North County Grapples With a Biting Problem--Malaria : Cases Nearing Major Outbreak of ’52

You don’t need a steaming jungle to have a malaria outbreak, as San Diego County is learning with a spate of cases that is threatening to become the largest U.S. outbreak of the disease since 1952.

The number of malaria cases in the Lake Hodges area of North County rose to 23 Monday with the addition of two more migrant farm workers to the list. A third worker, who has not yet been located, probably also has the disease, said Dr. Donald Ramras, the county’s chief public health officer.

That puts the county close to the total of 27 in 1986 in Carlsbad, which Ramras wouldn’t be surprised to see surpassed.

“We think we’re going to have more cases,” he said. “If I had to guess, I would say, yes, I think we’ll have as much or more than we had two years ago.”

35 Cases in 1952

The largest post-World War II outbreak in the country occurred in 1952, when 35 Camp Fire Girls contracted the disease from mosquitoes in Nevada County, said Dr. Ronald Roberto, chief of the disease control section of the State Department of Health Services. The 1986 outbreak here was second to that in size.

The current San Diego outbreak is the 13th time since 1952 that California--which accounts for about one-third of the U.S. malaria cases every year--has recorded anyone contracting the disease from mosquitoes in the state, Roberto said. More commonly, isolated malaria cases occur in recent immigrants or people who have traveled to the tropics.

Symptoms include high fever, headaches and chills, which often occur every two to three days interspersed with periods of feeling fine.

Although the first case in the current outbreak probably came to the United States in a resident of Mexico or Central America, where the disease is more common, it has been incubated and spread strictly within U.S. borders, county officials say.

With roughly two weeks between each stage of the infection process, the parasite that causes the disease, Plasmodium vivax, travels from an infected person to the Anopheles mosquito, then to another person. If that person is bitten at the right time by an uninfected mosquito, the cycle begins again.

Conditions Appear Right

“For you to have transmission you have to have the right mosquito that’s going to bite someone that’s infected at the right state of their (infection) cycle,” said Dr. Sharon Reed, an infectious-diseases specialist at UC San Diego Medical School.

“So usually what happens is there aren’t enough mosquitoes around to cause a problem, or there aren’t enough infected people,” she said.

In this case, the Lake Hodges area has been providing both. The insects breed in water around the lake, and the area also has a number of migrant farm workers camping out, available targets for a mosquito.

Although malaria is seen as a tropical disease, it can occur in any area where mosquitoes live. For instance, the Camp Fire Girls’ malaria in 1952 came to this country from chilly Korea, in a war veteran, Roberto said.

Not every one of the dozen or so mosquito types in Southern California can transmit disease, but rapid urbanization is increasing the populations of the few types that can, said Mir Mulla, an entomologist and mosquito specialist at University of California, Riverside.

Waste water outlets, which increase as the population grows, are favorite breeding spots for Anopheles mosquitoes as well as for other urban mosquitoes that can transmit encephalitis, he said.

Pools a Problem, Too

That quintessential Southern California accessory--the swimming pool--is another culprit.

“Those mosquitoes can breed in gutters, catch basins, storm drains, flood control channels and even swimming pools,” Mulla said. “When swimming pools are not attended, they can produce a tremendous number of mosquitoes in just a week or so.”

In a single week, one unattended pool

can produce millions of mosquitoes and infest a 10- to 20-block area, he said.

Through July 23, California had 138 cases of malaria this year, all but one of them acquired outside the state. There have been 423 cases nationwide.

“The reason is that we get a lot of immigrants from Asia, and from Central America and Mexico,” Roberto said.

Monday, county health workers were searching through migrant camp areas around Lake Hodges to find other people who might have the disease and to give preventive drugs to those who don’t have it, Ramras said. The preventive drugs must be taken weekly for several weeks. If the disease has already been contracted, a two-week regimen of medication cures the strain that is being seen here.

Other workers were spraying oil on waters where mosquito larvae live during the day and fogging mosquito-infested areas at night. Traps show that the measures taken over the past several days already have reduced the numbers of mosquitoes in the Del Dios residential area where at least one person has contracted malaria, said Moise Mizrahi, chief of the vector control division for the county.

Last Tuesday, a physician reported the first case of malaria in the outbreak, and the total had risen by the weekend to 21.

County health officials advise against outside activities at night in the Lake Hodges area, but they say other areas of the county are unlikely to have malaria-infected mosquitoes.