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Mosquito population spikes, virus warning issuedCulex tritaeniorhynchus, vector for Japanese encephalitis virus, population increases
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승인 2014.08.13  11:46:09
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▲ The Culex tritaeniorhynchus Photo Courtesy Korea Centers for Disease Control and Prevention

With the increase in summer heat there has also been a spike in mosquito numbers across the Korean peninsula and Jeju Island. This has led to fears of Japanese encephalitis (JE) as its vector, the Culex mosquito, has been recorded in high numbers.

Every summer the Korea Centers for Disease Control and Prevention (CDC) screens the number of mosquito species across the country to ascertain the threat posed by certain species carrying harmful viruses or parasites such as the JE virus and malaria to manage possible outbreaks.

The Culex mosquito species is known to be a vector for the JE virus and on July 28 to 29, Busan CDC reported they accounted for 53.3 percent of all mosquitoes found, slightly above the guideline figure of 50 percent.

As such, the CDC issued a nationwide “alert” alarm on Aug. 5 and authorities await the results of virus screening on the insects. The density of the Culex in 37 other screening regions, including Jeju, remains below 50 percent.

However, the Jeju Public Health and Environmental Research Institute has reported a spike in total mosquito numbers after monitoring in recent weeks and accordingly the public has been asked to be take measures against mosquito bites.

These measures include using mosquito nets and mosquito repellents, wearing long sleeves when outdoors and avoiding stagnant water where mosquitoes breed, such as rice paddies and covered riverways.

As for local efforts, Jeju sanitation authorities are operating anti-endemic sterilizations for Japanese encephalitis by targeting mosquito larva in ponds and apartment complex septic tanks and sterilizing public toilets, covered rivers, and streams.

Symptoms of JE include a high fever, headaches, abdominal pain, and sudden neurologic changes such as seizures and altered mental status including loss of consciousness. However, not all Culex mosquitoes carry the virus, and 95 percent of people infected are asymptomatic (see below).

The CDC emphasized the need for timely immunization for children aged 12 months to 12 years and recommended preventive measures during the high season until October.

So far this year there has been only one recorded case of JE and that was contracted in Laos, rather than in the country. In recent years there have been between five and 20 cases annually within Korea.

Japanese encephalitis

Sources: Harrison's Principles of Internal Medicine; Tintinalli's Emergency Medicine: A Comprehensive Study Guide.

Japanese encephalitis is a Culex tritaeniorhynchus mosquito-borne virus infection that occurs in an epidemic or sporadic pattern over large areas of rural Asia and Southeast Asia, primarily in rural rice paddy fields.

95 percent of infected persons don’t present any symptoms but could have a low-grade fever without suffering from the encephalitis which is a severe outcome.

Symptoms and signs usually arise after the incubation period of five to 15 days, and infected patients present with a sudden high fever, headache, neck stiffness, vomiting, and sudden neurologic changes such as seizures (especially in infants).

Treatment for the infection is primarily supportive and includes IV fluid and electrolyte management, assisted respiration, anticonvulsant medications, neuropsychiatric consultation during recovery period which may take months.

On the other hand, the most effective measure to prevent this infection is immunization. The vaccine for Japanese encephalitis has an efficacy rate over 90 percent and in Korea it is an essential immunization for all children over 12 months.

CDCs in other countries in Europe and America recommend immunization for JE before travelling to endemic regions if stays are planned of more than one month in rural endemic areas or for shorter periods if exposure risk is high (camping, bicycling, hiking, etc).

Additional preventive measures includes using mosquito repellents and nets during the high-risk season (from August to October), and to avoid mosquito breeding areas such as rice paddy fields.

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