Gwenaël Vourc’h

Co-infection of Ticks: The Rule Rather Than the Exception

Introduction Ticks are the most common arthropod vectors of both human and animal diseases in Europe, and the Ixodes ricinus tick species is able to transmit a large number of bacteria, viruses and parasites. Ticks may also be co-infected with several pathogens, with a subsequent high likelihood of co-transmission to humans or animals. However few data exist regarding co-infection prevalences, and these studies only focus on certain well-known pathogens. In addition to pathogens, ticks also carry symbionts that may play important roles in tick biology, and could interfere with pathogen maintenance and transmission. In this study we evaluated the prevalence of 38 pathogens and four symbionts and their co-infection levels as well as possible interactions between pathogens, or between pathogens and symbionts. Methodology/principal findings A total of 267 Ixodes ricinus female specimens were collected in the French Ardennes and analyzed by high-throughput real-time PCR for the presence of 37 pathogens (bacteria and parasites), by rRT-PCR to detect the presence of Tick-Borne encephalitis virus (TBEV) and by nested PCR to detect four symbionts. Possible multipartite interactions between pathogens, or between pathogens and symbionts were statistically evaluated. Among the infected ticks, 45% were co-infected, and carried up to five different pathogens. When adding symbiont prevalences, all ticks were infected by at least one microorganism, and up to eight microorganisms were identified in the same tick. When considering possible interactions between pathogens, the results suggested a strong association between Borrelia garinii and B. afzelii, whereas there were no significant interactions between symbionts and pathogens. Conclusion/significance Our study reveals high pathogen co-infection rates in ticks, raising questions about possible co-transmission of these agents to humans or animals, and their consequences to human and animal health. We also demonstrated high prevalence rates of symbionts co-existing with pathogens, opening new avenues of enquiry regarding their effects on pathogen transmission and vector competence.

The relationships between Ixodes ricinus and small mammal species at the woodland–pasture interface

Ixodes ricinus, as vector, and small mammals, as reservoirs, are implicated in pathogen transmission between wild fauna, domestic animals and humans at the woodland–pasture interface. The ecological relationship between ticks and small mammals was monitored in 2005 on four bocage (enclosed pastureland) sites in central France, where questing ticks were collected by dragging and small mammals were trapped. Questing I. ricinus tick and small mammal locations in the environment were assessed through correspondence analysis. I. ricinus larval burden on small mammals was modeled using a negative binomial law. The correspondence analyses underlined three landscape features: grassland, hedgerow, and woodland. Seven small mammal species were trapped, while questing ticks were all I. ricinus, with the highest abundance in woodland and the lowest in pasture. The small mammals were overall more abundant in hedgerow, less present in woodland and sparse in grassland. They carried mainly I. ricinus, and secondarily I. acuminatus and I. trianguliceps. The most likely profile for a tick-infested small mammal corresponded to a male wood mouse (Apodemus sylvaticus) in woodland or hedgerow during a dry day. A. sylvaticus, which was the only species captured in grassland, but was also present in hedgerow and woodland, may be a primary means of transfer of I. ricinus larvae from woodland to pasture.

Introduced Siberian chipmunks (Tamias sibiricus barberi) contribute more to lyme borreliosis risk than native reservoir rodents.

The variation of the composition in species of host communities can modify the risk of disease transmission. In particular, the introduction of a new host species can increase health threats by adding a new reservoir and/or by amplifying the circulation of either exotic or native pathogens. Lyme borreliosis is a multi-host vector-borne disease caused by bacteria belonging to the Borrelia burgdorferi sensu lato complex. It is transmitted by the bite of hard ticks, especially Ixodes ricinus in Europe. Previous studies showed that the Siberian chipmunk, Tamias sibiricus barberi, an introduced ground squirrel in the Forest of Sénart (near Paris, France) was highly infested by I. ricinus, and consequently infected by B. burgdorferi sl. An index of the contribution of chipmunks to the density of infected questing nymphs on the vegetation (i.e., the acarological risk for humans) was compared to that of bank voles (Myodes glareolus) and of wood mice (Apodemus sylvaticus), two known native and sympatric competent reservoir hosts. Chipmunks produced nearly 8.5 times more infected questing nymphs than voles and mice. Furthermore, they contribute to a higher diversity of B. burgdorferi sl genospecies (B. afzelii, B. burgdorferi sensu stricto and B. garinii). The contribution of chipmunks varied between years and seasons, according to tick availability. As T. s. barberi must be a competent reservoir, it should amplify B. burgdorferi sl infection, hence increasing the risk of Lyme borreliosis in humans.

