Some viruses choose mosquitoes as their primary hosts. Even so, people still contract diseases. Entomologists and virologists explain why this happens. The human body has different organ systems, one of which defends it from foreign invaders. Yet, somehow, mosquito-borne viruses still manage to settle and infect. Read on and learn how this is possible.
Human Infection
The human body can fight off viruses. The immune system can perform such a feat. However, the body’s internal environment is stable and temperate. It is ideal for viruses to survive, thrive, and replicate. Viral infection risk also increases through frequent travel and constant contact with animals.
Arboviruses are the viruses spread by insects. It is very challenging for them to replicate well in the human body. Contracting an arbovirus from mosquitoes is usually extremely difficult.
A good example is a togavirus, which causes EEE (eastern equine encephalitis). EEE is rare, but it can result in a fatal condition that attacks the neurological system in horses and humans. It is an endemic mosquito-borne disease in the eastern United States. Recently, it has occurred in New York, Michigan, and Massachusetts.
Animals to Mosquitoes
Studies show that a female’s salivary glands and gut system create an ideal environment for viruses to thrive. The virus from a female mosquito’s bite infects an animal host. It travels to the insect’s midgut through the ingested blood. The pathogen infects the cells in the midgut to prevent the environment from ejecting it. This transmitted virus replicates in the host cells without alarming the mosquito’s immune system. The damaged cells will release the virus so that it can reach the mosquito’s salivary glands. There, the virus will wait for transmission. Every bite releases the infected saliva into the new animal host. This event continues the viral life cycle.
The primitive immune system in mosquitoes allows viruses to thrive in their tiny bodies. It can only launch a weak attack against them. As a result, an arbovirus can remain in the mosquito for a long time. It can do so without damaging the mosquito’s body. This relationship is ideal for spreading the virus.
This tolerance is the result of millions of years of evolution. The arbovirus stays and replicates. In doing so, it affects the way the mosquitoes reproduce and behave. Some viruses increase the mosquito’s attraction to infected animals. Others make the female mosquitoes look for more blood meal sources. These pathogens can reduce the number of eggs in a female mosquito. They can sterilize the mosquito or increase the development time of the eggs.
Mosquitoes to Humans
Some viruses, specifically those that come from mosquitoes, must go through a gauntlet to colonize a human body. Disease transmission is the first step. This is the easiest step the virus has to go through. When a mosquito infected with EEE bites a human, the infected saliva carries the virus. The battle begins under the individual’s skin, where the saliva remains. The virus must adapt to the body’s warm temperature of at least 37 degrees Celsius or 98.6 degrees Fahrenheit.
Next, the virus must avoid the immediate barriers in the human body, including the mucosa, skin layers, and immune cells. The human immune system will target the virus once it is in the bloodstream. Once the virus is in the central nervous system, the immune system will overreact. It will damage the nerve cells and cause inflammation. This stage can lead to long-term cognitive impairment.
Mosquitoes Persist
Surviving the host’s hostile defenses is a priority for viruses. It must mutate or shape-shift to prevent the immune system from detecting it. Another survival technique is to take over human cells and replicate in them. The virus uses the cell’s mechanisms to change how it divides. Some viruses are more adaptive than others. That is why humans still get sick despite the strong immune defenses in action.