We look forward to summer months as this is the time of the year we like enjoy our time in the sun. But, these months are also notoriously known for the increase in mosquito borne diseases like the Ross River fever and dengue fever.
Travelers from Australia venturing through Southeast Asia are also exposed to dangerous mosquito-borne viruses like chikungunya virus and Japanese encephalitis. If these diseases successfully establish themselves in Australia, it will be a major health concern. The impact can be far reaching and can impact the economy, tourism and way of life. In the recent times, there has been an expansion in outbreak of mosquito-borne the diseases, both globally and within Australia. Increased urbanization, increased travel, trade and changing climate contribute to it as it enhances the suitability of environments for mosquitoes.
Extensive research are going on globally to identify treatments to protect people from the tiny beasts, however none have been clinically approved for use to date. A dengue vaccine (Dengvaxia) was approved for use in Mexico, Brazil and the Philippines last December, but its effectiveness is still a question mark. Mosquito population control measures have been effective for a limited time only. As per an estimate from WHO, some 390-million dengue infections occur annually, of which 100-million people fall ill leading to some 25,000 deaths.
The need for alternate means to control these deadly diseases is urgent. Recently, mosquitoes infected with Wolbachia bacteria have been used to dramatically reduce the potential of mosquito population to transmit dengue infections. Field trials are underway in Australia, China, Vietnam, Brazil and Thailand, and the results so far have been promising. However, the long-term success and effectiveness against other infections still need to be tested.
In an innovative step, Oxitec – a British biotech company, has altered the DNA of male mosquitoes such that offspring die as larvae or pupae. Some other laboratories have experimented to ensure that only male mosquitoes are produced, so that the entire population collapses. Only further field tests can validate the effectiveness and ecological impact of such measures.
The threat is from female mosquitos only as only they bite people or animals to obtain the blood proteins needed to develop and lay their eggs. When these female mosquitoes bite an infected being, the virus enters their gut via the blood-meal and infects them too. The virus gets transmitted further when these infected mosquitoes bite another susceptible host.
It is interesting to note that the viruses which can cause severe disease in people have no physical ill-effects on the infected mosquito. It seems that mosquitoes are capable of protecting themselves against disease when infected by these serious viruses. If we delve deeper into how it happens, it may provide important insights that will enable the development of new disease intervention strategies.
In a research last year that used an RNA-sequencing approach a number of genes from multiple cellular pathways that play integral roles in protecting mosquitoes from the viruses they carry were identified by the researchers. Previous researches had identified a new protein Vago that showed the ability to restrict the spread of viral infection in mosquitoes. In another recent research, it was shown that a virus increases production of a mosquito gene, Cullin4, which shuts down the immune response of mosquitoes by blocking the action of Vago. It lets the virus to multiply in mosquitoes and be transmitted to the next person.
It is for the first time that the existence of an immune evasion mechanism has been demonstrated in mosquitoes or any other insect. These results provide new insights into how virus reproduces in mosquitoes. It has also provided us with a large dataset of mosquito genes, which play a role during the infection process. These findings show that it is possible to reduce a mosquito’s capacity to transmit viruses by manipulating its immune system.
Even though the mosquitoes spread viruses and infections, they are necessary evil as they act as pollinators as well as food source for birds and fish. So, instead of suppressing the mosquitoes, a better approach is to make them resistant to infection. This can be done by increasing production of antiviral proteins or decreasing production of proteins that help viral growth. Another way is to block entry of the virus into the mosquito by modifying proteins present in its gut.
Gaps in our understanding of the complex relationship between mosquitoes, viruses, people and the environment need to be investigated to use the information in preventing the spread of disease.