It is called "one of the great neglected diseases of mankind," because it has been present in the tropics for hundreds of years and yet so little is known about it.

It is now attacking Cuba, where Fidel Castro -- in a statement that makes no medical sense -- has said it "could have been introduced" by the "Yankee" CIA.

It could appear in equally virulent form in much of the rest of the Caribbean in "weeks or even days," public health experts fear, and could spread to Central America and up through Mexico to Texas. The Brownsville, Tex., area could be vulnerable because of an earlier outbreak there.

"It would be a miracle" if it does not soon spread in the Caribbean, one of the world's leading authorities on the disease, Dr. Scott B. Halstead, warned in an interview last week.

The disease is called "dengue fever." Or just "dengue" (pronounced "DEN-gy"). Or "breakbone fever" for the aches and malaise that is causes.

Or, when it strikes in its most dangerous, sometimes fatal form as it is doing in Cuba, it is known as "dengue hemorrhagic fever" or "dengue shock syndrome." According to the latest report, there are more than 200,000 cases of this form of dengue, which has caused 113 deaths in Cuba.

Authorities in Florida announced yesterday that five Haitian refugees in a refugee camp had contracted dengue fever but said there was no danger of its spreading because the mosquito that carries it is not present.

Cuba upset some Americans and international health officials because it waited until mid-July before asking the Pan American Health Organization -- the Americas' branch of the World Health Organization -- to buy 300 metric tons of the pesticide, Abate, to spray and eradicate the aedes aegypti mosquito. This "yellow fever mosquito" also spreads dengue viruses.

PAHO officials on July 17 asked the State Department to issue a special export license, and "we issued it the same day," said Timothy Brown, State Department Cuban desk officer. But the pesticide will not be shipped until this week, at earliest.

"It takes a long time to get 300 tons together," a PAHO official said.

It is "urgent" now that health officials throughout the Caribbean and nearby areas of Central and Latin America -- and also Florida, "where there is so much contact with the Caribbean -- take several precautionary steps, said Dr. Halstead. The chief of tropical medicine at the University of Hawaii, he is author of one of the main theories on the way dengue hemorrhagic fever spreads.

The most essential steps, he said, are aedes mosquito control and training programs for medical workers and the public in recognizing and rapidly treating the hemorrhagic disease.

PAHO is doing a good job, he said, in disseminating the essential facts in potentially affected countries. Dr. Steven Waterman of the U.S. Centers for Disease Control said "we're keeping a close watch" but mosquito control seems in order and "we see no emergency" in this country.

There are four distinct dengue viruses -- or "types" of dengue virus. It is apparently Type 2 that is doing the main damage in Cuba.

The Cuban Type 2 may simply be an extra virulent type.

Or, Halstead believes, Cuba may be seeing a phenomenon he believes he has discovered. A hemorrhagic outbreak, he thinks, hits only a populace that has been infected perhaps one to four years earlier, with a milder virus, like the Type 1 that hit much of the Caribbean starting in 1977 and 1978.

If this is true, it means several Caribbean countries -- as well as some Latin American nations, including Mexico -- could be ripe for a serious Type 2 invasion. So could Brownsville, Tex.

Whether or not Halstead is correct, medical authorities believe Castro is confronting no newly imported "Yankee" disease in Cuba, but one that has been "endemic" or common in various forms for a long while.

The brownsville area is the only part of the United States that has seen dengue fever, other than scattered cases imported by travelers, such as the five Haitians. So Halstead does not fear a Cuban situation elsewhere in this country.

When the hemorrhagic form strikes, he says, it is most dangerous in children. It often goes unrecognized at first, and "doctors and parents must know" that if a sick child suddenly becomes cold and clammy and weak, or collapses, "there may be only a few hours before a possibly fatal outcome."

There is no specific drug, but doctors can often stave off the worst with fluids and other hospital treatment.

Though some dengue is present throughout the Caribbean all the time, the only new situation reported other than Cuba's is a "mild" dengue Type 4 outbreak in Dominica in the Leeward Islands.

Should travelers shun the Caribbean? Not by present indications but they should avoid mosquitoes if possible, Dr. Waterman said. The "mild," non-fatal form of the disease may closely resemble a case of flu, and often makes victims sick for four or five days or longer.