Modelling parasitism and predation of mosquitoes by water mites

The Biodiversity of Water Mites That Prey on and Parasitize Mosquitoes

Water mites form one of the most biodiverse groups within the aquatic arachnid class. These freshwater macroinvertebrates are predators and parasites of the equally diverse nematocerous Dipterans, such as mosquitoes, and water mites are believed to have diversified as a result of these predatory and parasitic relationships. Through these two major biotic interactions, water mites have been found to greatly impact a variety of mosquito species. Although these predatory and parasitic interactions are important in aquatic ecology, very little is known about the diversity of water mites that interact with mosquitoes. In this paper, we review and update the past literature on the predatory and parasitic mite–mosquito relationships, update past records, discuss the biogeographic range of these interactions, and add our own recent findings on this topic conducted in habitats around the Laurentian Great Lakes. The possible impact on human health, along with the importance of water mite predator–prey dynamics in aquatic food webs, motivates an increase in future research on this aquatic predator and parasite and may reveal novel ecological functions that these parasitic and predator–prey relationships mediate.

[Mosquito microbiota and its influence on disease vectorial transmission]

Mosquitoes (Diptera: Culicidae) are found worldwide. Around 100 among 3500 mosquito species are known to be vectors of parasites and viruses, responsible for infectious diseases including malaria and dengue. Mosquitoes host diverse microbial communities that influence disease transmission, either by direct interference or via affecting host immunity and physiology. These microbial communities are present within diverse tissues, including the digestive tract, and vary depending on the sex of the mosquito, its developmental stage, and ecological factors. This review summarizes the current knowledge about the mosquito microbiota, defined as a community of commensal, symbiotic or pathogenic microbes harboured by a host. We first describe the current knowledge on the diversity of the microbiota, that includes bacteria, fungi, parasites and viruses and on its modes of acquisition throughout the mosquito life cycle. We then focus on microbial interactions within the mosquito gut, which notably affect vector competence, and on host-microbe interactions affecting mosquito fitness. Finally, we discuss current or potential methods based on the use of microbes or microbial products to interfere with pathogen transmission or to reduce mosquito lifespan and reproduction.

Heterogeneities in dengue spatial-temporal transmission in Brazilian cities and its influence on the optimal age of vaccination

Background

The development of a safe and effective vaccine is considered crucial for dengue transmission control since vetor control has been failed; some potential candidates are currently in test, and in this context theoretical studies are necessary to evaluate vaccination strategies such as the age groups that should be vaccinated, the percentage of the population at risk, and the target geographic regions to make dengue control feasible and optimal.

Methods

A partial differential model is used to mimics dengue transmission in human population in order to estimate the optimal vaccination age, using data collected from dengue reported cases in ten cities of Brazil from 2001 to 2014. For this purpose, the basic reproduction number of the disease was minimized assuming a single-dose vaccination strategy, equal vaccine efficacy for all circulating serotypes, and no vaccine failure. Numerical methods were used to assess the optimal vaccination age and its confidence age range.

Results

The results reveal complex spatial-temporal patterns associated to the disease transmission, highlighting the heterogeneity in defining the target population for dengue vaccination. However, the values obtained for the optimal age of vaccination, as targeting individuals under 13 years old, are compatible with the ones reported in similar studies in Brazil. The results also show that the optimal age for vaccination in general does not match with the age of the highest number of cases.

Conclusions

The variation of the optimal age for vaccination across the country reflects heterogeneities in dengue spatial-temporal transmission in Brazilian cities, and can be used to define the target population and cities to optimize vaccination strategies in a context of high cost and low quantity of available vaccine.

Vector-borne disease risk indexes in spatially structured populations

There are economic and physical limitations when applying prevention and control strategies for urban vector borne diseases. Consequently, there are increasing concerns and interest in designing efficient strategies and regulations that health agencies can follow in order to reduce the imminent impact of viruses like Dengue, Zika and Chikungunya. That includes fumigation, abatization, reducing the hatcheries, picking up trash, information campaigns. A basic question that arise when designing control strategies is about which and where these ones should focus. In other words, one would like to know whether preventing the contagion or decrease vector population, and in which area of the city, is more efficient. In this work, we propose risk indexes based on the idea of secondary cases from patch to patch. Thus, they take into account human mobility and indicate which patch has more chance to be a corridor for the spread of the disease and which is more vulnerable, i.e. more likely to have cases?. They can also indicate the neighborhood where hatchery control will reduce more the number of potential cases. In order to illustrate the usefulness of these indexes, we run a set of numerical simulations in a mathematical model that takes into account the urban mobility and the differences in population density among the areas of a city. If we label by i a particular neighborhood, the transmission risk index (TRi) measures the potential secondary cases caused by a host in that neighborhood. The vector transmission risk index (VTRi) measures the potential secondary cases caused by a vector. Finally, the vulnerability risk index (VRi) measures the potential secondary cases in the neighborhood. Transmission indexes can be used to give geographical priority to some neighborhoods when applying prevention and control measures. On the other hand, the vulnerability index can be useful to implement monitoring campaigns or public health investment.

