Dengue in the Americas
Spanish version: Dengue en las Américas
- Case definition
- Vector
- Historical situation in America
- Risk Factors
- Surveillance, prevention and control
- References
Case definition
Clinical description.
Acute febrile illness with that lasts 2-7 days with two or more of the following manifestations: headache, retro-orbital pain, myalgia, arthralgia, rash, hemorrhagic manifestations and leukopenia.
Laboratory criteria for diagnosis.
One or more of the following:
- Isolation of the dengue virus from serum, plasma, leukocytes, or autopsy samples.
- Fourfold or greater increase in reciprocal antibody titers IgG or IgM against one or more dengue virus antigens in paired serum samples.
- Detection of dengue virus antigen in autopsy tissue by immunohistochemistry or immunofluorescence, or in serum samples by EIA,
- Detection of viral genomic sequences in autopsy tissue, serum or samples of cerebrospinal fluid by polymerase chain reaction (PCR).
Case classification.
1) Suspected: A case compatible with the clinical description.
2) Probable: A case compatible with the clinical description with one or more of the following characteristics:
- Supportive serology ( antibody reciprocal titers by hemagglutination inhibition> = 1,280, comparable titer of IgG by EIA or test of antibodies IgM positive in a serum late specimen of the acute phase or convalescent).
- Appearance in the same place at the same time of other confirmed cases of dengue.
- Confirmed: A case compatible with the clinical description that is laboratory confirmed.
Criteria for dengue hemorrhagic fever and dengue shock syndrome:
Hemorrhagic dengue.
Probable or confirmed case of dengue and hemorrhagic tendencies with one or more of the following manifestations:
- Positive tourniquet test.
- Petechiae, ecchymosis or purple.
- Hemorrhage in Mucoses, gastrointestinal tract, injection sites or others.
- Hematemesis or melena.
And thrombocytopenia (100,000 cells per mm3 or less) and signs of loss of plasma due to increased vascular permeability, with one or more of the following events:
- Increase in hematocrit index for age and sex> = 20%.
- Decrease of 20% or more in hematocrit index after the losses replacement treatment compared to the base level.
- Signs of plasma loss (pleural effusion, ascites hypoproteinemia).
Dengue shock syndrome.
All the above criteria for hemorrhagic dengue, and signs of circulatory failure with the following statements:
- Rapid and weak pulse and a decrease in pulse pressure (<= 20 mm Hg) or
- Hypotension for age, cold and clammy skin, restlessness.
Vector
The dengue virus belongs to the Flaviviridae family, having four serotypes (1-4). The infection in humans by one serotype produces only temporary and partial protection against other serotypes. All serotypes have been isolated from autochthonous cases in the Americas; however, during the period 1978-1991 only were circulated dengue serotypes 1, 2 and 4; dengue 3 was isolated in 1977 in Colombia and Puerto Rico. The dengue-1 and 4 were the serotypes that circulated predominantly during the 1980s The introduction of dengue-4 in 1981 in the Americas was followed by epidemics in the Caribbean, Central America, Mexico and northern South America in the two successive years, being asociated with the syndrome in Mexico (1984), Puerto Rico (1986) and El Salvador (1987). Dengue-4 is now endemic in the region.
Molecular studies on the nucleotide sequences of the dengue virus genomes allow the classification of the agent in genotypes. In America circulates a genotypic group of dengue-1 and two of the dengue-2 virus.
In the Americas, the persistence of dengue virus is associated with a transmission cycle human – Aedes aegypti – human. After feeding on infective blood, the mosquito can transmit the agent for a period of 8-12 days of extrinsic incubation. Transmission can also occur when the feeding is interrupted and immediately the mosquito bites a susceptible host. Aedes albopictus is the maintenance vector of dengue in Asia.
The Aedes aegypti, a specie of the Stegomyia subgenus originated in Africa and may have come to America in the water barrels transported by ships of the settlers and explorers. Their habitat is in the tropics, in a band between 35 o N and S latitude, usually at altitudes below 1000 m. In the summer can reach 45 o but they do not survive the winter in these latitudes. The female needs to feed on human blood or pets for reproduction.
