-from Epidemiological Bulletin, Vol. 23 No. 1, March 2002-

Dengue in Brazil: Current Situation and Prevention and Control Activities

Background
Aedes aegypti, the principal vector of dengue in the Americas, has found modern environmental conditions very favorable for its dissemination. Among these favorable conditions are rapid urbanization that has led to deficiencies in water supply services and urban cleaning, the intensive utilization of non-biodegradable materials such as disposable plastic containers, glass and aluminum, climate changes that accompany global warming, and intensified international transit of people and products.

In 1973 it was declared that A. aegypti had been eradicated from Brazil. However, three years later, the vector reappeared and since then has gradually spread throughout the country. In the beginning of the 1980s the first cases of dengue were reported in the state of Roraima, in the northern region of the country. These reports showed circulation of serotypes 1 and 4 of the virus, however, at this time, no significant indigenous transmission was observed. Starting in 1986 the first epidemics occurred, reaching Rio de Janeiro and some capitals of the northeast. Since then, dengue has become endemic in Brazil, and is associated with epidemics that introduce new serotypes into previously unaffected areas. In the epidemic of 1986, circulation of the serotype DEN 1 was initially detected in the state of Rio de Janeiro and spread to six states by 1990. That year the circulation of a new serotype, DEN 2, was detected, also in the state of Rio de Janeiro.

During the nineties, the incidence of dengue increased greatly as a consequence of the dissemination of A. aegypti in the country, beginning mainly in 1994 (figure 1 and figure 2). Dispersion of the vector was followed by the dissemination of serotypes 1 and 2 in 20 of the 27 states of the country. Between 1990 and 2000, several epidemics occurred, principally in the major urban centers of the southeast and the northeast of Brazil, where the majority of reported cases were concentrated. The midwestern and northern regions were subsequently affected by dengue epidemics starting in the second half of the 1990s. The greatest incidence of the disease was observed in 1998, with 528,000 cases (figure 1).

Circulation of serotype 3 of the virus was detected for the first time in December 2000, also in the state of Rio de Janeiro and, subsequently, in the state of Roraima, in November 2001. The introduction of that serotype could have been due to the intense movement of people along the border region between Brazil and Venezuela, where the four serotypes of the virus circulate.

Several studies have been conducted to determine the genetic characteristics of each serotype in circulation in the country. Serotype 1 is of a Caribbean strain, serotype 2 is of a Jamaican strain and serotype 3 is of a Sri Lanka strain.

Current situation
To better understand the epidemiological situation of dengue in Brazil, it is necessary to evaluate each of the five major regions, since behavior of the disease is different in each one.

In 2002, it has been observed that the diffusion of serotype 3 from the state where it was originally detected presents a different profile from the diffusion observed with serotypes 1 and 2. Previously, diffusion of a new serotype occurred slowly and some years elapsed before indigenous cases occurred in other states. In the first three months of the current year, the presence of the new serotype of the virus has been detected in ten more states (Bahia, Ceará, Goiás, Mato Grosso, Mato Grosso do Sul, Minas Gerais, Pará, Paraíba, Pernambuco and São Paulo).

In the first months of the year, the suspected and confirmed cases of dengue increased considerably in some states, strengthening the trend toward the increase in cases observed in 2000 and 2001 (figure 1). In that period, epidemics occurred in several states of the country. The total number of cases reported from January to March in 2001 and 2002 in the regions and states of the country are presented in table 1.

In the southeast, the increase is observed mainly in the state of Rio de Janeiro, with nearly 145,000 reported cases until the epidemiological week 13. This number corresponds to 45.8% of the total recorded cases in the country (preliminary data) (table 1). The metropolitan area, where the capital city of Rio de Janeiro is situated, presents more than 60% of the cases recorded in the state. The results of monitoring the circulation of the virus reveal a predominance of serotype 3 in the current epidemic. From January to March 2002, the state of Espírito Santo presented an important increase in the number of cases in comparison with 2001, while the states of São Paulo and Minas Gerais reported a reduction in the cases recorded in that same period (table 1).

