Using environmental DNA for detection of Batrachochytrium salamandrivorans in natural water

Rapid, early, and reliable detection of invasive pathogenic microorganisms is essential in order to either predict or delineate an outbreak, and monitor appropriate mitigation measures. The chytrid fungus Batrachochytrium salamandrivorans is expanding in Europe, and infection with this fungus may cause massive mortality in urodelans (salamanders and newts). In this study, we designed and validated species‐specific primers and a probe for detection of B. salamandrivorans in water. In a garden pond in close proximity to the B. salamandrivorans index site in the Netherlands, B. salamandrivorans‐infected newts had been detected in 2015 and have been monitored since. In 2016 and 2017, no B. salamandrivorans was detected at this site, but in 2018 B. salamandrivorans flared up in this isolated pond which allowed validation of the technique in situ. We here present the development of an environmental DNA technique that successfully detects B. salamandrivorans DNA in natural waterbodies even at low concentrations. This technique may be further validated to play a role in B. salamandrivorans range delineation and surveillance in both natural waterbodies and in captive collections

Keeping track of the enemy : Flight analyses of the host-seeking malaria mosquito Anopheles gambiae s.s

Female mosquitoes can transmit pathogens to their host during blood feeding and are an important vector of human diseases such as dengue, chikungunya, filariasis and malaria. After 15 years of decline in the number of fatal malaria cases, this decline came to a halt in 2016. Growing resistance against drugs and insecticides pose a serious threat for future human health. This thesis focuses on the behaviour of host-seeking malaria mosquitoes by analysing their flight paths during their approach to different host cues. Fundamental knowledge on the role of selected host cues was acquired. In addition, studies to support successful implementation of vector control interventions were performed in both wind-tunnel settings and the semi-field in Kenya. My research demonstrates that automated tracking systems can strengthen behavioural-ecological studies on disease vectors, in addition to conventional bio-assays such as olfactometers, by providing detailed information on the approach behaviour of mosquitoes to different targets. The attraction towards the host-sensory cue CO2 was investigated in an olfactometer bioassay. Trap catches of female Anopheles gambiae s.s. were enhanced by separation of the CO2 source from the source of human skin emanations. Close-range deterrent effects of CO2 were overcome by the simultaneous presence of skin emanations. Flight path analysis of mosquitoes in a wind tunnel, showed that exposure to human odour resulted in prolonged and highly convoluted flight tracks. The combination of odour with heat was crucial to induce landings of host-seeking mosquitoes. A semi-field study in Kenya revealed that house-entering mosquitoes approached the eave of a house in a wide angle to the house at eave level, where the proportion that entered uninterruptedly (23%) spent just a few seconds around the eave area. The presence of insecticide-treated nets inside a house did not repel mosquitoes as measured by the number of house entries. At close range, in a wind tunnel, free-flight exposure of mosquitoes to deltamethrin-treated nets in combination with human odour did not reveal any (excito-) repellent effect and resulted in lower mortality rates compared to standard bioassays where contact with the treated material is enforced. The knowledge obtained on the behavioural responses of mosquitoes to host cues has indirectly affected vector control tool implementations in the field. For example, in the development of an odour-baited trap, a CO2 release pipe was included that is separated from the attractive odour plume. The role of heat was exploited in the development of a repellent bioassay and a heat source was added to another trap model. Insights in house-entry behaviour and mosquito responses to bed nets support the successful implementation of push-pull systems, installation of eave tubes or implementing house improvement operations to reduce malaria transmission. An integrated vector management approach is required to further develop existing control tools by adding and improving alternative intervention techniques.</p

Investigation of amphibian mortality events in wildlife reveals an on-going ranavirus epidemic in the North of the Netherlands

In the four years following the first detection of ranavirus (genus Ranavirus, family Iridoviridae) infection in Dutch wildlife in 2010, amphibian mortality events were investigated nationwide to detect, characterize and map ranaviruses in amphibians over time, and to establish the affected host species and the clinico-pathological presentation of the disease in these hosts. The ultimate goal was to obtain more insight into ranavirus disease emergence and ecological risk. In total 155 dead amphibians from 52 sites were submitted between 2011 and 2014, and examined using histopathology, immunohistochemistry, virus isolation and molecular genetic characterization. Ranavirus-associated amphibian mortality events occurred at 18 sites (35%), initially only in proximity of the 2010 index site. Specimens belonging to approximately half of the native amphibian species were infected, including the threatened Pelobates fuscus (spadefoot toad). Clustered massive outbreaks involving dead adult specimens and ranavirus genomic identity indicated that one common midwife toad virus (CMTV)-like ranavirus strain is emerging in provinces in the north of the Netherlands. Modelling based on the spatiotemporal pattern of spread showed a high probability that this emerging virus will continue to be detected at new sites (the discrete reproductive power of this outbreak is 0.35). Phylogenetically distinct CMTV-like ranaviruses were found in the south of the Netherlands more recently. In addition to showing that CMTV-like ranaviruses threaten wild amphibian populations not only in Spain but also in the Netherlands, the current spread and risk of establishment reiterate that understanding the underlying causes of CMTV-like ranavirus emergence requires international attention

