Dengue is an acute febrile viral disease that greatly affects the populations of tropical and subtropical countries, both in summer and after the rainy season. This disease constitutes a serious public health problem, since the climate and urban habits create favourable conditions for the development and proliferation of mosquitoes that spread it.
Dengue is transmitted by two species of mosquitoes — Aedes aegypti and Aedes albopictus — that bite only during the day, contrary to the common mosquito, Culex, which attacks at night.
The insects that transmit the disease are spawned in clean waters, proliferating in or near dwellings or water collecting containers — water tanks, cisterns, open cans, old tyres, or plant pots. Used tyre deposits, in particular, as well as bromeliads — plants that form a kind of chalice that accumulates water — usually serve as excellent breeding grounds for mosquitoes. Although the transmission of the disease is more common in cities, it can also occur in rural areas. However, it is quite rare in localities with altitudes above 1,200 metres.
First the females lay their eggs within any container that can hold water and they adhere to its walls, while remaining near the water. Even if the container dries, the eggs do not die. Therefore, it is no use to simply replace the contaminated water with different clean water. Even if you do this, the adhering eggs always become larvae after some time, giving rise to new mosquitoes.
According to the official records, dengue was reported for the first time in 1779 on the island of Java, and in 1782 in Cuba. In Brazil, there are references to this disease from 1846. The first epidemic documented clinically and in a laboratory, however, occurred in Boa Vista, Roraima, in 1981. Another large epidemic occurred in Rio de Janeiro in 1986, extending to the states of Alagoas and Ceará. A year after that, dengue spread greatly, becoming endemic in Bahia, Pernambuco, Minas Gerais and São Paulo.
There are four different types of dengue virus in the world: dengue 1, 2, 3 and 4. In Brazil, only types 1, 2 and 3 are spread. The latter was found in December 2000 and isolated in January 2001 in Rio de Janeiro.
It should be noted that people infected with dengue (regardless of the type of virus) have the same symptoms. On the other hand, there is no need to try to determine the type of virus that caused the disease: dengue is dengue, and all those infected suffer from the same symptoms. The most effective way to avoid contamination is by eliminating the transmitting insects.
In most cases, dengue causes discomfort and physical disorders, but does not endanger people’s lives. Regarding the virus’ symptoms, it has been observed that patients are affected by a high fever, headaches and an aching body, and sometimes vomiting. Three or four days after the onset of these manifestations, minor bleeding may occur in the nose and gums, as well as rashes and red spots on the skin, similar to those of measles and rubella.
Symptoms improve after five to ten days on average. In a minority of cases, however, after the fever starts to drop, a marked decrease in blood pressure is possible, which can lead to more severe form of the virus — haemorrhagic dengue fever — and death. This serious type of dengue, although quite rare, can occur even among those who get catch the virus for the first time.
Individuals generally recover with no major problems, becoming immunised against the virus type (1, 2, 3 or 4) that contaminated them. However, they can become contaminated again with other types of the dengue virus. In other words, if someone has acquired the virus type 3, the can also be infected by viruses 1, 2 or 4. Despite there being a much greater risk of the disease progressing to haemorrhagic dengue during a second or third contamination, it does not mean that the most severe form of the virus will necessarily occur.
Aedes aegypti is present in about 3,600 municipalities and, depending on the existence of other outbreaks, the mosquitoes can also spread yellow fever and malaria.
Today, about two billion people live in areas where dengue transmission can occur. These risk areas are: Central America, South America (except Chile, Paraguay and Argentina), North America (Mexico), Africa, Australia, the Caribbean (excluding Cuba and the Cayman Islands), China, Pacific Islands, India, Southeast Asia and Taiwan. The figures of the disease have been estimated at between 50 million and 100 million cases per year. In 1995 in the Americas, 250,000 cases of dengue and 7,000 cases of the more severe form of the disease were reported.
In Brazil, in the 1930s, the eradication of yellow fever also caused dengue to disappear. But the epidemic returned to the country, reaching 570,148 cases in 1998. A year later, there was a significant reduction of the epidemic, dropping to 210,000 cases. However in 2000, there was a slight elevation (to 240,000 cases) and in 2001, the disease reached the mark of 370,000 cases. The majority of patients, it is worth remembering, live in Northeast Brazil.
It is important to note that one person does not transmit dengue directly to another. What is necessary to be contaminated is: first, that the Aedes aegypti bites someone who is infected; second, the dengue virus multiplies inside the mosquito’s body; and third, the carrier insect virus bites an individual contaminating them that way.
In Brazil, the fight against dengue has been done through the following ways: a) the extermination of adult mosquitoes; b) the elimination of larval breeding; and, c) investments in environmental education. The use of insecticides through fogging has been used. This procedure does not however prevent larvae breeding grounds (the main sources), and must always be repeated to exterminate the insects that may survive. Therefore, all containers that can be filled with water — such as water tanks and cisterns — must be protected with covers or discarded, since they are excellent breeding grounds for the insects. Finally, the Ministry of Health has invested in education, enlightening the public on ways to combat dengue in the environment.
Below are some of the important measures that have been disseminated to prevent the spread of Aedes aegypti.
1. Eliminate all living plants in pots with water, replacing them with others living in pots with soil and keep water-collecting dishes dry.
2. Use water treated with chlorine (40 drops of 2.5% bleach per litre) twice a week to water plants likely to accumulate water, such as bromeliads.
3. Always unclog roof gutters so that there is no water accumulated in them.
4. Avoid leaving tyres or other vessels that hold water exposed to rain.
5. Always keep tanks, filters, barrels, and water tanks lidded.
6. Gather rubbish in sealed plastic bags or in cans with lids.
There is still no specific treatment for dengue. When uncertain about the presence of the virus, it is recommended that the patient take paracetamol-based drugs (such as Tylenol) to relieve pain and fever, and also drink plenty of water. Additional care, in turn, should be taken. Among them is not ingesting drugs containing acetylsalicylic acid (ASA, aspirin or Melhoral), since its side-effects allow the disease to worsen.
On the other hand, the use of dipyrone-based rugs (such as Novalgina and Dorflex) is forbidden, as well as any type of anti-inflammatory (such as Scaflan, Voltaren and Profenid) because they can cause bleeding in the digestive tract and skin rashes resulting from allergic reactions.
Although research in the health field is well advanced, a vaccine against dengue has not yet been obtained. In most endemic areas, it is recommended that people use long trousers, a long sleeve shirt and repellent on their skin to prevent the insects that transmit the disease coming close to them.
Recife, 29 March 2005.
Translated by Peter Leamy, September 2016.
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Source: VAINSENCHER, Semira Adler. Dengue. Pesquisa Escolar Online, Fundação Joaquim Nabuco, Recife. Disponível em: <http://basilio.fundaj.gov.br/pesquisaescolar/>. Acesso em: dia mês ano. Ex: 6 ago. 2009.