ABSTRACT
Wolbachia are obligate symbionts that live in vacuoles inside the cells of their host. Infections are passed on vertically in the egg cytoplasm, from infected mothers to their offspring. Wolbachia are one of the notable pandemics of life from a biodiversity standpoint because they are estimated to occur in millions of invertebrate species, together with 40% of all arthropod species. Wolbachia are obligate endosymbiotic a-proteobacteria that are most closely linked to the genera Ehrlichia and Anaplasma. They are pleiomorphic, stretching from 0.2 to 4µm in size, and exist in an obligate intracellular niche inside host-derived vacuoles. Wolbachia are transmitted mainly maternally through the egg cytoplasm, even though paternal or horizontal transmission may also happen at a low rate. The bacteria genus was first identified in 1924 through collaborative work between Marshall Hertig, an entomologist, and Simeon Burt Wolbach, a pathologist, in their study of the common house mosquito (Culexpipiens). The Wolbachia bacteria species are taxonomically classified under the domain Bacteria, phylum Proteobacteria, class Alphaproteobacteria, order Rickettsiales, family Anaplasmataceae, tribe Wolbachieae, and genus Wolbachia; they belong to about 17 phylogenetic clades called supergroups (A to Q) found in arthropod and nematode hosts. The use of Wolbachia for sterile insect technique (SIT) and gene drives is fairly simple for producing transgenic vectors and noninvasive populations. While different insect species are naturally infected with specific strains of Wolbachia, other species are naturally uninfected. For Culexpipiens and Aedesalbopictus, almost all species harbor Wolbachia; Anopheles species and Aedes aegypti have been generally found to be uninfected. The error rate and efficiency of Wolbachia gene drives depend on whether we always get the intended outcome of cytoplasmic incompatibility (CI). The ability of Wolbachia to induce CI is pivotal in implementing the two major Wolbachia-based vector control strategies: to reduce the population size of Wolbachia host vectors or decreasing population density in a locality by killing individuals and arresting reproduction processes and to change the population with undesirable characteristics such as spreading diseases by gradually replacing them with individuals without such negative traits. Wolbachia gene drives have very little effect on ecosystems, as there is no release of any substance that may affect other unintended species. Wolbachia gene drives are fairly easy to design and implement as well. Various projects have been deployed, including the World Mosquito Program (WMP) in various countries all over the world, such as in Australia, Vietnam, Colombia, and Brazil, to take advantage of Wolbachia in combating vector-borne diseases through population modification and suppression. Wolbachia has also been acknowledged to prevent the replication of the chikungunya virus (CHIKV) in A. aegypti.