Use of habitat odour by host-seeking insects

Locating suitable feeding or oviposition sites is essential for insect survival. Understanding how insects achieve this is crucial, not only for understanding the ecology and evolution of insect–host interactions, but also for the development of sustainable pest-control strategies that exploit insects' host-seeking behaviours. Volatile chemical cues are used by foraging insects to locate and recognise potential hosts but in nature these resources usually are patchily distributed, making chance encounters with host odour plumes rare over distances greater than tens of metres. The majority of studies on insect host-seeking have focussed on short-range orientation to easily detectable cues and it is only recently that we have begun to understand how insects overcome this challenge. Recent advances show that insects from a wide range of feeding guilds make use of ‘habitat cues’, volatile chemical cues released over a relatively large area that indicate a locale where more specific host cues are most likely to be found. Habitat cues differ from host cues in that they tend to be released in larger quantities, are more easily detectable over longer distances, and may lack specificity, yet provide an effective way for insects to maximise their chances of subsequently encountering specific host cues. This review brings together recent advances in this area, discussing key examples and similarities in strategies used by haematophagous insects, soil-dwelling insects and insects that forage around plants. We also propose and provide evidence for a new theory that general and non-host plant volatiles can be used by foraging herbivores to locate patches of vegetation at a distance in the absence of more specific host cues, explaining some of the many discrepancies between laboratory and field trials that attempt to make use of plant-derived repellents for controlling insect pests

Using decision analysis to support proactive management of emerging infectious wildlife diseases

Despite calls for improved responses to emerging infectious diseases in wildlife, management is seldom considered until a disease has been detected in affected populations. Reactive approaches may limit the potential for control and increase total response costs. An alternative, proactive management framework can identify immediate actions that reduce future impacts even before a disease is detected, and plan subsequent actions that are conditional on disease emergence. We identify four main obstacles to developing proactive management strategies for the newly discovered salamander pathogen Batrachochytrium salamandrivorans (Bsal). Given that uncertainty is a hallmark of wildlife disease management and that associated decisions are often complicated by multiple competing objectives, we advocate using decision analysis to create and evaluate trade-offs between proactive (pre-emergence) and reactive (post-emergence) management options. Policy makers and natural resource agency personnel can apply principles from decision analysis to improve strategies for countering emerging infectious diseases

Seeing is believing: the nocturnal malarial mosquito Anopheles coluzzii responds to visual host-cues when odour indicates a host is nearby

Background: The immediate aim of our study was to analyse the behaviour of the malarial mosquito Anopheles coluzzii (An. gambiae species complex) near a human host with the ultimate aim of contributing to our fundamental understanding of mosquito host-seeking behaviour and the overall aim of identifying behaviours that could be exploited to enhance sampling and control strategies. Results: Based on 3D video recordings of individual host-seeking females in a laboratory wind-tunnel, we found that despite being a nocturnal species, An. coluzzii is highly responsive to a visually conspicuous object, but only in the presence of host-odour. Female mosquitoes approached and abruptly veered away from a dark object, which suggests attraction to visual cues plays a role in bringing mosquitoes to the source of host odour. It is worth noting that the majority of our recorded flight tracks consisted of highly stereotyped ‘dipping’ sequences near the ground, which have been mentioned in the literature, but never before quantified. Conclusions: Our quantitative analysis of female mosquito flight patterns within ~1.5 m of a host has revealed highly relevant information about responsiveness to visual objects and flight height that could revolutionise the efficacy of sampling traps; the capturing device of a trap should be visually conspicuous and positioned near the ground where the density of host-seeking mosquitoes would be greatest. These characteristics are not universally present in current traps for malarial mosquitoes. The characterisation of a new type of flight pattern that is prevalent in mosquitoes suggests that there is still much that is not fully understood about mosquito flight behaviour

