Climate Change and Highland Malaria: Fresh Air for a Hot Debate

In recent decades, malaria has become established in zones at the margin of its previous distribution, especially in the highlands of East Africa. Studies in this region have sparked a heated debate over the importance of climate change in the territorial expansion of malaria, where positions range from its neglect to the reification of correlations as causes. Here, we review studies supporting and rebutting the role of climatic change as a driving force for highland invasion by malaria. We assessed the conclusions from both sides of the argument and found that evidence for the role of climate in these dynamics is robust. However, we also argue that over-emphasizing the importance of climate is misleading for setting a research agenda, even one which attempts to understand climate change impacts on emerging malaria patterns. We review alternative drivers for the emergence of this disease and highlight the problems still calling for research if the multidimensional nature of malaria is to be adequately tackled. We also contextualize highland malaria as an ongoing evolutionary process. Finally, we present Schmalhausen's law, which explains the lack of resilience in stressed systems, as a biological principle that unifies the importance of climatic and other environmental factors in driving malaria patterns across different spatio-temporal scales

The role of volatiles in aggregation and host-seeking of the haematophagous poultry red mite Dermanyssus gallinae (Acari: Dermanyssidae)

Infestations with ectoparasitic poultry red mites (Dermanyssus gallinae) pose an increasing threat to poultry health and welfare. Because of resistance to acaricides and higher scrutiny of poultry products, alternative and environmentally safe management strategies are warranted. Therefore, we investigated how volatile cues shape the behavior of D. gallinae and how this knowledge may be exploited in the development of an attractand- kill method to control mite populations. A Y-tube olfactometer bio-assay was used to evaluate choices of mites in response to cues related to conspecific mites as well as related to their chicken host. Both recently fed and starved mites showed a strong preference (84 and 85%, respectively) for volatiles from conspecific, fed mites as compared to a control stream of clean air. Mites were also significantly attracted to ‘aged feathers’ (that had remained in the litter for 3–4 days), but not to ‘fresh feathers’. Interestingly, an air stream containing 2.5% CO2, which mimics the natural concentration in air exhaled by chickens, did attract fed mites, but inhibited the attraction of unfed mites towards volatiles from aged feathers. We conclude that both mite-related cues (aggregation pheromones) and host-related cues (kairomones) mediate the behavior of the poultry mite. We discuss the options to exploit this knowledge as the ‘attract’ component of attract-and-kill strategies for the control of D. gallina

Evaluation of Methods for Sampling the Malaria Vector Anopheles darlingi (Diptera, Culicidae) in Suriname and the Relation With Its Biting Behavior

The effectiveness of CO2-baited and human-baited mosquito traps for the sampling of Anopheles darlingi Root was evaluated and compared with human landing collections in Suriname. Biting preferences of this mosquito on a human host were studied and related to trapping data. Traps used were the Centers for Disease Control and Prevention Miniature Light trap, the BG Sentinel mosquito trap, the Mosquito Magnet Liberty Plus mosquito trap (MM-Plus), and a custom-designed trap. Carbon dioxide and humans protected by a bed net were used as bait in the studies. The number of An. darlingi collected was greater with human landing collections than with all other collection methods. An. darlingi did not show a preference for protected humans over CO2 bait. The BG Sentinel mosquito trap with CO2 or human odor as bait and the MM-Plus proved the best alternative sampling tools for An. darlingi. The BG Sentinel mosquito trap with CO2 or human odor as bait was also very efficient at collecting Culex spp. In a field study on biting preferences of wild An. darlingi, the females showed directional biting behavior (P <0.001), with a majority of females (93.3%) biting the lower legs and feet when approaching a seated human host. Higher efficiency of the closer-to-the-ground collecting MM-Plus and BG Sentinel mosquito trap when compared with the other trapping methods may be a result of a possible preference of this mosquito species for low-level biting. It is concluded that odor-baited sampling systems can reliably collect An. darlingi, but the odor bait needs to be improved, for instance, by including host-specific volatiles, to match live human baits

Carbon dioxide baited trap catches do not correlate with human landing collections of Anopheles aquasalis in Suriname

