1. Explain the process of the slow release replication cycle. How would this app
ID: 152062 • Letter: 1
Question
1. Explain the process of the slow release replication cycle. How would this appear on a growth plate streaked with bacteria infected by the virus?
2. West Nile Virus is the most common mosquito-borne disease in the US. In 2012, an outbreak of 5,675 human cases of the virus were reported nationwide. 1,868 cases of these were reported in Texas. In 2017, West Nile Virus was identified in mosquitoes in the Westlake area.
a. What could be done to minimize outbreaks of this disease? Why would it be effective?
b. How did environmental changes lead to the emergence of West Nile Virus in New York in 1999?
Explanation / Answer
1. The viral replication cycle usually results in death and lysis of the host cell but the slow release replication cycle does not kill the host and host slowly releases virus particles. Many viral particles are released when the cell bursts open (lysis) or by slow leakage. Replication is dependent on host cell machinery. Stages of the lytic replication cycle are:
2. a, i) Effective prevention of human WNV infections depends on the development of comprehensive, integrated mosquito surveillance and control programmes in areas where the virus occurs.
ii) Studies should identify local mosquito species that play a role in WNV transmission, including those that might serve as a “bridge” from birds to human beings.
iii) Emphasis should be on integrated control measures including source reduction (with community participation), water management, chemicals, and biological control methods.
iv) Health-care workers caring for patients with suspected or confirmed WNV infection, or handling specimens from them, should implement standard infection control precautions. Samples taken from people and animals with suspected WNV infection should be handled by trained staff working in suitably equipped laboratories.
v) Since WNV outbreaks in animals precede human cases, the establishment of an active animal health surveillance system to detect new cases in birds and horses is essential in providing early warning for veterinary and human public health authorities. In the Americas, it is important to help the community by reporting dead birds to local authorities.
Vaccines have been developed for horses. Treatment is supportive and consistent with standard veterinary practices for animals infected with a viral agent. So, it would be effective.
In the absence of a vaccine, the only way to reduce infection in people is by raising awareness of the risk factors and educating people about the measures they can take to reduce exposure to the virus.
Public health educational messages should focus on the following:
b. Temperature was found to be among the most important variables in predicting the distribution of WNV in New York in 1999. The warm temperature was associated statistically with higher human infection risk, with the virus spread into western states and with county-level mosquito infectivity.
The effects of weather fluctuations on WNV transmission in the New York in 1999 have been analyzed by several researchers who showed that increased temperatures influence North American WNV distribution and play an important role in the maintenance and amplification of human infection. It is found positive associations with increasing temperature over each of the four weeks prior to symptom onset. Specifically, an increase of 5°C in the mean maximum weekly temperature was associated with a significant 32–50% higher incidence of reported WNF infection.
The temperature was found to be the main factor that mediates the magnitude and timing of the increased minimum infection rate within the season. Increased temperature is positively correlated with the rate of virus evolution, with mosquito abundance and infection; it influences WNV distribution and plays an important role in the maintenance and amplification of human infection.
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