Often this mosquito is located less than 100 m of housing, therefore is considered an urban mosquito, but occasionally rural infestations can occur. The eggs are disposed in the interior wet area of the containers on the water surface, completing its embryonic development within 48 hours. However the eggs can resist dry periods. The interval between the blood suction and the disposition of eggs can be as short as 3 days.
Mosquitoes use dark and quiet places for resting. Thereby, they select walls, furniture and hanging objects, such as clothing, towels and drapes. Many of the resting places are difficult to access such as the room closet, under the beds and furniture. In the house it is found in the rooms, bathrooms and kitchens. Occasionally it is found in the vegetation outside the house. Its lifetime in nature does not normally exceed much more than a week.
Historical situation in America
A Dengue-like disease has been reported in the Americas for over 200 years. The antecedent of dengue in America was linked to a outbreak ocurred in Philadelphia, USA, in 1780. In the nineteenth century four large epidemics affected the Caribbean and Southern United States. Brazil also suffered two epidemics in the nineteenth and two of the in the twentieth century. In Peru the entity was reported in the 50s. In the first half of the twentieth century were reported in the Caribbean and southern US four new epidemics. Most dengue outbreaks occurred at intervals of one or more decades until the 1960s, but thereafter the intervals have become increasingly shorter.
Dengue was first described at the global level, in northern Australia the end of last century. Although in previous centuries and half the current several epidemics and pandemics of dengue were described, since the 50s its incidence increased significantly. Hemorrhagic Dengue appeared in the Philippines in 1954 and then spread to Thailand, Vietnam, Indonesia and other Asian and Pacific countries, becoming endemic and epidemic in several of them.
The first epidemic of classic dengue in the Americas, documented by laboratory was associated with dengue-3 and affected the Caribbean Basin and Venezuela in 1963-64. Previously, only had been isolated in the region, dengue-2 in Trinidad and Tobago in 1953-54 in a non-epidemic situation. In 1968-69, another epidemic affected several Caribbean islands and during that time, were isolated dengue serotype-2 and dengue-3.
During the early and mid 1970s, Colombia was affected by extensive outbreaks associated with serotypes 2 and 3; during this period these serotypes became endemic in the Caribbean. In 1977, dengue-1 serotype reached the Americas and after its initial detection in Jamaica, it spread to most Caribbean islands causing explosive outbreaks. Similar outbreaks were observed in northern South America (Colombia, Venezuela, Guyana, Suriname and French Guiana), Central America (Belize, Honduras, El Salvador, Guatemala) and Mexico. The indigenous transmission of dengue-1 was also reported in the state of Texas, USA, during the second half of 1980. About 702,000 cases of dengue were reported by the affected countries during the period 1977-1980, in which the dengue-1 was practically the only serotype that circulated in the Americas.
During the 1980s, there was a considerable increase in the magnitude of the dengue problem in the Americas which was characterized by a marked geographical propagation of dengue activity in the region. In 1982, occurred in northern Brazil an epidemic caused by serotypes 1 and 4. In 1986, a large outbreak due to dengue-1 affected the city of Rio de Janeiro and thereafter the virus spread to several other Brazilian states. Four other countries without prior history of dengue or without record of the disease during many decades suffered large epidemics due to dengue-1, they are: Bolivia (1987), Paraguay (1988), Ecuador (1988) and Peru (1990). During the outbreak in Peru, dengue-4 was also isolated. Serologic studies suggested that several million people had been affected during these outbreaks although only were reported about 240 000 cases by the five countries during the period 1986-1990. On the other hand, there was a increase marked in the occurrence of hemorrhagic dengue fever – dengue shock syndrome.