In general, the states of the northeast presented an increase in reported cases in January, in particular in Pernambuco which reported 53,000 suspected cases until week 13 (preliminary data). This number of cases could reflect the circulation of serotype 3 in that state, since it was isolated in the capital (Recife) and in other municipalities of the metropolitan area and of the interior. Bahia and Rio Grande do Norte also presented an increase in the number of reports, although the number of cases is lower than in the same period of 2001. In the state of Bahia, studies have shown a high prevalence of previous infection by serotypes 1 and 2, which indicates that the current increase of observed cases could have to do with the circulation of serotype 3.

In the midwestern region, the disease presented different epidemiological characteristics from previous years, in which the cases always increased starting in the third week of January. The number of cases in the states of Goiás and Mato Grosso do Sul began to increase starting in November 2001, nearly two months before expected, based on the seasonal behavior previously observed.

The states of the northern region, in general, presented a decrease in the number of cases reported from January 2001 to January 2002. The states of Roraima stand out, however, with indigenous circulation of dengue 3 starting in November, and a small increase of cases in January. The state of Tocantins experienced a marked increase in cases from November 2001 to January 2002 that coincide with the patterns observed in the Midwestern region.

In the southern region in January and February 2002, the state of Paraná presented a significant reduction in reported suspected cases in comparison with 2001. The states of Santa Catarina and Rio Grande do Sul remain free from indigenous transmission, although the number of imported cases has increased compared to the same period of the previous year.

The number of serious cases of the disease also presented an important increase in 2002. Health care services are reporting more frequent thrombocytopenia conditions below 100,000/mm3. The number of cases of dengue hemorrhagic fever (DHF) in the country also increased: the total number of cases confirmed until the epidemiological week 13 of 2002 was 1,559 with 60 deaths, while throughout 2001, 682 cases were recorded with 29 deaths. The number of confirmed cases and deaths by DHF are presented by state of residence in table 1.

Prevention and control
Favorable socio-environmental conditions facilitated the spread of A. aegypti, since its reintroduction in 1976. Methods traditionally used in the fight against vector-borne diseases in Brazil and in the continent have not been successful in controlling the vector. Previous programs centered on chemicals, with limited o no community participation, without intersectoral integration and with little utilization of epidemiological instruments. These programs were unable to contain the vector because of its great capacity for adaptation to an environment rapidly changing by urbanization and new customs.

In 1996, the Ministry of Health decided to revise the strategy against A. aegypti and proposed a Program of Eradication of the vector (PEAa). The new program took into account the difficulties of the previous control strategy and, paradoxically, it proposed an even more complex objective, stemming from the assumption that the vector could be eradicated. Though the PEAa stemmed from this mistaken assumption and presented omissions or deficiencies in important areas such as community participation and epidemiological surveillance, it had undeniable merits. For example, the program proposed multisectoral action and foresaw the participation of the three levels of government: federal, state, and municipal, in the endeavor.

In practice, the PEAa contributed to strengthening the fight against the vector, considerably increasing resources for the project. Prevention activities centered mainly around utilization of insecticides.

Results obtained in Brazil and at the international level, brought into question the viability of a short-term policy of eradication of the vector. This led the Ministry of Health to reevaluate the progress and limitations of the program, with the objective of establishing a new program to control dengue.

The increase in observed incidence of dengue in the last two years and the introduction of a new serotype (DEN 3), led to a prediction of increased risk of dengue epidemics and an increase of the cases of DHF. To face the expected risks for 2002, the Ministry of Health, in collaboration with the Pan American Health Organization, carried out an international seminar in June 2000 to evaluate the situation and prepare an intensified plan of dengue control activities (PIACD). The plan points out the 657 municipalities of greatest risk in the country (figure 3), with the objective of targeting action and more effectively utilizing the positive results of previously adopted initiatives. These include: 1) a large infrastructure for vector control in the states and municipalities (vehicles, spraying equipment, microscopes and computers), 2) nearly 40,000 agents trained in vector control, in more than 3,500 municipalities, and 3) a set of nationally standardized activities and technical standards for vector control.

