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At least 28 people in Darien and the eastern part of Panama province have come down with some strain of equine encephalitis since the beginning of June. One of these, a two-year-old girl, has died. Most of the identified cases have been mild, but 11 people have been hospitalized. Among horses there have been at least 69 cases identified, at least 45 of which have died. The outbreak began in the Darien near the Colombian border, with cases among people or horses moving across the Gulf of San Miguel estuary into rather remote parts of Yaviza and Meteti districts, then into eastern Panama province's Chepo district and now the Panama City corregimientos of 24 de Diciembre, Alcalde Diaz and Chilibre. On June 19 a national health alert was declared.

In humans there are three known varieties of equine encephalitis: Eastern, Western and Venezuelan, all of which include Panama in their ranges. This is a viral disease, caused by variants of the Togaviridae family and Alphavirus genus, close cousins of the virus that causes the West Nile disease. The unaffected equine encephalitis reservoirs are birds and it is believed some forest rodents. Mosquitoes, mostly but not exclusively of the Culex genus, serve as the vectors that spread the disease to horses, donkeys and human beings. People and horses are "dead end reservoirs" in that mosquitoes rarely find enough viruses in an infected person or horse --- even a gravely ill one --- to further spread the disease. The virus can infect cattle, swine or dogs, but these animals do not get sick and apparently do not serve as viable reservoirs for its further spread. There is no known vaccine or treatment for the disease in humans, but for horses there is a vaccine that's effective against both the Venezuelan and Eastern forms of the disease.

If a human comes down with equine encephalitis, there are flu-like symptoms which may be aggravated by neurological symptoms and seizures that can result in death.

The disease in question here has been variously identified in epidemiologists' Internet discussion groups and by public health officials talking with news media as Eastern equine encephalitis and Venezuelan equine encephalitis, both of which Panama has seen before. But the norm in the Eastern form of the disease is a high human mortality, between one-third and two-thirds, which we have not seen. The Venezuelan form of the disease, however, does not normally take nearly such a high human death toll. Most horses that get either disease die. The Gorgas Memorial Laboratory is working to identify the virus but if they have come to a definite conclusion they have not shared it with the Panamanian people --- which is the norm for that public institution.

What we are seeing in the symptoms and the mortality among humans and animals, and the slow identification process, suggests that it might be an emerging new strain. Worldwide, public health officials are concerned that changing climate, evolving human lifestyles and people moving into previously wild areas are contributing to the emergence of new diseases or the reappearance of old ones that had not been seen in awhile.

The Martinelli administration's response to the outbreak has taken two main avenues of attack and several smaller ones. First, it obtained a supply of 20,000 doses of the horse vaccine from the Mexican government, and it's urging all horse owners to vaccinate their animals immediately. Second, wherever a case has been reported in a human or a horse, the Ministry of Health is sending in fumigation crews to spray for mosquitoes. People are also being advised to improve their sanitary practices, spread lime on outdoor privies, and promptly report any illness in a horse. Also, anyone with severe flu-like symptoms should get medical attention because it may be something substantially more dangerous than a garden variety flu strain.