Assignment 11: Key Determinants

Problem Definition: There has been an increasing incidence of both classic dengue and dengue hemorrhagic fever among the adult population in Venezuela during the last two decades.


Key Determinants:


Biological:

• Individual Factors: Age, Gender, Genetic Background and Underlying Diseases: 

The host’s immune response, determined by individual factors like age, gender, genetic background and underlying diseases, plays a role in the clinical expression of DF/DHF. In Venezuela the incidence of DF has been the highest among 10 to 14 year old children, peaking in 2007 (570/100,000) On the other side, DHF highest incidence rates were observed among infants, peaking again in 2007 (62.9/100,000).

• Introduction of New and More Complex Secondary Vectors:

The number of countries with more than one viral stereotype circulating has steadily increased, favoring the occurrence of more cases of secondary infection and consequently and increase in the risk of DHF. Also, a potential additional risk is the introduction in the region of Ae. albopictus, an efficient dengue vector in Southeast Asia. Unlike Ae. aegypti, Ae. albopictus is not obligatorily anthropophilic and sometimes displaces the former from its habitat. This vector has been detected in several Latin American countries (Mexico, Honduras, Guatemala, Nicaragua, Panama, Cuba, Dominican Republic, Trinidad & Tobago, Brazil, and Bolivia); but thus far its presence has not been associated unequivocally with the increase in dengue transmission.


Social and Cultural:

• Mosquito Control is Virtually Non-Existing in the Society:

Mosquito control measures are practically non-existent in the society. In regular endemic periods, people do not take primary preventions to avoid the mosquito bite in the first place, such as using mosquito nets or lighting up citronella candles at home. Emphasis over the past 25 years has been placed on ultra-low-volume space sprays of insecticide for adult mosquito control, but this has been shown to be ineffective in controlling Ae. aegypti.

• Increased in Air Tavel

The increased travel of people by jet airplane favors the movement of dengue virus between endemic areas and other areas free of disease due to people's arrival during the disease incubation period (viremic period can be long and virus can be detected in blood from two days before initial symptoms until eight days after) and subsequent risk of infection of local mosquitoes and development of epidemics. An illustration of the increased human air travel is seen in the great number of Latin American airlines that emerged in this period of time and the increasing number of flights towards tropical areas.

Environmental:

• Population Growth

In the last 20 years, the urban population in Venezuela has more than doubled, and as a consequence, the incorporation of more land for food production and the negative impact of haphazard deforestation have created the conditions for the emergence of vector-borne diseases like dengue.

• Inadequate and Unplanned Urbanization:

The constant migrations from rural to urban areas have resulted in large, crowded human populations living in urban centres in substandard housing with inadequate water, sewer and waste management systems, creating ideal conditions for increased transmission of mosquito-borne infectious diseases.

• Trash Accumulation and Poor Urban Sanitation

The main urban centers, especially the city of Caracas, lack the appropriate urban sanitation infrastructures and the accumulation of trash is growing problem. Most of the consumer goods are packaged in non-biodegradable plastic or cellophane materials, which are discarded into the environment where they collect rain-water and provide ideal larval habitats for the vector mosquito.

• Global Warming

Increasing incidence of dengue in the Region might be be related to climatic changes that favor larval habitats for the mosquito vector, like increases in the amount of rainfall, higher sea-surface temperature, and increases in weekly minimum temperature. Although the association between climatic changes and the explosion of dengue in the Americas remains controversial; in April 2007, the Intergovernmental Panel on Climate Change concluded that global warming and climate change would cause an upsurge in dengue and other tropical diseases.


Economic:

• Decreased Access to Healthcare

Complications in cases of classic dengue that lead to an increasing incidence of DHF are related to the misdiagnosis and mistreatment of the disease when the first symptoms appear. This is the most common in low socio-economic status classes that have a more limited access to healthcare.

Political:

• Deterioration of the Public Health Infrastructure

The public health infrastructure required to deal with epidemic vector- borne infectious diseases has deteriorated during the past 20 years. Limited financial and human resources, and competing priorities for those resources, have resulted in a ‘crisis mentality’ among public health officials. The emphasis has thus been on implementing emergency control measures in response to epidemics rather than on developing programmes to prevent epidemic transmission. This approach has been particularly detrimental to dengue prevention and control because surveillance in Venezuela is very poor; the passive surveillance systems relied on to detect increased transmission are dependent upon reports by local physicians, who often have a low index of suspicion and do not consider dengue in their differential diagnosis of dengue-like illness. As a result, the epidemic has often reached or passed peak transmission before it is detected and emergency control measures are implemented too late to have any impact on the course of the epidemic.


References:
Javier Torres and Julio Castro; El Impacto Económico y Sanitario del dengue en América Latina http://www.scielosp.org/pdf/csp/v23s1/04.pdf


Duane J. Gubler; Epidemic Dengue/Dengue Hemorrhagic Fever: A Global Public Health Problem in the 21st Century; http://203.90.70.117/PDS_DOCS/B0776.pdf


José Luis San Martin; The Epidemiology of Dengue in the Americas Over the Last Three Decades: A Worrisome Reality; http://new.paho.org/hq/dmdocuments/2010/Jan%202010%20AJTMH%20Dengue%20BZ%20GD%20AB%20OS%20JSL%20OB%20MGG.pdf