The first reports of the syndrome corresponded to Curacao and Venezuela in the 1960s and Honduras, Jamaica and Puerto Rico in 1970. During the outbreak of the syndrome in 1981 in Cuba, associated with dengue-2, 344,203 cases were reported, of which 10,312 were severe (grade II-IV WHO) and 158 deaths, including 101 children. In October 1989, a second outbreak began in Venezuela with a total of 5,990 cases and 70 deaths. Two thirds of cases and deaths were children under 14 years. Were isolated serotypes 1, 2 and 4. Between 1981 and 1991 cases in Surinam, Mexico, Dominican Republic, Aruba, Nicaragua, Colombia, Puerto Rico, St. Lucia, Virgin Islands, Brazil, El Salvador and Honduras were reported, besides Cuba and Venezuela. Most countries had reported less than 10 cases, but Brazil, El Salvador, Colombia and Puerto Rico suffered each, more than 40 cases. Between 1981 and 1996, 25 American countries reported cases of hemorrhagic dengue and 581 deaths. while dengue-1 affected Brazil with a few cases in 1986-87, dengue-2 broke out in 1990, notifying an outbreak of the syndrome in Rio with 274 cases and 3 deaths. In 1991 dengue-2 had spread to other states in Brazil. El Salvador reported 153 cases, including 7 fatal in 1987-88 and one case in 1991. Colombia also reported 90 cases in 1991. A total of 24 countries in the Region reported the outbreak.
In 1993 Costa Rica (dengue-1) and Panama (dengue-2) reported cases of the disease, after decades of absence. In 1994 dengue-3 reappeared in the region, in Panama and Nicaragua, to spread in 1995 to other Central American countries and Mexico. In 1997 dengue-3 was remained confined to Central America and Mexico. Both in 1995 as in 1996 more than 250,000 cases of dengue were reported in the region.
Case studies of hemorrhagic dengue in the Americas revealed similarities to the clinical manifestations found in Asia, but the incidence of gastrointestinal hemorrhages observed in Cuba and Puerto Rico seem to be more elevated than that in Thai children. Hepatic necrosis afflicts 70% of the 72 children who died from hemorrhagic dengue in Cuba in 1981. There have also been reports of serious neurological manifestations, renal failure and myocarditis. The fatality rate of the hemorrhagic dengue in the Americas is 1.4%, with sensitive variability (8.3% in Puerto Rico and 0.8% in Venezuela in 1995).
Risk Factors
As risk factors, are described the simultaneous presence of the vector and the host and the conditions that favor the proliferation of transmitters mosquitoes. In 1962, 18 countries of the continental and insular region reported having eradicated the mosquito, then three other countries were added. However, later re-infestation was observed. Associated with it, were indicated little political support which resulted in a inadequate management and scarcity of trained technical personnel. It was also noted the resistance of A. aegypti to chlorinated insecticides and the campaign costs in materials, equipment and wages. In 1997, all American countries except Canada, Chile and Bermuda were infected with the mosquito. The Vector densities increase with the practices of storing water in homes due to the recurring problems of water supply and also by the increasing number of containers than can hold water, such as tires and disposable containers. Among the factors which contribute to the appearance and reoccurrence of dengue and hemorrhagic dengue can be mentioned the rapid growth and urban development of populations in Latin America and the Caribbean and the increasing mobility of people. In short, the causes that contribute to the spread of dengue and hemorrhagic dengue are population growth, urbanization and poor environmental sanitation. At present, the four serotypes of dengue circulate, increasing the risk of hemorrhagic dengue in the region.
The description of the risk factors has been particularized in macro determinants of transmission (among them the geographical area, climate and altitude, also the population density, urban unplanned development and high housing density, unprotected houses in their vain, susceptible to vector penetration, also obstruction of rainwater hoppers with ashes, and water stored for more than a week without cover, inappropriate systems for management and disposal of garbage and the presence of scrap metal, abandoned tires and small containers) and micro determinants (such as the characteristic of the hosts -Sex, age, immune status, health status, occupation-, the factors of the agent, -the viremia level -, the factors of the vector, – density of of adult females mosquitoes, age, feeding frequency, preference and availability of hosts, innate susceptibility to infection-).
