The Challenge of Parasite Control
Eric S. Loker, Bruce V. Hofkin in Parasitology, 2023
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.
Evolutionary Biology of Parasitism
Eric S. Loker, Bruce V. Hofkin in Parasitology, 2015
Interestingly, once again mate choice may come into play here as there is evidence from Drosophila hosts that, not surprisingly, uninfected females are strongly selected to avoid mating with Wolbachia-infected males. Furthermore, there is even a possibility of involvement of another magic trait, as the symbionts in some cases are known to produce odors that act as sex attractants for their hosts. Although it may remain arguable if Wolbachia infections actually lead to host speciation, it is less arguable that in a broader sense they clearly contribute to reproductive isolation and thus favor the possibility of host speciation. It is noteworthy too that other organisms beside Wolbachia can cause CI and potentially favor isolation of host populations. In general, we need remain mindful of the possibility of symbiont-mediated effects on host speciation.
Communicable diseases
Liam J. Donaldson, Paul D. Rutter in Donaldsons' Essential Public Health, 2017
The most recent developments involve research and field studies to release genetically modified male mosquitoes that pass on a mutation when reproducing so that the resulting eggs are fatally flawed. This has caused concerns about unforeseen circumstances, but trials are underway. Another novel approach involves introducing a bacterium Wolbachia that is found within the cells of a high proportion of insects, including mosquitoes (although not those that transmit malaria or dengue fever). The relationship between the bacterium and the insect is not fully understood but is symbiotic or parasitic rather than pathogenic. It appears to influence the host’s reproductive processes and to protect against viral infection. Scientists are seeking to introduce Wolbachia into the bodies of A. aegypti mosquitoes in ways that will make them resist the dengue virus.
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].
Related Knowledge Centers
- Bacteria
- Mutualism
- Ovary
- Parasitism
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- Reproductive System
- Pleomorphism
- Gram Stain
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