Screening of starving Mosquitoes: Spreading Infectious Diseases From Gut Fluid

Author Name(s): *Amol T. Tande, Gaurav M. Alande, Nurzeba M. Bepari, Abhinandan R Patil, John I D'souza
Author Email: attande.tkcp@gmail.com

Abstract

Mosquitoes act as vectors for transmission of many diseases since long period of time. Blood-feeding mosquitoes are much neater and more surgical; they insert a tube (proboscis) for drawing blood, by the time they are ready for their next meal, even on a second host after an interrupted meal, any bacteria or/and viruses from their first meal are safely stored away in their midgut. In the second mechanism, a mosquito would initiate the cycle by beginning to feed on any community disease carrier and be interrupted after it had successfully drawn blood. Instead of resuming the partial blood meal on its original host, the mosquito would select any disease free person to complete the meal. As it penetrates the skin of the new host, the mosquito would transfer virus/ bacteria particles that were adhering to the mouthparts from the previous meal. However, studies conducted by the CDC (centre for disease control and prevention) and elsewhere have shown no evidence of HIV transmission from mosquitoes. Lack of such outbreaks, despite intense efforts to detect them, supports the conclusion that HIV is not transmitted by insects as per CDC. Mosquitoes collected from local area at Warana valley were in larvae forms, which were kept in starving condition at artificial water hub. The quantities of gastro tract (fluid content/carrying capacity) of mosquitoes were evaluated by microtitration method; made in progress by sacrificing the vector. The vector nature of the same was verified by transfer of Lactobacillus casein (non pathogenic) bacteria from mosquitoes to microbial media of MRS (deMan Rogosa and Sharpy Media); where the bacteria get flourished acting as biomarker. The transfer of Lactobacillus casein at starvation made matter of concern in transfer of bacterial disease and even AIDS positive viruses.

Introduction

The mosquito’s digestive system is a closed system, with one long enclosed tube (alimentary canal) running lengthwise through the body. The alimentary canal is a one way street– food enters the mouth and gets processed as it travels toward the anus. Each of the three sections of the alimentary canal performs a different process of digestion.
Trypsin is synthesized less than 4 hours after the blood meal, but it is the “late trypsin”, synthetized between 8 and 24 hours after the meal, which represents the major endoprotease involved in bloodmeal digestion. These enzymes play a role in parasite transmission and it has been shown that ookinete development is impaired after artificially feeding a mosquito on infected blood and trypsin inhibitors. The peritrophic membrane (PM) is an acellular sac produced by the cells lining the midgut, in response to food ingestion. It consists of proteoglycans and chitin. The PM completely surrounds the food bolus and contributes to the digestive process by compression. The role of the PM is not entirely clear: (1) act as physical protection against pathogens, (2) act as a filter for blood components, and (3) act as a barrier to avoid clogging the spaces between the microvilli of the epithelium.
Malaria parasites have to complete their development, including mating and differentiation of ookinete, before the PM has reached maximum rigidity. To achieve this, the parasites have evolved mechanisms to penetrate the PM and traverse the gut to continue their development. The most important of these mechanisms is the secretion of a chitinase. The mosquito digestive system helps in this process, since the chitinase is actually secreted as an inactive enzyme which is activated by mosquito serine proteases.
When AIDS was first recognized, there were many newspaper reports on the possibility of mosquitoes being involved in its transmission. Almost half of 6625 men and women interviewed in Zaire in 1988 to determine existing levels of knowledge regarding AIDS believed in the transmission of AIDS by mosquitoes. A recent survey involving 1500 high school students (grade 10) from 14 schools in 4 different provinces in Papua New Guinea revealed that more than a third of them (34%) considered mosquitoes to be carriers of HIV. Although mosquitoes are known to be vectors of certain death-threatening viral diseases such as yellow fever, dengue fevers. We review the theoretical mechanisms which would allow blood-sucking insects such as mosquitoes to transmit virus and discuss the evidence against the transmission of HIV by mosquitoes.
Theoretical mechanisms for the possible transmission of HIV by mosquitoes:
I. Biological transmission: A mosquito feeding on a person infected with HIV could ingest the virus which then undergoes multiplication within the mosquito and migrates to its salivary glands. When the infected mosquito seeks a second blood-meal from an uninfected person, it could transfer the HIV from its salivary gland during the course of feeding. This is the mechanism involved in the transmission of yellow fever and dengue.

II. Mechanical transmission: Human defensive behaviour may prevent a partially blood-fed mosquito from completing a blood-meal on a person infected with HIV. However, instead of resuming feeding on the same person the mosquito may select an uninfected person to complete it’s feeding on. As it penetrates the skin of the new host, the mosquito could transfer HIV particles that were adhering to the mouthparts from the previous partial blood-meal. This is purely mechanical transmission because the virus does not undergo any multiplication or development in the mosquito.
Transmission through mosquito squashes:
Squashing mosquitoes is thought of by many people as an instinctive reaction triggered by the sight of the creatures on human skin. A mosquito that had had a partial blood-meal from an HIV carrier and resumed feeding on an uninfected person may be squashed into a cut in the skin. Viral infection could be initiated in this way depending on the quantity of viral particles contained in the partial blood-meal. For the cultivation of the mosquito flora mimicking and starving mosquitoes are needed. GI content of the starving mosquito if microtitrated along with the microbial assay will reveal the vector properties of the mosquitoes.

Conclusion

Mosquitoes act as vectors for various organisms. These vectors collected from local area at Warana valley were obtained in larvae forms; these forms gave the virgin vectors for the study. These vectors kept in starving condition were alive in hub containing mixture of 0.01N HCl and bacteria (Lactobacillus casein) in water. HCl was used as biomarker which did not affect the study. The quantities of gastro tract (fluid content/carrying capacity) of mosquitoes were evaluated by microtitration method; made in progress by sacrificing the vector. The vector nature of the vector was verified by transfer of Lactobacillus casein (non pathogenic) bacteria from mosquitoes to microbial media of MRS (deMan Rogosa and Sharpy Media). These bacterial loads were easily flourished in MRS Media. The transfer of Lactobacillus casein at starvation gave evidence that shift of bacterial disease occur easily from mosquitoes to host. This also arrives the question of transfer of AIDS positive viruses from vector to host.

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