Wolbachia bacteria infect a wide variety of arthropods (such as insects, spiders, crustaceans) and nematodes. Wolbachia is a symbiotic bacterium that lives inside the cells of its host. It mainly affects and manipulates the reproductive tissues – testes and ovaries of the host. Applications of Wolbachia bacteria hold great potential for human benefits.
The symbiotic relationship of the Wolbachia bacteria with the arthropods and nematodes can be exploited for the control and treatment of certain infectious diseases.
Wolbachia, male-hating bacteria affects the birth and development of male hosts. It can only spread from one generation to the next by invading a female’s eggs.
It can wipe off the male host with efficient strategies that range from forced sex change to male-killing.
Applications of Wolbachia
Applications of Wolbachia bacteria are of significant importance as they can be used in the control of certain infectious diseases.
Certain communicable diseases enduring in the tropical and subtropical conditions are compiled as Neglected tropical diseases (NTDs) by the WHO.
Cutaneous filariasis (onchocerciasis, commonly known as river blindness), lymphatic filariasis (elephantiasis), Dengue and chikungunya are some of the debilitating diseases that come under the NTDs. Those diseases affect more than one billion people costing huge economic burdens every year.
Wolbachia bacteria hold great potential to resolve a wide variety of human diseases.
1. Wolbachia in Filarial infections
Many species of filarial nematodes including Wuchereria bancrofti and Brugia malayi, causing lymphatic filariasis, Onchocerca volvulus causing onchocerciasis host Wolbachia bacteria in their tissues in all their lifecycle stages.
These nematodes require Wolbachia bacteria for their fertility, development, and survival. Therefore, Wolbachia provides a target for filariasis control.
The anti-filarial drugs currently available are effective only against the larval forms of the parasite. These drugs are not effective against adult worms. The adult worms can survive in humans for more than 10 years, because of that annual administration of the drugs on a community scale are required.
The depletion of Wolbachia bacteria in filarial nematodes by antibiotics can kill the adult worms.
Antibiotics capable of depleting Wolbachia bacteria could be a promising therapeutic strategy to control the filarial infections as the Wolbachia bacteria are required for the filarial nematodes.
2. World mosquito program
The applications of Wolbachia in insect vector control provides great potential for controlling mosquito-borne diseases such as malaria, dengue, chikungunya, etc.
The Aedes aegypti mosquito is the main transmitter of dengue, Zika, chikungunya, and yellow fever viruses.
Mosquitoes do not naturally carry the virus, they are just vectors. They pick up the virus when they bite the infected people and transmit it to the next person.
Wolbachia bacteria live inside the mosquitoes and take up all the resources that make it harder for viruses like dengue, Zika, chikungunya, and yellow fever to grow and replicate inside the mosquitoes.
If the virus cannot replicate and increase in numbers inside the mosquito, then it is less likely to spread viruses from person to person.
However, Aedes aegypti mosquitoes don’t normally carry Wolbachia, though many other mosquitoes do.
So, at the World Mosquito Program, the mosquitoes were infected with Wolbachia and the Wolbachia-carrying mosquitoes are released into areas affected by mosquito-borne diseases.
Furthermore, Wolbachia can decrease the lifespan of Aedes aegypti mosquitoes.
Is this genetic modification?
The Wolbachia method is not considered as genetic modification. It is a biological control, where one species is used to control the other species, Wolbachia controlling the spread of the virus.
Wolbachia can manipulate the host biology
Wolbachia manipulate its host’s biology mainly by four strategies. They are,
- Male killing
- Cytoplasmic incompatibility
1. Male killing
Wolbachia bacteria hate the male hosts, that it kills the infected males during the larvae development and thereby increases the number of infected females.
For example, in species such as ladybirds, flour beetles, and fruitfly, Wolbachia simply kills males during their early development.
A study demonstrated that the Wolbachia presence and male-killing in two species, the two-spot ladybird Adalia bipunctata, and the butterfly Acraea encedon.
Wolbachia not just kills its male host, it causes induced sex change.
For instance, Wolbachia attribute to the feminization of genetic males in the bug Armadillidium vulgare.
In the case of Zyginidia pullula, a leafhopper, the infected and uninfected female leafhoppers are morphologically indistinguishable. However, the feminized males have an intersex phenotype and the degree of feminization was correlated with the Wolbachia density in the host tissues.
Parthogenesis is defined as the process in which females reproduce without fertilizing with the males.
It is observed in the Wolbachia infected arthropods. Infected female hosts are reproduced without the males. Eg Trichogramma parasite
Antibiotics treatment could cure parthogenesis in the Trichogramma
4. Cytoplasmic incompatibility
Cytoplasmic incompatibility is defined as the inability of infected males to successfully reproduce with uninfected females or females infected with another strain of Wolbachia.
In mosquitoes, for instance, Wolbachia alters the cells by an unknown mechanism so that the sperm can only fertilize eggs that contain the same Wolbachia strain. This decreases the reproduction among uninfected females, therefore driving the infection through the population with each generation.
Wolbachia induced cytoplasmic incompatibility is also observed in beetles, wasps, etc.
Wolbachia bacteria can manipulate its host biology and can be applied in large public health programs to control the insect vectors and to treat filarial infections.
Though Wolbachia bacteria do infect humans and animals, it is desirable to study and closely monitor the application programs to ensure safety and success as well as to predict any negative outcomes.