The PIACD emphasizes the need to change the models of previous programs designed to fight dengue, basically in two essential aspects: 1) the preparation of permanent programs, since there are no technical signs that the mosquito can be eradicated in the short term, 2) information and motivation of people so that every family assumes a greater responsibility for the maintenance of a domestic environment free from possible vector breeding sites and 3) strengthening epidemiological and entomological surveillance to expand the capacity for outbreak foresight and early detection.

The fight against dengue began to intensify in Brazil in October 2001, though strengthening of the infrastructure by procurement and distribution of vehicles for transportation of teams, supervisors, and equipment (such as insecticide sprayers and entomological microscopes) in the 25 states included in the plan. Eighty-nine thousand community health workers were trained to carry-out a broad program of the Ministry of Health aimed at expanding access to basic care. These workers disseminate information regarding domestic prevention of the mosquito A. aegypti and monitor suspected cases of dengue. A new model to monitor the activities of epidemiological surveillance was developed and is being implemented in the health offices of priority municipalities and states. This strategy utilizes informatics programs and optimizes analysis of the data generated by the system. These regularly carried-out analyses increase the sensitivity and capacity of outbreak detection and provide information that facilitate decisions related to intensifying control measures.

Monitoring field activities in the struggle against the vector will intensify during the course of the year. Frequent surveillance will make it possible to detect deficiencies in activities, as environmental factors and the behavior of the population change. Deficiencies could range from the number of trained staff and supervisors to articulation of external measures in the health sector.

In several Brazilian municipalities, serotype 3 found suitable conditions for epidemics due to the high indices of infestation of the vector. A critical epidemiological situation has arisen due to insufficient quantity and quality of field equipment, an incipient or even absent mobilization of the population to enact control measures and to an early summer that began with a great deal of heat and rain since the end of the last year.

In Rio de Janeiro, the state with the greatest incidence of cases of dengue and DHF, as well as deaths from this disease, the Ministry of Health, through the National Health Foundation (FUNASA), had to intervene directly to prevent major damages. In the beginning of February, a special working group was formed at the federal level with the participation of 1,000 endemic disease control agents transferred from other states to work in the most infested areas. At the beginning of March, 1,300 soldiers from the Army and the Navy joined that group to complement the municipal agents and guarantee the full coverage of all the municipalities of the metropolitan area of Rio de Janeiro. Furthermore, measures were adopted to improve the care of patients with serious forms of the disease, such as training of physicians, expansion of the availability of beds for fast care, and improvement of the organization of the case referral system.

On March 9, a great mobilization known as “D-Day against Dengue” was carried out in Rio de Janeiro. With the support of an intense advertising campaign and of governmental and nongovernmental organizations, it was possible to mobilize nearly 715,000 volunteers and motivate families to carry out a self-inspection of their domestic environments that day. Similar initiatives have been carried out in other states, with equal success. A greater awareness of dengue has developed as well as a new perception that dengue should not be treated as a banal disease and that community participation is indispensable to control the vector.

The measures adopted in Rio de Janeiro were accompanied by a marked reduction in the number of cases (figure 4 ), outpatient consultations and hospitalizations. In other states a similar trend is being observed.

The introduction of the serotype 3 and its fast spread to eight states in only three months show the facility with which new serotypes or strains of the virus can be introduced. These facts point out the possibility that new epidemics of dengue and DHF could occur. In this epidemiological situation it is indispensable to intensify the set of activities planned and in progress, to better approach the problem and reduce the impact of dengue on Brazil.

Source: Prepared by Drs. Jarbas Barbosa da Silva Jr., João Bosco Siqueira Jr., Giovanini E. Coelho, Paulo T.R. Vilarinhos, and Fabiano G. Pimenta Jr. from the National Epidemiology Center (CENEPI) / FUNASA / Ministry of Health of Brazil.

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Epidemiological Bulletin, Vol. 23 No. 1, March 2002