What is the most likely cause of encephalitis in a man who has been working in a garden with a lot of dead birds and high mosquito populations?

The correct answer is West Nile virus, which is known to be transmitted through mosquito bites. In the scenario described, the presence of high mosquito populations in a garden environment where there are dead birds creates a significant risk for such transmission. West Nile virus is often found in birds, which serve as reservoirs for the virus. When mosquitoes feed on infected birds, they can then transmit the virus to humans through their bites, leading to encephalitis, which is an inflammation of the brain.

Encephalitis can result from various viral infections; however, the combination of dead birds and mosquitoes strongly points to West Nile virus as the likely cause. Other viruses listed are less associated with this specific environmental exposure. Epstein-Barr virus is known for causing infectious mononucleosis and does not primarily cause encephalitis through this route. Parvovirus mostly causes mild illness and is typically associated with other clinical conditions, not encephalitis. Hantavirus primarily causes respiratory illness and is transmitted through rodent droppings, not birds or mosquitoes, making it an unlikely culprit in this case. Therefore, the presence of dead birds and mosquitoes directly implicates West Nile virus as the most probable cause of encephalitis in this scenario.