Three types of carbon dioxide-baited traps, i.e., the Centers for Disease Control Miniature Light Trap without light, the BioGents (BG) Sentinel Mosquito Trap (BG-Sentinel) and the Mosquito Magnet® Liberty Plus were compared with human landing collections in their efficiency in collecting Anopheles (Nyssorhynchus) aquasalis mosquitoes. Of 13,549 total mosquitoes collected, 1,019 (7.52%) were An. aquasalis. Large numbers of Culex spp were also collected, in particular with the (BG-Sentinel). The majority of An. aquasalis (83.8%) were collected by the human landing collection (HLC). None of the trap catches correlated with HLC in the number of An. aquasalis captured over time. The high efficiency of the HLC method indicates that this malaria vector was anthropophilic at this site, especially as carbon dioxide was insufficiently attractive as stand-alone bait. Traps using carbon dioxide in combination with human odorants may provide better results

The invasive Asian bush mosquito Aedes japonicus found in the Netherlands can experimentally transmit Zika virus and Usutu virus

Background - The Asian bush mosquito Aedes japonicus is invading Europe and was first discovered in Lelystad, the Netherlands in 2013, where it has established a permanent population. In this study, we investigated the vector competence of Ae. japonicus from the Netherlands for the emerging Zika virus (ZIKV) and zoonotic Usutu virus (USUV). ZIKV causes severe congenital microcephaly and Guillain-Barré syndrome in humans. USUV is closely related to West Nile virus, has recently spread throughout Europe and is causing mass mortality of birds. USUV infection in humans can result in clinical manifestations ranging from mild disease to severe neurological impairments.Methodology/Principal findings - In our study, field-collected Ae. japonicus females received an infectious blood meal with ZIKV or USUV by droplet feeding. After 14 days at 28°C, 3% of the ZIKV-blood fed mosquitoes and 13% of the USUV-blood fed mosquitoes showed virus-positive saliva, indicating that Ae. japonicus can transmit both viruses. To investigate the effect of the mosquito midgut barrier on virus transmission, female mosquitoes were intrathoracically injected with ZIKV or USUV. Of the injected mosquitoes, 96% (ZIKV) and 88% (USUV) showed virus-positive saliva after 14 days at 28°C. This indicates that ZIKV and USUV can efficiently replicate in Ae. japonicus but that a strong midgut barrier is normally restricting virus dissemination. Small RNA deep sequencing of orally infected mosquitoes confirmed active replication of ZIKV and USUV, as demonstrated by potent small interfering RNA responses against both viruses. Additionally, de novo small RNA assembly revealed the presence of a novel narnavirus in Ae. japonicus.Conclusions/Significance - Given that Ae. japonicus can experimentally transmit arthropod-borne viruses (arboviruses) like ZIKV and USUV and is currently expanding its territories, we should consider this mosquito as a potential vector for arboviral diseases in Europ

Community mobilization for malaria elimination: application of an open space methodology in Ruhuha sector, Rwanda

Background Despite the significant reduction of malaria transmission in Rwanda, Ruhuha sector is still a highly endemic area for malaria. The objective of this activity was to explore and brainstorm the potential roles of various community stakeholders in malaria elimination. Methods Horizontal participatory approaches such as ‘open space’ have been deployed to explore local priorities, stimulate community contribution to project planning, and to promote local capacity to manage programmes. Two open space meetings were conducted with 62 and 82 participants in years 1 and 2, respectively. Participants included purposively selected community and local organizations’ representatives. Results Malaria was perceived as a health concern by the respondents despite the reported reduction in prevalence from 60 to 20% for cases at the local health centre. Some misconceptions of the cause of malaria and misuse of preventive strategies were noted. Poverty was deemed to be a contributing factor to malaria transmission, with suggestions that improvement of living conditions for poor families might help malaria reduction. Participants expressed willingness to contribute to malaria elimination and underscored the need for constant education, sensitization and mobilization towards malaria control in general. Active diagnosis, preventative strategies and prompt treatment of malaria cases were all mentioned by participants as ways to reduce malaria. Participants suggested that partnership of stakeholders at various levels could speed up programme activities. A community rewards system was deemed important to motivate engaged participants, i.e., community health workers and households. Establishment of malaria clubs in schools settings was also suggested as crucial to speed up community awareness and increase skills towards further malaria reduction. Conclusions This bottom-up approach was found useful in engaging the local community, enabling them to explore issues related to malaria in the area and suggest solutions for sustainable malaria elimination gains

Fine Scale Spatiotemporal Clustering of Dengue Virus Transmission in Children and Aedes aegypti in Rural Thai Villages

