Aspects such as temperature, rain and moisture influence reproduction, survival and biting rates of Aedes aegypti and Lutzomyia sp., vectors of these two diseases.
In fact the El Niño–Southern Oscillation (ENSO) phenomenon and its two extreme stages El Niño (warm) and La Niña (cold) are related to the intensification of diseases transmitted by insects.
Luz Adriana Acosta Cardona, Universidad Nacional de Colombia (UNal) in Medellín Environmental and Development M.Sc. discovered common elements in climate variation which enable correlating dengue and leishmaniasis transmitters after researching climate information between 2005 and 2014.
According to Acosta the influence of the El Niño phenomenon over dengue spreads in form of a travelling wave which starts its journey from the Colombian southwest and travels northeast. In other words the municipalities closest to the Pacific Ocean have dengue cases before the rest of the country, while the areas farther from the coast have a 9 month lag. For instance cases begin to appear in the Province of Valle del Cauca after four months of an outbreak in the Pacific.
“On calculating an average for Colombia, results evidence that the lag between the El Niño Phenomenon and dengue outbreaks is 7 months,” said Acosta.
The information on disease cases was obtained through the National Institute of Health’s National Public Health Surveillance System. Weather data was based on two ENSO indexes: The Oceanic Niño Index (ONI) and the Multivariate ENSO Index (MEI) which classifies the El Niño and La Niña phenomena according to the US National Oceanic and Atmospheric Administration (NOAA).
With the research project they hoped to research the relationship between ENSO and dengue cases in three spatial scales: in Colombia, in the main provinces in Colombia and all the municipalities of the Valle de Aburrá.
Therefore they carried out a lag correlation analysis between both figures to obtain a fluctuation scale and therefore assign a statistical value. The result of the three spatial scales was a correlation of 0.8, which they had never found with tropical diseases.
“This is the first time there is such a high correlation of tropical diseases with the weather. Although this does not mean causality, the degree of association between the indexes represented by the El Niño phenomenon with dengue cases in Colombia is quantified,” said UNal-Medellín Professor and member of the Intergovernmental Panel on Climate Change (IPCC) Germán Poveda Jaramillo.
Although dengue is a multicausal disease, the variability associated to ENSO explains the outbreaks in the country. In fact, its occurrence is also related with vectorial transmission in Colombia. Precisely twenty years ago a research group headed by Poveda, discovered that the El Niño phenomenon also has an impact on malaria intensification in Colombia.
For leishmaniasis and its relation to climate variability, the increased amount of cases in its different clinical forms also lags the warmer ENSO stage, with a 3 month delay in the Provinces near the Pacific coast (Chocó and Valle), and a high correlation with a 8 and 9 month lag to the climatic event in farther Provinces (Tolima and Caldas).
Despite that this disease is considered zoonotic, in other words, there is a relation between wild animals which host the parasite and the Lutzomyia insect; since twenty years ago there have been cases near urban areas (near the municipality of Ovejas -Sucre). Therefore, Acosta carried out her field work and analyzed the habits of 150 families and diverse ecological factors which may be bioindicators for the development of these insects in urban areas.
“The most important is the presence of the insect for disease transmission. Animals arrive because people take them there or are displaced due to deforestation. Additionally this disease could also be anthropozoonotic, in other words where human beings could also participate as parasite reservoir for the insect,” said Horacio Cadena Peña, Coordinator of the Eco-epidemiology Unit of the Universidad de Antioquia’s Tropical Disease Study and Control Program.
“Mosquitos are climbing the altitudinal range. They are now found beyond 2,300 meters above sea level (7,545 ft.). Therefore the diseases they transmit are spreading, among other reasons due to deforestation and climate change,” said Poveda.
Therefore the discoveries of Acosta help authorities structure prevention and control campaigns as well as early alert systems.
Agencia de Noticias UNAL |