Surveillance, prevention and control
Dengue, including hemorrhagic dengue, and Dengue Shock Syndrome (DSS), is the most important arthropod-borne viral disease worldwide. Is presented in more than 100 countries and territories and constitutes a threat to the health of more than 2500 million people in tropical and subtropical regions. Dengue fever is a severe disease with high epidemic potential. About 500,000 patients are hospitalized with hemorrhagic dengue o DSS every year; 90% are under 15 years of age.
Therefore are posed surveillance measures, which should be directed to:
Areas where has not been detected dengue transmission but there is Aedes aegypti: surveillance of suspected cases, with investigation of clusters of suspected cases of dengue.
Countries where the disease is endemic, with seasonal increases in transmission, and areas where dengue epidemics occur: Weekly/Monthly routine notification of aggregated data of suspected cases, probable and confirmed cases of the peripheral team to intermediate and central level.
Recommended minimum data.
Data from cases in the peripheral scope:
- Case classification (suspected/probable/confirmed), serotype, presence of hemorrhagic dengue/ DSS (Yes / No).
- Unique identifier, patient name, age, sex, geographic information.
- Date when it appeared.
- Hospitalized (Yes/No).
- Result.
- Travel made during the two preceding weeks.
Aggregated data that must be reported:
- Number of cases by age group.
- Number of confirmed cases (and serotype).
- Number of cases of hemorrhagic dengue/DSS by age group.
- Number of hospitalizations and deaths.
Principal use of data for decision-making:
- Targeting interventions to high-risk areas.
- Monitor changes in serotype and rate of hemorrhagic dengue/DSS.
- Monitor trends in the endemic disease or rate of hemorrhagic dengue: DSS.
Because of currently there is not a vaccine, vector control is the only method available to confront the decease. However, the high cost of campaigns, the need for a commitment and a performance at the continental level, the difficulties in establishing a vertical program and other difficulties prevent the necessary coordination. The Pan American Health Organization has proposed guidelines for the control and prevention of dengue and hemorrhagic dengue. These are:
- Epidemiological surveillance (Active, with laboratory support).
- Education of the medical community so it can recognize and appropriately treat cases of dengue/hemorrhagic dengue.
- Entomological surveillance.
- Vector control with emphasis on source reduction utilizing environmental management (improvement of water supply, proper solid waste management, naturalistic methods), chemical methods and biological control.
- Community participation with efforts addressed to the elimination or proper handling of potential breeding sites, physical protection of water storage areas and cleansing campaigns.
- Emergency plans to deal with dengue/hemorrhagic dengue epidemics.
Today are indicated the need for programs of well-organized and efficient control. Emergency measures to combat epidemics have had a limited effect. It is recommended to emphasize the focus on coordinated prevention and control programs.
References
Organización Panamericana de la Salud: Definiciones de Casos. Dengue. Boletín Epidemiológico, 2000, 21(2):14-15
Pan American Health Organization: Dengue and Dengue Hemorrhagic Fever in the Americas: Guidelines for Prevention and Control. Scientific Publication No. 548, Washington, 1994, 98 pp.
Organización Panamericana de la Salud: El dengue y la fiebre hemorrágica de dengue en las Americas: una visión general del problema. Boletín Epidemiológico, 1992, 13(1):9 -10
Organización Panamericana de la Salud: Resurgimiento del dengue en las Américas. Boletín Epidemiológico, 1997, 18(2): 1 – 6
Organización Panamericana de la Salud: Dengue y fiebre hemorrágica del dengue, 1996. Boletín Epidemiológico, 1996, 17(4):12-14
Organización Panamericana de la Salud: Dengue en Costa Rica y Panamá. Boletín Epidemiológico, 1994, 15(2): 9 -10
Organización Panamericana de la Salud: La Salud en las Américas. Volumen 1. Publicacion Cientifica No 569, Washington, 1998.
