Decease transmission by Mosquito
How Mosquitoes Transmit Diseases
Mosquitoes can transmit several diseases to humans, including malaria, dengue, chikungunya, and Japanese encephalitis. However, mosquitoes are not born carrying these diseases. They become infected only after feeding on an infected host.
The transmission of disease usually involves three stages:
The mosquito becomes infected.
The disease-causing organism develops inside the mosquito.
The infected mosquito transmits the pathogen to another person.
This process is known as vector-borne transmission.
Stage 1: How a Mosquito Becomes Infected
A mosquito becomes infected when it bites a person or animal that already carries a disease-causing organism in the bloodstream.
During a blood meal:
The mosquito inserts its mouthparts into the skin.
Blood is drawn through the labrum into the mosquito’s digestive system.
If the blood contains viruses, parasites, or other pathogens, these organisms enter the mosquito along with the blood.
At this stage, the mosquito has ingested the pathogen, but it cannot yet transmit the disease to another person.
Stage 2: What Happens Inside the Mosquito
Once inside the mosquito, the pathogen must survive and develop before it can be transmitted.
The process differs depending on the disease.
For Viral Diseases (Dengue, Zika, Chikungunya)
The virus enters the mosquito’s midgut along with the blood meal.
The virus multiplies inside the mosquito’s body.
It spreads from the gut into other tissues.
Eventually, the virus reaches the salivary glands.
This process may take several days, depending on temperature and mosquito species.
For Parasitic Diseases (Malaria)
In malaria transmission:
The mosquito ingests Plasmodium parasites from infected blood.
The parasites undergo several stages of development inside the mosquito.
They migrate through the mosquito’s body.
Finally, they accumulate in the salivary glands.
Only after this development stage can the mosquito transmit malaria.
Extrinsic Incubation Period
The time required for the pathogen to develop inside the mosquito is called the extrinsic incubation period.
During this period:
The mosquito is infected but cannot yet transmit the disease.
Once the pathogen reaches the salivary glands, the mosquito becomes infectious.
Environmental factors such as temperature and humidity can influence how quickly this process occurs.
Stage 3: Transmission to Humans
When the infected mosquito bites another person, disease transmission can occur.
During the bite:
The mosquito inserts its mouthparts into the skin.
The mosquito injects saliva into the skin to prevent blood clotting.
If the mosquito is infected, the pathogen present in the saliva enters the human bloodstream.
This is how diseases such as dengue, malaria, and chikungunya are transmitted from mosquitoes to humans.
Why Mosquitoes Are Effective Disease Vectors
Mosquitoes are particularly efficient at spreading diseases because:
They feed on blood from multiple hosts.
They live close to human settlements.
Their saliva provides a direct pathway for pathogens to enter the bloodstream.
Some mosquito species feed frequently during their lifespan.
These characteristics make mosquitoes one of the most important vectors of infectious diseases worldwide.
Important Note
Not every mosquito carries disease. Only mosquitoes that have previously bitten an infected host and completed the internal development stage of the pathogen can transmit the disease.
Controlling mosquito populations and preventing mosquito bites remain key strategies for reducing the spread of mosquito-borne diseases.
