Report says chikungunya could return in Europe next spring

Nov 6, 2007 (CIDRAP News) – Health experts who investigated Europe's first chikungunya outbreak involving transmission by local mosquitoes recently reported that cases could occur again next spring unless vigorous mosquito surveillance and eradication measures are used to control the disease in Italyand prevent its spread to other parts of Europe.

In late August, Italy's health ministry confirmed an outbreak of chikungunya in the Emilia-Romagna region of northeastern Italy.About a week later, health authorities said the outbreak represented the disease's first foothold in Europe, according to Sep 6 report in EurosurveillanceWeekly.

Soon afterward, experts from the European Centre for Disease Prevention and Control (ECDC) and the World Health Organization (WHO) traveled to Italy to assess the risk of chikungunya to the local population and the potential for its spread to other European countries. In late October the investigators posted their findings on the ECDC's Web site.

Chikungunya, spread by Aedes albopictus mosquitoes, usually causes fever, headache, fatigue, nausea, vomiting, muscle and joint pain, and a rash, according to the US Centers for Disease Control and Prevention (CDC). The disease is not life-threatening, but fatigue or joint pain can last for weeks to months. There is no vaccine or specific antiviral treatment for the illness, which is caused by an Alphavirus.

The United States has recorded some chikungunya cases among returning travelers but has not reported any transmission of the disease.Though two mosquito species that can spread the disease are found in the southeastern United States, CDC expert Dr. Ned Hayes has said the risk of indigenous transmission is probably low because lifestyle factors such as air conditioning and window screens protect people from heavy exposure to the mosquitoes.

As of Sep 21, Italian authorities had reported 292 suspected cases of chikungunya, of which 125 had been confirmed, according to the ECDC-WHO report. The outbreak started in late June when a local resident who had traveled to India fell ill with the disease. Soon afterward, the virus was believed to have spread among local A albopictus mosquitoes.

The outbreak was largely contained to two neighboring villages where the man and his cousin lived, but authorities reported that transmission through infected mosquitoes has occurred in at least three other towns.

Four factors helped the virus become established in Emilia-Romagna region, the investigators found:

  • A albopictus populations were dense in the region, but surveillance had not yet noted their presence because it was so recent.
  • Local vegetation was thick and many backyards had plant pots and watering containers that harbored mosquitoes.
  • The virus was introduced by a visitor returning from an area where chikungunya is endemic.
  • Human population density was sufficient for disease transmission.

Investigators said mosquito activity was expected to continue through October but could extend into November, depending on weather conditions.

Infected mosquitoes could reappear in the spring of 2008 when mosquito eggs hatch, the authors reported. Further, if the region has a mild winter, local mosquito activity could persist, causing sporadic cases that could maintain mosquito-to-human transmission cycles until spring, they added.

Careful surveillance and rapid mosquito-control measures will be the keys to preventing or limiting a recurrence of the disease in 2008, the report says. It notes data gaps on A albopictus populations in some areas of Europe where the vector could reside. A albopictus is found in several other European countries, including Albania, France, Belgium, Montenegro, Switzerland, Greece, Spain, Croatia, the Netherlands, Slovenia, Bosnia, Herzegovina, and possibly more, according to the Eurosurveillance Weekly report.

"The current epidemic is a unique opportunity for better understanding of risk factors and virus and vector dynamics, in order to allow for a correct preparedness on the European level to prevent or limit future outbreaks," the report states.

The investigators wrote that a better understanding of the climate, humidity, and light needed to support A albopictus populations is needed to help predict the geographic spread of chikungunya.

See also:

Sep 6 Eurosurveillance report

Sep 10 CIDRAP News story "Chikungunya fever gains foothold in Europe"

CDC information on chikungunya

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