Textbook Question
The sporogonic phase of Plasmodium occurs in ___________.
a. red blood cells
b. liver cells
c. schizonts
d. Anopheles mosquitoes
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21. Principles of Disease
Stages of Infectious Disease Progression
2:05 minutesProblem 10
Textbook Question
Why are there more cases of West Nile virus encephalitis in summer than in winter of every year?
Verified step by step guidance1
Understand the transmission cycle of West Nile virus, which primarily involves mosquitoes as vectors and birds as reservoirs.
Recognize that mosquito activity is highly dependent on temperature and environmental conditions, with warmer temperatures in summer increasing mosquito breeding and biting rates.
Note that in summer, the population of mosquitoes rises significantly, leading to more opportunities for the virus to be transmitted to humans.
Consider that the virus replicates more efficiently within mosquitoes at higher temperatures, shortening the incubation period and increasing transmission potential.
Conclude that these factors combined—higher mosquito populations, increased biting activity, and faster viral replication—result in more cases of West Nile virus encephalitis during summer compared to winter.
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2mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
West Nile Virus Transmission Cycle
West Nile virus is primarily transmitted through the bite of infected mosquitoes, especially Culex species. These mosquitoes become carriers after feeding on infected birds, which serve as the virus's natural reservoir. Understanding this cycle is crucial to explain seasonal variations in infection rates.
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Mosquito Activity and Seasonal Temperature Effects
Mosquitoes are cold-blooded and their activity, breeding, and lifespan increase in warm temperatures typical of summer. Higher temperatures accelerate the virus replication within mosquitoes, leading to more frequent and intense transmission during summer months compared to winter.
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Human Exposure Patterns
During summer, people spend more time outdoors, increasing their exposure to mosquito bites. In contrast, colder winter temperatures reduce outdoor activities and mosquito populations, resulting in fewer human infections. This behavioral factor contributes to the seasonal rise in West Nile virus encephalitis cases.
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