Dr. Jessie Fantone said Japanese encephalitis is a seasonal ailment that usually occurs in the summer and fall in the temperate regions of China, Japan and Korea.
Expressing concern about the seven cases, Fantone said, "The occurrence of Japanese encephalitis in our country could be worse than we think."
"It is not known to be common in our country so there have been cases when doctors often make the mistake of classifying it as tubercular meningitis," he said.
He said this was what happened to the seven Tarlac residents who, however, did not respond to medications.
Meanwhile, Angeles City Mayor Carmelo Lazatin appealed to residents to rid their surroundings of possible breeding grounds of mosquitoes following a surge in dengue fever cases in the city.
Lazatin, however, downplayed reports that as many as 500 city residents have been infected by dengue in recent weeks. Dr. Rolando Esguerra, city health officer, said only 174 people have been stricken with the viral disease since January last year. Seven of them died.
Fantone said the seven Japanese encephalitis patients in Tarlac were discovered after a Japanese researcher got interested in their cases and sent their blood samples to a private hospital in Quezon City which, in turn, confirmed that they were infected by the Japanese encephalitis virus.
"The problem is that testing could cost about P1,000 which is often not affordable to people in rural areas who are most prone to the ailment," he said.
According to medical books, Japanese encephalitis can affect the central nervous system and cause severe complications and even death, and that it has no specific treatment although a vaccine is available in the United States.
Fantone said the Japanese encephalitis virus is normally transmitted by Culex mosquitoes (scientifically known as culex tritaeniorhynchus).
The virus, however, can also be carried and passed on to humans by Anopheles mosquitoes, more known as vectors of malaria, and even Aedes Egypti mosquitoes, which are carriers of the dengue fever virus.
"What’s worrisome about Japanese encephalitis is that it is often carried by Culex mosquitoes which thrive in rice paddies," Fantone said.
On the other hand, mosquitoes which transmit the dengue and malaria viruses thrive and breed in more limited areas.
Fantone, however, allayed fears on Japanese encephalitis, saying that 80 percent of its victims get well after showing symptoms. The rest suffer from some form of mental retardation, he added.
He said mosquitoes carrying the virus also prey on pigs and birds. "The infected animals do not get sick, but they serve as reservoir for the virus which mosquitoes can ingest from them and possibly transmit to humans," he said.