Effect Measure

Travels in chikungunya territory

I’ve just returned from a short trip to the Emiglia Romagna region of northern Italy. The area around Bologna (site of the world’s first medical school) is said by most Italians to have the second best food in all of Italy (the best is usually “Grandma’s house”). It also has chikungunya, an imported arbovirus infection whose vector is the Tiger mosquito, Aedes albopictus.

This nasty little daytime biter was first seen near Genoa (on the other side of Italy near the French border) in 1990 but was seen in the Veneto (the region next to Emiglia Romagna) in 1992, apparently on tires imported from Atlanta. Discarded tires hold little pools of water and A. albopictus lays eggs in them. It gradually spread from this focus as the eggs traveled within Italy via human trade and transport. By 1998 the vector had spread to 22 provinces in 9 regions as far away as Rome. Among the villages where albopictus took up residence were Castiglione di Cervia and Castiglione di Ravenna in Emiglia Romagna, twin hamlets separated by a slow moving or stagnant river. Houses are low to the ground and surrounded by small gardens, including plants, flowers and flower pots, all places where water can pool and be repositories for vector eggs.

The first known (index) case of chikungunya had its onset in resident of Emiglia Romagna on June 15, 2007. He had recently traveled to an endemic region for chikungunya (Kerala State in India) and had two episodes of fever, during the second of which he visited his cousin in Castiglione di Cervia. The visit was only for several hours but apparently was sufficient for a mosquito to bite first him and then his cousin, who fell ill on July 4. Thereafter there were additional waves of disease throughout the two villages and some outsiders who were visiting family and friends. But by the end of August new cases were appearing in the region of Emiglia Romagna among people with no travel to the villages or contact with villagers. A recent status update to WHO under the new International Health Regulations have reported 131 cases, although more are expected. Older people are over represented in the cases (median age 59). It isn’t known whether this age distribution is a result of an older population in the two rural villages, more exposure of older people, more serious disease an therefore more complete reporting or some other factor. The most common symptom was severe joint pain. One elderly patient died and another remains in a coma.

So along with the first medical school, the region can now boast of the first documented chikungunya outbreak in Europe. Imported in the blood of a traveler, the virus took root in the local mosquito population (itself imported on the wings of globalization) and now has formed a small endemic focus on the European continent. The virus is known to propagate transovarially (i.e., be passed to the next generation via the eggs) in mosquitoes in the tropics, so it is likely that infected A. albopictus mosquitoes will reappear in Emiglia Romagna in the spring.

Could chikungunya become endemic in the souttheastern US where there are A. albopictus vectors? CDC doesn’t think it very likely, but before the Emiglia Romagna outbreak most people thought it couldn’t become endemic in Europe, either.

Meanwhile, chikungunya has an incubation period of about a week. The weather was pretty cool when I was there over the weekend and I wasn’t bitten by any mosquitoes as far as I know. If the blog goes dark next weekend, you can send fruit or flowers via an email attachment. I’ll eat it when I recover.

On second thought, send money instead. I find it more therapeutic.

Comments

  1. #1 gaudeamus
    November 1, 2007

    How long must an organism remain in a local environment in order to be considered endemic? There have been a few hundred cases of malaria in Jamaica recently, although malaria isn’t considered to be endemic there. Is this just semantics or is there more to it?

    Thanks for another interesting post.

  2. #2 revere
    November 1, 2007

    gaudeamus: There is no set length of time, but the idea is that the organism has “taken up residence there,” not continually imported. Also if it is at an extremely low level, then we usually don’t consider it endemic. There is also no set definition for “epidemic,” which is an large increase over the expected, but still pretty subjective. It doesn’t must mean “widespread.” It pertains to rate of change. Endemic means the rate of change is small. Other than that, it is in the eye of the beholder, although for most diseases there is general agreement on whether something is endemic, at least after enough time has passed to be confident it is genuinely residing in a locality.

  3. #3 tan06
    November 2, 2007

    Aedes albopictus containing chikungunya is also sent from tropical regions to nations with a more modest climate in a lovely wired sort of dwarf bamboo, which can be purchased in flower shops.
    Checking samples of these plants revealed the Tiger mosquito and the disease in The Netherlands. So when you’re getting ill, please check the ‘lucky greeting’ I’ve sent you for your birthday, Revere.