The importance of multiparasitism: examining the consequences of co-infections for human and animal health

Most parasites co-occur with other parasites, although the importance of such multiparasitism has only recently been recognised. Co-infections may result when hosts are independently infected by different parasites at the same time or when interactions among parasite species facilitate co-occurrence. Such interactions can have important repercussions on human or animal health because they can alter host susceptibility, infection duration, transmission risks, and clinical symptoms. These interactions may be synergistic or antagonistic and thus produce diverse effects in infected humans and animals. Interactions among parasites strongly influence parasite dynamics and therefore play a major role in structuring parasite populations (both within and among hosts) as well as host populations. However, several methodological challenges remain when it comes to detecting parasite interactions. The goal of this review is to summarise current knowledge on the causes and consequences of multiparasitism and to discuss the different methods and tools that researchers have developed to study the factors that lead to multiparasitism. It also identifies new research directions to pursue.

A new multiple-locus variable-number tandem repeat analysis reveals different clusters for Anaplasma phagocytophilum circulating in domestic and wild ruminants

BackgroundAnaplasma phagocytophilum is a tick-borne intragranulocytic alpha-proteobacterium. It is the causative agent of tick-borne fever in ruminants, and of human granulocytic anaplasmosis in humans, two diseases which are becoming increasingly recognized in Europe and the USA. However, while several molecular typing tools have been developed over the last years, few of them are appropriate for in-depth exploration of the epidemiological cycle of this bacterium. Therefore we have developed a Multiple-Locus Variable number tandem repeat (VNTR) Analysis typing technique for A. phagocytophilum.MethodsFive VNTRs were selected based on the HZ human-derived strain genome, and were tested on the Webster human-derived strain and on 123 DNA samples: 67 from cattle, 7 from sheep, 15 from roe deer, 4 from red deer, 1 from a reindeer, 2 from horses, 1 from a dog, and 26 from ticks.ResultsFrom these samples, we obtained 84 different profiles, with a diversity index of 0.96 (0.99 for vertebrate samples, i.e. without tick samples). Our technique confirmed that A. phagocytophilum from roe deer or domestic ruminants belong to two different clusters, while A. phagocytophilum from red deer and domestic ruminants locate within the same cluster, questioning the respective roles of roe vs red deer as reservoir hosts for domestic ruminant strains in Europe. As expected, greater diversity was obtained between rather than within cattle herds.ConclusionsOur technique has great potential to provide detailed information on A. phagocytophilum isolates, improving both epidemiological and phylogenic investigations, thereby helping in the development of relevant prevention and control measures.

Questionnaire-based survey on distribution and clinical incidence of canine babesiosis in France

BackgroundThe causative agent of canine babesiosis is the protozoan Babesia canis, transmitted by the tick Dermacentor reticulatus within France. While the parasite can be found everywhere in France however cases of infection are associated with distinct geographical foci. The aim of the study was to evaluate the clinical occurrence of canine babesiosis diagnosed in veterinary clinics in order to propose an updated map of the disease distribution in France.ResultsQuestionnaires were sent via email to all canine veterinary clinics in continental France. Information collected included the number of babesiosis cases diagnosed in 2010, the number of veterinary practitioners and the location of the clinic. The total number of dogs and practitioners per administrative department were used to define the reference population. The annual incidence rate of canine babesiosis per department was calculated as the ratio between the number of babesiosis cases reported by the clinics and the total number of dogs in the clinics of the same department. Data were geo-referenced for map construction (Quantum GIS version 1.7.4). The overall annual incidence rate of clinical babesiosis among the surveyed population was 1.07% (CI95 1.05-1.09) with geographical variations between departments, ranging from 0.01% to 16.05%. Four enzootic areas were identified: South-West, Center, East and Paris area. The South-West region should be considered as a hyper-enzootic area with the higher incidence rates.ConclusionOur results confirmed the burden of canine babesiosis in France. In the context of tick-borne disease emergence in Europe, the risk for canine babesiosis may become more significant in other European countries in the coming years.

Chikungunya antibodies detected in non-human primates and rats in three Indian Ocean islands after the 2006 ChikV outbreak.

The role of terrestrial vertebrates in the epidemiology of chikungunya disease is poorly understood. We evaluated their exposure and amplification role during the 2006 chikungunya outbreak in the Indian Ocean. Blood samples were collected from 18 mammalian and reptile species from Reunion Island, Mauritius and Mayotte. Among the 1051 samples serologically tested for chikungunya virus (CHIKV), two crab-eating macaques (Macaca fascicularis) and two ship rats (Rattus rattus) proved to be exposed to CHIKV. CHIKV RNA was not detected in 791 analyzed sera. Our results confirm the preferential infection of simian primates and suggest that other vertebrates played a poor or no role in CHIKV transmission during the 2006 outbreak.

