the Israeli/American cluster of Lineage 1 or in the lineage 2 have been reported in Hungary and Austria. The role of migrating birds in introducing new viruses to Europe has been often demonstrated. The migratory birds, which may be infected in their African wintering places, carry the virus northward to European sites during spring migrations. In the past, the virus introduction determined occasional cases of WN. In the recent years, new epidemiological scenarios are developing. In few occasions it has been evidenced the capability of WNV strains of overwintering by using local birds and mosquitoes. Species of Culex amongst mosquitoes and magpies (Pica pica), carrion crows (Corvus corone) and rock pigeons (Columba livia) amongst resident birds are the most probable species involved in this hypothetical WND endemic cycle.

Epidemiology of West Nile in Europe and in the Mediterranean Basin

In the last 30 years several cases of West Nile (WN) virus infection were reported in horses and humans in Europe and in the Mediterranean Basin. Most of them were determined by strains of the Lineage 1 included in the European Mediterranean/Kenyan cluster. Strains of this cluster are characterised by a moderate pathogenicity for horses and humans and limited or no pathogenicity for birds. In recent years, however, WN cases determined by strains grouped in the Israeli/American cluster of Lineage 1 or in the lineage 2 have been reported in Hungary and Austria. The role of migrating birds in introducing new viruses to Europe has been often demonstrated. The migratory birds, which may be infected in their African wintering places, carry the virus northward to European sites during spring migrations. In the past, the virus introduction determined occasional cases of WN. In the recent years, new epidemiological scenarios are developing. In few occasions it has been evidenced the capability of WNV strains of overwintering by using local birds and mosquitoes. Species of Culex amongst mosquitoes and magpies (Pica pica), carrion crows (Corvus corone) and rock pigeons (Columba livia) amongst resident birds are the most probable species involved in this hypothetical WND endemic cycle.

Food-borne trematode infections of humans in the United States of America

This review examines the literature on imported (allochthonous) and local (autochthonous) cases of food-borne trematode (FBT) infections in the United States of America (USA) from 1890 to 2009. Most of the literature is concerned with imported cases of the opisthorchiids Clonorchis sinensis and Opisthorchis viverrini. These flukes cause serious pathology in the liver and biliary system of humans. Chronic cases may induce liver (hepatocarcinoma) and bile duct (cholangiocarcinoma) cancers in humans. Clonorchiasis and opithorchiasis are preventable diseases that can be avoided by eating properly cooked freshwater fish products. Several species of lung flukes in the genus Paragonimus are local or imported FBT in the USA. The endemic cycle occurs in the USA with various local snails and crustaceans serving as intermediate hosts. Paragonimids are acquired when humans eat raw or improperly cooked freshwater crustaceans containing metacercarial cysts. Infection can cause severe lung disease and the symptoms of paragonimiasis often mimic those of tuberculosis and other non-helminthic diseases. Paragonimiasis can be avoided by not eating raw or improperly cooked shellfish. The liver fluke Fasciola hepatica can be acquired by eating raw or uncooked vegetation. The cycle exists in the USA involving local snails and aquatic vegetation. Although some cases are local, most are imported by travelers or immigrants. Fascioliasis can cause serious liver and biliary diseases in humans and consumption of tainted vegetation should be avoided. Lesser known FBT have been reported in the USA including species of Alaria, echinostomids, heterophyids, troglotrematids, and a self-induced infection of Plagiorchis. Treatment of the FBT mentioned in this review consists of various regimens of praziquantel, except for F. hepatica where the drug of choice is triclabendazole.

Booms and Busts: New Keynesian and Behavioral Explanations

Capitalism is characterized by booms and busts. Periods of strong growth in output alternate with periods of declines in economic growth. Every macro-economic theory should attempt to explain these endemic business cycle movements. In this paper I present two paradigms that attempt to explain these booms and busts. One is the DSGE-paradigm in which agents have unlimited cognitive abilities. The other paradigm is a behavioural one in which agents are assumed to have limited cognitive abilities. These two types of models produce a radically different macroeconomic dynamics. I analyze these differences. I also study the different policy implications of these two paradigms.