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Wolbachia is a bacterium that lives only within insect cells and is passed from one generation to the next through the insect’s eggs. It is present in up to 70% of all the different species of insects around us including some mosquitoes that bite people but not the major mosquito species involved in the transmission of diseases such as dengue and malaria.

For many years now scientists have been studying Wolbachia looking for ways to utilise the bacterium to potentially control the mosquitoes that spread human diseases.

Wolbachia pipientis was first observed in the ovaries and testes of the mosquito, Culex pipiens in the 1920’s. Early studies showed that it was not a pathogen of mammals but instead a naturally occurring and harmless symbiotic bacterium of insects. Since those early studies it has since been determined that it is extremely common in insects, with estimates suggesting that 60-70% of all insect species naturally carry different strains of Wolbachia. Considering that there may be 2-5 million different insect species on the planet Wolbachia is a very successful and pervasive insect bacterium. 

The diagram above explains Cytoplasmic Incompatibility and how by releasing a limited number of mosquitoes with Wolbachia to breed with wild type mosquitoes, over a small number of generations, will result in all the mosquitoes having Wolbachia.

a)  When male mosquitoes with Wolbachia mate with female wild mosquitoes that don’t have Wolbachia those females will have eggs but they won’t hatch.

b)  When male mosquitoes with Wolbachia mate with females that are already carrying Wolbachia the mating will be normal and the offspring will all have Wolbachia.

c)  When female mosquitoes with Wolbachia mate with males without Wolbachia all her offspring will have Wolbachia.

Many different strains of Wolbachia

Eliminate Dengue is currently field-testing two Wolbachia strains - wMel and wMelPop - with other Wolbachia strains in different stages of development.

Each strain has a slightly different effect on the mosquito’s fitness and consequently how easily it will establish in the wild mosquito population once it is released. Wolbachia strains also differ in terms of their ability to block dengue virus inside the mosquito. Over time we hope to select strains that have a strong blocking effect on dengue virus in the mosquito and therefore prevent dengue transmission and yet are easily introduced into mosquitoes in the field and thereby provide a low-cost, long-term solution to dengue control.



Bacillus thuringiensis israelensis (Bti) for the control of dengue vectors: systematic literature review


To systematically review the literature on the effectiveness of Bacillus thuringiensis israelensis (Bti), when used as a single agent in the field, for the control of dengue vectors.


Systematic literature search of the published and grey literature was carried out using the following databases: MEDLINE, EMBASE, Global Health, Web of Science, the Cochrane Library, WHOLIS, ELDIS, the New York Academy of Medicine Gray Literature Report, Africa-Wide and Google. All results were screened for duplicates and assessed for eligibility. Relevant data were extracted, and a quality assessment was conducted using the CONSORT 2010 checklist.


Fourteen studies satisfied the eligibility criteria, incorporating a wide range of interventions and outcome measures. Six studies were classified as effectiveness studies, and the remaining eight examined the efficacy of Bti in more controlled settings. Twelve (all eight efficacy studies and 4 of 6 effectiveness studies) reported reductions in entomological indices with an average duration of control of 2–4 weeks. The two effectiveness studies that did not report significant entomological reductions were both cluster-randomised study designs that utilised basic interventions such as environmental management or general education on environment control practices in their respective control groups. Only one study described a reduction in entomological indices together with epidemiological data, reporting one dengue case in the treated area compared to 15 dengue cases in the untreated area during the observed study period.


While Bti can be effective in reducing the number of immature Aedes in treated containers in the short term, there is very limited evidence that dengue morbidity can be reduced through the use of Bti alone. There is currently insufficient evidence to recommend the use of Bti as a single agent for the long-term control of dengue vectors and prevention of dengue fever. Further studies examining the role of Bti in combination with other strategies to control dengue vectors are warranted.


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