Multilocus sequence analysis of Anaplasma phagocytophilum reveals three distinct lineages with different host ranges in clinically ill French cattle

Molecular epidemiology represents a powerful approach to elucidate the complex epidemiological cycles of multi-host pathogens, such as Anaplasma phagocytophilum. A. phagocytophilum is a tick-borne bacterium that affects a wide range of wild and domesticated animals. Here, we characterized its genetic diversity in populations of French cattle; we then compared the observed genotypes with those found in horses, dogs, and roe deer to determine whether genotypes of A. phagocytophilum are shared among different hosts. We sampled 120 domesticated animals (104 cattle, 13 horses, and 3 dogs) and 40 wild animals (roe deer) and used multilocus sequence analysis on nine loci (ankA, msp4, groESL, typA, pled, gyrA, recG, polA, and an intergenic region) to characterize the genotypes of A. phagocytophilum present. Phylogenic analysis revealed three genetic clusters of bacterial variants in domesticated animals. The two principal clusters included 98% of the bacterial genotypes found in cattle, which were only distantly related to those in roe deer. One cluster comprised only cattle genotypes, while the second contained genotypes from cattle, horses, and dogs. The third contained all roe deer genotypes and three cattle genotypes. Geographical factors could not explain this clustering pattern. These results suggest that roe deer do not contribute to the spread of A. phagocytophilum in cattle in France. Further studies should explore if these different clusters are associated with differing disease severity in domesticated hosts. Additionally, it remains to be seen if the three clusters of A. phagocytophilum genotypes in cattle correspond to distinct epidemiological cycles, potentially involving different reservoir hosts.

How Does Biodiversity Influence the Ecology of Infectious Disease

Over the past years, biodiversity has been reduced on an unprecedented scale, while new infectious diseases are emerging at an increasing rate. Greater overall biodiversity could lead to a greater diversity of hosts and thus of pathogens. Yet disease regulation – due to the buffering role of host diversity – is considered to be one of the services provided by biodiversity. In this chapter, we ask how biodiversity is linked to infectious disease. First, we investigate the influence of the biodiversity of pathogens. We highlight that the number of pathogen species is not well known but that new findings are facilitated by the rapid expansion of molecular techniques. We show that, although there is a trend to find higher pathogen richness toward the equator, identifying a global pattern between the richness of all pathogen species and their latitudinal distribution is challenging. We emphasize that pathogen intraspecific diversity is a crucial factor in disease emergence and allows pathogens to adapt to the selective pressures they face. In addition, the selective pressure acting on hosts due to parasite, and reinforced by parasite diversity within hosts seems to be a major evolutionary and ecological force shaping hosts biodiversity. Second, we investigate how the diversity of hosts influences infectious disease ecology. For multi-host diseases, a change in host species richness or abundance can modify the dynamics of local infectious diseases by either reducing (“dilution effect”) or increasing (“amplification effect”) the risk of transmission to the targeted host species. The underlying hypothesis is that, the competence of reservoirs varies according to the host species. The dilution effect has been demonstrated mainly through theoretical work and there have been only few case studies. Regarding the genetic diversity of host, an important issue is: to what extent does a reduction of this diversity impact the ability of the host population to response to infectious diseases? Third, we rapidly examine the role of biodiversity in the treatment of infectious diseases. To conclude, we consider that the consequences of the loss of species biodiversity on infectious diseases is still largely unknown, notably due to the lack of knowledge on the dynamics of host-pathogen relationships, especially at the population and at the community level.. We highlight that work on multi-host/ ulti-pathogen systems should be fostered and that new approaches, such as metagenomic investigations that does not require a priori assumptions, are promising to describe a community of pathogens and their interactions.

Strong evidence for the presence of the tick Hyalomma marginatum Koch, 1844 in southern continental France.

Hyalomma ticks can transmit several human and animal pathogens in Eurasia and Africa. Interest in Hyalomma marginatum has increased since the recent (re)emergence of Crimean-Congo Hemorrhagic fever in the Palearctic region. Until now, continental France has been considered free of this tick species. Nevertheless, the existence of incomplete and occasionally incorrect records has maintained confusion about its status. Based on several tick sampling campaigns conducted on horses and birds from 2007 to 2016, we provided very strong evidence for the presence of reproducing populations of H. marginatum in parts of southern continental France. We also confirmed the introduction of immature developmental stages of H. marginatum, as well as H. rufipes, into France probably through trans-Mediterranean bird migrations.