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The Challenge of Parasite Control
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
In earlier chapters we have had occasion to mention Wolbachia: an endosymbiotic genus of bacteria that infects many insects and nematodes. Among the curious facts about these microbes is that they are transmitted vertically from female to eggs, and that for many strains they enforce cytoplasmic incompatibility on their hosts; sperm of infected males cannot successfully fertilize eggs of non-infected females. Eggs of infected females, on the other hand, can be fertilized to produce viable offspring. Furthermore, in many cases, the bacteria appear to protect their hosts from various pathogens. For example, the Aedes aegypti mosquitoes responsible for dengue transmission can be rendered resistant to the virus by infecting them with certain Wolbachia strains. The bacteria are non-pathogenic for the mosquito and infected mosquitoes efficiently pass the symbionts on to offspring. Various field trials have shown that mosquitoes carrying Wolbachia rapidly replaced those mosquitoes lacking the bacteria. Consequently, the use of dengue-resistant, Wolbachia-infected mosquitoes may provide a novel means of disease control.
Out of Nowhere
Published in Rae-Ellen W. Kavey, Allison B. Kavey, Viral Pandemics, 2020
Rae-Ellen W. Kavey, Allison B. Kavey
Traditional vector control measures like insecticides and elimination of larval breeding sites are still recommended, but one new approach involves the development of mosquitoes that are resistant to arbovirus infection. The bacterial symbiont Wolbachia has been transferred from Drosophila into the mosquito Aedes aegypti, where it blocks the transmission of arboviruses including Zika. Mosquitoes infected with Wolbachia were resistant to current circulating Zika virus isolates with reduced virus prevalence, intensity, and disseminated infection.95 A Wolbachia-infected A. aegypti mosquito has been developed and has already been shown to spread through mosquito populations after large-scale release. Wolbachia-infected mosquitoes were released in two Rio de Janeiro neighborhoods in 2014, and in a suburb of Medellín in 2015. Researchers plan to survey the insects for viral infection and track the local incidence of disease in areas with and without Wolbachia-infected mosquitoes. Proving that Wolbachia infection of wild mosquitos limits human infections will be critical before the method can find widespread use.96 A field trial in Townsville, Australia has eliminated local arbovirus disease transmission over more than 2-year follow-up.97 The World Mosquito Program is reportedly testing this approach in 12 countries.
The Diseases – Malaria, Filariasis and Dengue
Published in Jacques Derek Charlwood, The Ecology of Malaria Vectors, 2019
Wolbachia is a bacterium that affects a large number of arthropods. It has been estimated that between 20% and 70% of insect species are infected. A number of mechanisms have evolved to enhance its transmission. In some insects, the number of males produced is reduced (because it is only eggs that transfer the bacterium). In mosquitoes, due to a phenomenon known as cytoplasmic incompatibility infected males are unable to fertilise uninfected females, which then lay sterile eggs (Figure 12.17) because the cycle of mitotic division of the parental chromosomes in the first few divisions are out of sync and so division fails and the egg dies.
Wolbachia-Virus interactions and arbovirus control through population replacement in mosquitoes
Published in Pathogens and Global Health, 2023
Thomas H Ant, Maria Vittoria Mancini, Cameron J McNamara, Stephanie M Rainey, Steven P Sinkins
A large body of experimental data has been published in recent years demonstrating the virus-inhibiting effect that Wolbachia can confer on host insects (see Table 1). This antiviral effect appears to be primarily active against viruses with a positive-sense single-stranded RNA genome [(+)RNA], which includes the mosquito-borne viruses most important to public health (dengue, Chikungunya, Zika, Yellow fever, West Nile etc.). Although an overwhelming majority of studies indicate that some combinations of host species and Wolbachia strain result in an inhibitory effect on viral replication (likely in part a reflection of a bias in the use of (+)RNA human arboviral pathogens in research studies), a small number of reports suggest that Wolbachia can in some circumstances enhance host susceptibility to infection with certain viruses. There is substantial divergence in insect host species and virus phylogeny examined in the various Wolbachia-virus interaction studies, as well as differences in experimental methodology, ranging from purely correlative studies to those with controlled laboratory infectious bloodmeal challenges. Among the laboratory studies, there is significant variation in the methods used to deliver virus, quantify virus, and even in the nature of the Wolbachia transinfection (e.g. stable germline or transient somatic infection). As any potential for viral enhancement is of clear public health importance for the use of Wolbachia in vector control, claims of enhancement should be closely examined and any implications carefully considered.
Oxitec and MosquitoMate in the United States: lessons for the future of gene drive mosquito control
Published in Pathogens and Global Health, 2021
Cynthia E. Schairer, James Najera, Anthony A. James, Omar S. Akbari, Cinnamon S. Bloss
The MosquitoMate product takes advantage of an observed incompatibility between mosquitoes infected and uninfected with Wolbachia bacteria [4,5]. This approach releases infected male mosquitoes into the environment to mate with wild (uninfected) females. Eggs produced by these pairings often do not hatch, thus reducing the total population of mosquitoes. Such a system of mosquito control relies on the ability to reliably sort infected males from infected females before release because infected males and females can successfully reproduce Wolbachia-infected offspring. If too much of the wild population of mosquitoes is infected with Wolbachia the technique will no longer be effective. Therefore, the major technical challenge of Wolbachia systems is reliably sorting lab-raised mosquitoes at scale. Such a system has been developed in partnership by MosquitoMate and Verily [1].
The relevance of studying insect–nematode interactions for human disease
Published in Pathogens and Global Health, 2022
Zorada Swart, Tuan A. Duong, Brenda D. Wingfield, Alisa Postma, Bernard Slippers
Bacteria often play a role in nematode–insect interactions. Heterorhabditis and Steinernema coevolved with bacteria in the genera Photorhabdus and Xenorhabdus to become virulent insect pathogens [27,28]. Although axenic nematodes are able to infect and kill an insect host [29,30], bacterial symbionts contribute to killing the host, digesting host tissues, and preventing other micro-organisms from colonizing the carcass [31]. In the case of parasitic nematodes causing human diseases such as filariasis, an intracellular endosymbiont, Wolbachia, is involved in the nematode’s survival and reproduction [5,32]. Furthermore, Wolbachia also influences many aspects of insect biology, either as a mutualist or as a pathogen [33,34].