Dengue at Pandemic Levels

Dengue fever and dengue hemorrhagic fever (DHF) are viral diseases transmitted by Aedes mosquitoes, usually Aedes aegypti. The four dengue viruses (DEN-1 through DEN-4) are immunologically related, but do not provide cross-protective immunity against each other.

Dengue, a disease found in most tropical and subtropical areas of the world, has become the most common arboviral disease of humans. More than 2.5 billion persons now live in areas where dengue infections can be locally acquired. Epidemics caused by all four virus serotypes have become progressively more frequent and larger in the past 25 years. As of 2005, dengue fever is endemic in most tropical countries of the South Pacific, Asia, the Caribbean, the Americas, and Africa. Here are some of the latest reports:

Viet Nam: Heavy rains have again hit northern Viet Nam following the worst floods to hit the region in over 35 years. Authorities in the capital say they are trying to contain the spread of dengue fever after 180 cases of the mosquito-borne disease were reported by Hanoi hospitals in a 6 day period. The number of dengue cases is likely to rise as people store drinking water, thus providing more breeding sites for the dengue virus vector mosquito, Aedes aegypti.

Pakistan: Within 48 hours, 154 fresh cases of dengue fever were confirmed in the government hospitals in Punjab on 6 Nov 2008. The Punjab Health Department said that the number of dengue patients has soared to 437.

South Pacific: Samoa, Tonga, Kiribati, New Caledonia, and Palau have reported high levels of dengue fever. In Fiji, there are about 2000 people infected from a population of just over 900 000. It is probable that a new dengue virus serotype is circulating in these areas and that existing immunity from previous infections by other dengue virus serotypes is not protective.

Mexico: There have been 32 confirmed cases of classical dengue fever in Parque Hundido and surrounding neighborhoods of the Gomez Palacio municipality of Durango. The Parque Hundido neighborhood continues to be the area most affected by dengue, not only in the Gomez Palacio area, but in the whole of the Comarca Lagunera. Comarca Lagunera is the large metropolitan area located on the border between the states of Coahuila and Durango that includes 15 municipalities.

Authorities are emphasizing the need for standard precautions - eliminating all possible water catchments, such as buckets, tubs, flower vases, and bottles; cleaning up patios; putting mosquito larvicide in water-based heat pump systems; opening windows when fumigation machines pass by; and using insect repellants and
insecticides in the house.

Dengue fever is characterized by sudden onset after an incubation period of 3-14 days (most commonly 4-7 days) of high fevers, severe frontal headache, and joint and muscle pain. Many patients have nausea, vomiting, and a maculopapular rash, which appears 3-5 days after onset of fever and can spread from the torso to the arms, legs, and face. The disease is usually self-limited, although convalescence can be prolonged. Most patients report a nonspecific viral syndrome or a flu-like illness. Asymptomatic infections are also common. Although these patients do not experience symptoms at the time of the acute infection, the immunity that results increases the risk for DHF during a subsequent infection. Approximately 1% of patients with dengue infection progress to DHF. As the patient’s fever resolves, usually 3-5 days following the onset of fever, patients may develop leaky capillaries, which allow serum proteins and fluid to accumulate in the pleural and abdominal cavities. Thrombocytopenia and hemorrhagic manifestations, which can range from microscopic hematuria or increased menstrual flow to hemetemesis, are part of the syndrome. Neutropenia, elevated liver enzymes, and disseminated intravascular coagulation are also common. The case-fatality ratio for DHF averages about 5% worldwide, but can be kept below 1% with proper clinical management. Dengue shock syndrome is the progression of DHF to a hypotensive state. Despite the name, the progression of DHF to DSS is primarily due to capillary leakage rather the hemorrhaging.