Increased efficiency in the second-hand tire trade provides opportunity for dengue control

Dengue fever is increasing in geographical range, spread by invasion of its vector mosquitoes. The trade in second-hand tires has been implicated as a factor in this process because they act as mobile reservoirs of mosquito eggs and larvae. Regional transportation of tires can create linkages between rural areas with dengue and disease-free urban areas, potentially giving rise to outbreaks even in areas with strong local control measures. In this work we sought to model the dynamics of mosquito transportation via the tire trade, in particular to predict its role in causing unexpected dengue outbreaks through vertical transmission of the virus across generations of mosquitoes. We also aimed to identify strategies for regulating the trade in second-hand tires, improving disease control. We created a mathematical model which captures the dynamics of dengue between rural and urban areas, taking into account the movement and storage time of tires, and mosquito diapause. We simulate a series of scenarios in which a mosquito population is introduced to a dengue-free area via movement of tires, either as single or multiple events, increasing the likelihood of a dengue outbreak. A persistent disease state can be induced regardless of whether urban conditions for an outbreak are met, and an existing endemic state can be enhanced by vector input. Finally we assess the potential for regulation of tire processing as a means of reducing the transmission of dengue fever using a specific case study from Puerto Rico. Our work demonstrates the importance of the second-hand tire trade in modulating the spread of dengue fever across regions, in particular its role in introducing dengue to disease-free areas. We propose that reduction of tire storage time and control of their movement can play a crucial role in containing dengue outbreaks.

A Critical Review of All Known Published Records for Water Mite (Acari: Hydrachnidiae) and Mosquito (Diptera: Culicidae) Parasitic Associations From 1975 to Present

All published records of water mite-mosquito parasitic associations since Gary R. Mullen's comprehensive review in the 1970s of the literature were critiqued to provide an up-to-date account on the identity of water mites parasitizing mosquitoes and their geographic distribution. In total, 321 records in 62 sources were identified, with each record representing an association specific to a state, province, or region within a country. The greatest number of records were from the United States (120), followed by India (106) and Canada (40). In all, 105 species of mosquitoes were parasitized, with the majority belonging to the genera Aedes sensu lato (30), Anopheles (30), and Culex (21). Records were biased toward mosquito genera with the greatest number of freshwater species and medical importance. Most water mites belonged to the genus Arrenurus, or were Parathyas barbigera (Viets 1908). Arrenurus water mites were often not identified to species, but 15 different Arrenurus species were determined in 119 records. All but one of the species (i.e., Arrenurus madaraszi Daday 1898) were only reported from Canada, Germany, or the United States. Although a greater proportion of sources reviewed by us compared with Mullen's review identified water mites down to the level of genus, to better understand the biological significance of mite and mosquito interactions, more of an effort is needed to identify the species of water mites. The availability of molecular techniques such as DNA barcoding will make this goal more attainable.

Hyperparasitism of mosquitoes by water mite larvae

Hyperparasitism of ectoparasitic water mite larvae on mosquitoes is still a neglected relationship and was investigated only in a few studies. We analysed 2313 female mosquitoes from six different sampling localities with regard to their degree of parasitism with water mite larvae. In total, we found 38 mosquito individuals parasitized by 93 water mite larvae, ranging from 1 to 12 larvae per mosquito. Water mite larvae detected are members of the two species Parathyas cf. barbigera (n = 92) and Arrenurus cf. globator (n = 1). Out of the analysed mosquitoes, individuals out of the species Aedes vexans, Anopheles claviger, Ochlerotatus communis, the Ochlerotatus cantans/annulipes group, Ochlerotatus cataphylla and Ochlerotatus sticticus were tested to be parasitized by water mite larvae. The highest prevalence was found within the species Oc. cataphylla (28.6 %) and Oc. cantans/annulipes (21.7 %). No water mite larvae were found, e.g. on individuals of Aedes cinereus, Coquillettidia richiardii, the Culex pipiens/torrentium group, Ochlerotatus caspius, Ochlerotatus dorsalis or Ochlerotatus punctor. All of the attachment sites were located between the neck and abdomen with the ventral thorax site being the most frequent one.