Exploiting Anopheles responses to thermal, odour and visual stimuli to improve surveillance and control of malaria

Mosquito surveillance and control are at the heart of efforts to eliminate malaria, however, there remain significant gaps in our understanding of mosquito behaviour that impede innovation. We hypothesised that a combination of human-associated stimuli could be used to attract and kill malaria vectors more successfully than individual stimuli, and at least as well as a real human. To test this in the field, we quantified Anopheles responses to olfactory, visual and thermal stimuli in Burkina Faso using a simple adhesive trap. Traps baited with human odour plus high contrast visual stimuli caught more Anopheles than traps with odour alone, showing that despite their nocturnal habit, malaria vectors make use of visual cues in host-seeking. The best performing traps, however, combined odour and visual stimuli with a thermal signature in the range equivalent to human body temperature. When tested against a human landing catch during peak mosquito abundance, this “host decoy” trap caught nearly ten times the number of Anopheles mosquitoes caught by a human collector. Exploiting the behavioural responses of mosquitoes to the entire suite of host stimuli promises to revolutionise vector surveillance and provide new paradigms in disease control

Role of sand lizards in the ecology of Lyme and other tick-borne diseases in the Netherlands

<p>Abstract</p> <p>Background</p> <p>Lizards are considered zooprophylactic for almost all <it>Borrelia burgdorferi </it>species, and act as dilution hosts in parts of North America. Whether European lizards significantly reduce the ability of <it>B. burgdorferi </it>to maintain itself in enzootic cycles, and consequently decrease the infection rate of <it>Ixodes ricinus ticks </it>for <it>B. burgdorferi </it>and other tick-borne pathogens in Western Europe is not clear.</p> <p>Results</p> <p>Ticks were collected from sand lizards, their habitat (heath) and from the adjacent forest. DNA of tick-borne pathogens was detected by PCR followed by reverse line blotting. Tick densities were measured at all four locations by blanket dragging. Nymphs and adult ticks collected from lizards had a significantly lower (1.4%) prevalence of <it>B. burgdorferi </it>sensu lato, compared to questing ticks in heath (24%) or forest (19%). The prevalence of <it>Rickettsia helvetica </it>was significantly higher in ticks from lizards (19%) than those from woodland (10%) whereas neither was significantly different from the prevalence in ticks from heather (15%). The prevalence of <it>Anaplasma </it>and <it>Ehrlichia </it>spp in heather (12%) and forest (14%) were comparable, but significantly lower in ticks from sand lizards (5.4%). The prevalence of <it>Babesia </it>spp in ticks varied between 0 and 5.3%. Tick load of lizards ranged from 1 - 16. Tick densities were ~ 5-fold lower in the heather areas than in woodlands at all four sites.</p> <p>Conclusions</p> <p>Despite their apparent low reservoir competence, the presence of sand lizards had insignificant impact on the <it>B. burgdorferi </it>s.l. infection rate of questing ticks. In contrast, sand lizards might act as reservoir hosts for <it>R. helvetica</it>. Remarkably, the public health risk from tick-borne diseases is approximately five times lower in heather than in woodland, due to the low tick densities in heather.</p

Protein Tyrosine Phosphatase-Induced Hyperactivity Is a Conserved Strategy of a Subset of BaculoViruses to Manipulate Lepidopteran Host Behavior

This is the final version. Available from PLoS via the DOI in this record.Many parasites manipulate host behavior to increase the probability of transmission. To date, direct evidence for parasitic genes underlying such behavioral manipulations is scarce. Here we show that the baculovirus Autographa californica nuclear polyhedrovirus (AcMNPV) induces hyperactive behavior in Spodoptera exigua larvae at three days after infection. Furthermore, we identify the viral protein tyrosine phosphatase (ptp) gene as a key player in the induction of hyperactivity in larvae, and show that mutating the catalytic site of the encoded phosphatase enzyme prevents this induced behavior. Phylogenetic inference points at a lepidopteran origin of the ptp gene and shows that this gene is well-conserved in a group of related baculoviruses. Our study suggests that ptp-induced behavioral manipulation is an evolutionarily conserved strategy of this group of baculoviruses to enhance virus transmission, and represents an example of the extended phenotype concept. Overall, these data provide a firm base for a deeper understanding of the mechanisms behind baculovirus-induced insect behavior. © 2012 van Houte et al.Program Strategic Alliances of the Royal Dutch Academy of SciencesMEERVOUD grant from the Netherlands Organization for Scientific ResearchC.T. de Wit Graduate School for Production Ecology and Resource Conservatio