Background Based on spatiotemporal clustering of human dengue virus (DENV) infections, transmission is thought to occur at fine spatiotemporal scales by horizontal transfer of virus between humans and mosquito vectors. To define the dimensions of local transmission and quantify the factors that support it, we examined relationships between infected humans and Aedes aegypti in Thai villages. Methodology/Principal Findings Geographic cluster investigations of 100-meter radius were conducted around DENV-positive and DENV-negative febrile “index” cases (positive and negative clusters, respectively) from a longitudinal cohort study in rural Thailand. Child contacts and Ae. aegypti from cluster houses were assessed for DENV infection. Spatiotemporal, demographic, and entomological parameters were evaluated. In positive clusters, the DENV infection rate among child contacts was 35.3% in index houses, 29.9% in houses within 20 meters, and decreased with distance from the index house to 6.2% in houses 80–100 meters away (

Mosquitoes, men and malaria in Kenya. A study on ecological factors affecting malaria risk

Despite various control efforts, malaria remains a major cause of illness and death on the African continent. In the near future, there may even be an increased risk of malaria as a result of changes in our natural environment, such as global warming, deforestation and urbanisation. There is an urgent need to assess the impact of these changes on malaria vector populations and malaria risk. The aim of this thesis is to elucidate mechanisms that regulate the population dynamics of malaria vectors and relate these to malaria transmission and malaria risk. Field and laboratory studies were carried out in westernKenya, where malaria seriously affects the daily life of humans. With this information, local malaria risk models will be developed that may be used to design tailor-made approaches for malaria prevention and control.Many physical, biological and socio-economic factors affect the risk of malaria. Temperature, rainfall and humidity determine mosquito survival and development, whereas the presence of mosquito breeding sites, vegetation, land-use, house construction and the use of preventive measures mainly determine vector-host contact (Chapter 2). Many of these factors are conduciveformalaria transmission in western Kenya. The local population, therefore, spends much money on malaria preventive measures and health care (Chapter 3). These costs could be averted if a good and affordable health care system is in place.Within the aquatic habitats of An. gambiae sensu lato , the main vector of malaria in sub-SaharanAfrica, larvae may be observed feeding and interacting with each other. These larvae are under a high pressure to develop to the adult stage as rapidly as possible, since their habitat may dry up within a few days if no rain falls. Nevertheless, eggs and larvae may survive on damp soil for a few days (Chapter 5). Moreover, first-instar larvae that hatch from eggs on damp soil may reach nearby water by active dispersal (Chapter 5). High densities may lead to opportunities for cannibalism and predation among larvae of An. gambiae s.l. (Chapter 6). This is mostly affected by the amount of space available, but not by the amount of food (Chapter 7). The fact that larvae aggregate (Chapter 10) or experience a decreasing habitat size if no rain falls, will probably lead to frequent interactions between larvae and thus to cannibalism and predation in the field. Using DNA-fingerprinting techniques (microsatellite markers), we found that female An. arabiensis mosquitoes may distribute their eggs over at least two sites (Chapter 8). This may be advantageous from an evolutionary perspective, since breeding sites can dry up rapidly. Our results on egg and larval survival in desiccating habitats, cannibalism and predation, and oviposition strategy suggested that these mechanisms are important determinants of vector population dynamics.African highlands are considered to be most at risk of malaria, since these areas are currently free of malaria. The local population will not have developed a protective immunity. Our studies revealed that adult vectors survive in a highland area, but the larval stages do not develop and die before pupation as a result of the cool temperatures in this area (Chapter 4). Some breeding sites of malaria vectors were found in the area (Chapter 11), but they probably contribute little to the adult vector population. Therefore, the malaria infections observed among school children in this area (Chapter 9) are probably the result of mosquitoes that disperse from lower to higher elevations, survive inside houses and infect people locally. The results suggest that a temperature increase of a few degrees may lead to outbreaks of malaria once vector populations get established in highland areas. At lower elevations, but close to the highland area, malaria risk was strikingly different with malaria being transmitted year round. Interestingly, significant temporal variation in malaria prevalence and morbidity between years was observed, probably as a result of an unusual dry period during the first study year (Chapter 9). We identified rainfall and evapotranspiration as important drivers of vector abundance and species composition (Chapter 10). The estimated number of infective bites (Entomological Inoculation Rate or EIR) could not explain malaria prevalence one or two months later, but a lower EIR during the first (dry) year of study was associated with a lower malaria prevalence and a higher morbidity.The main conclusion from this thesis is that ecological factors may cause large differences in malaria transmission and malaria risk on a relatively small spatial scale. Changes in these factors may result in epidemics in highland areas. Additionally, they may alter malaria risk in lowland areas, but further studies are required to investigate the role of immunity development in the human population. Ultimately, information gained from these studies should be integrated with remotely sensed data to develop accurate models for malaria risk assessment on a wider spatial scale