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Impact of Climate Variability on Malaria

Impact of Climate Variability on Malaria

By L. Delgado, K. Córdova, A. J. Rodríguez

In Venezuela, the re-emergence of some diseases could be associated with certain climatic phenomena (Boy, Girl, etc.) which has manifested itself in some regions of the country with a higher incidence of malaria, as has been happening in Sucre State (Delgado et al, 2003).

Recent Analysis of the Impact of Climate Variability on Malaria in Venezuela

Climate variability can affect Venezuelan public health in different ways, one of which is produced by the alteration of precipitation patterns, as well as temperature patterns and other climatic elements, which translates into possible increases in certain infectious diseases, particularly metaxenic.

In Venezuela, the re-emergence of some of these diseases could be associated with certain climatic phenomena (Niño, Niña, etc.) which has manifested itself in some regions of the country with a higher incidence of malaria, as has been happening in the Sucre State ( Delgado et al, 2003).

The epidemiological patterns of presentation of malaria in Venezuela are due to multiple factors such as:
- Host susceptibility
- Immune status
- Socio-cultural and economic aspects,
- The vector and the environmental factors linked to its life cycle and its ecology.
- Climate variability.

Figure 1. Annual Malaria Incidence in Venezuela and its relationship with the years of the ENSO phenomenon, 1951 - 2001 (Delgado et al, 2004).


Figure 1 shows how the two periods with the highest incidence of malaria in Venezuela, for the period 1951 - 2001, can be associated, among other factors, with the observed climatic variability. Indeed, the peak of malarial incidence in 1971 coincides with a strong Niña year, which in Venezuela is associated with an intensification of rains to the detriment of the frequency of rainfall in the second half of the year, while the two previous years were relatively drier (1969, El Niño strong and 1970 Neutral).

On the other hand, the epidemic registered between 1988 - 1991, which occurred mainly in Bolívar, could also have been related to climatic changes. The years 1986 and 1987 corresponded with the El Niño phenomenon, weak and strong, respectively, after which the change to La Niña occurred, weak in 1988 and moderate in 1989 and with a weak El Niño in 1990.

As is known, the Sucre State has been the first state with malaria incidence on some occasions, always remaining among the first 5 states with the highest API.

Making an analysis of the epidemiology of the disease and its relationship with climatic variability in the Sucre State in the last 15 years (1986-2000), associations and correlations have been found between cases of malaria and alternation of the Niño and Niña phenomena (Figure 2).

Figure 2. Quarterly malarial incidence in Sucre and its relationship with the years of the ENSO phenomenon, 1986 - 2000 (Delgado et al, 2004).


For the period 1986 - 2000, 64,803 malaria cases were reported in Sucre State (annual mean of 1,117 ± 951 [± SD]) with five relevant peaks:
- 1988: 1,512 cases
- 1990: 2,071 cases
- 1991: 4,165 cases
- 1997: 3,513 cases
- 2000: 5,011 cases.

Significant correlations (r2> 0.50, P <0.05) were found between the increase in malaria cases and La Niña phenomena (defined as mostly cold and rainy periods), for certain years of the period studied. (Figures 3 and 6). Those years with a non-significant correlation may have other more important associated factors than the climatic one (Figures 4, 5 and 7).

Figure 3. Malaria Incidence (Cases) in Sucre and its relationship with the years of the ENSO phenomenon, 1986 - 1988 (Quarters) (Delgado et al, 2004).


Figure 4. Malaria incidence (Cases) in Sucre and its relationship with the years of the ENSO phenomenon, 1988 - 1989 (Quarters) (Delgado et al, 2004).


Figure 5. Malaria incidence (Cases) in Sucre and its relationship with the years of the ENSO phenomenon, 1990 - 1993 (Quarters) (Delgado et al, 2004).


Figure 6. Malaria incidence (Cases) in Sucre and its relationship with the years of the ENSO phenomenon, 1994 - 1996 (Quarters) (Delgado et al, 2004).


Figure 7. Malaria incidence (Cases) in Sucre and its relationship with the years of the ENSO phenomenon, 1998 - 2000 (Quarters) (Delgado et al, 2004).


The La Niña phenomenon in Venezuela, according to local climatic records and NOAA studies, is associated with a greater intensity of rainfall in the North-Central regions of the country. The increase in these precipitations is also related to periods of increase in the number of malaria cases after these elevations (Figure 8).

Climate changes certainly impact the biology and ecology of the vector, which is partly explained by the shortening of the life cycle, due to temperature, precipitation and humidity (aquatic phase), as well as a better life expectancy (phase terrestrial) (adult). Thus, the population of vectors increases, which, together with other biological and social factors predispose to an increase in the number of malaria cases, which is reported in the literature as well as in the studies carried out in the State. Sucre.

All of this shows the multifactorial characteristic of malaria and the complexity of this ecological system, where the climate is an important factor to consider and study.

Figure 8. Relationship between Malaria Dynamics in Sucre State, Venezuela and Climate Variations, 1986 - 2000 (Quarters) (Delgado et al, 2004).


Legend:
Top line: ENSO Climate Variations.
Red line: Incidence of Malaria cases by quarters / year
Blue line: Precipitation by quarter / year
Yellow Arrows: Possible connections between malaria incidence and rainfall.

* Climate and Health Project, CHIEX-Venezuela

REFERENCES

Cordova. Yes, Karenia. (2002) Socio-environmental impacts of climate variability in Venezuela.

Delgado L, Córdova K, Rodríguez AJ. (2003). Climate Variability and Health in Venezuela: Study of the dynamics of Malaria in Sucre State. In: V Venezuelan Congress of Ecology, Isla de Margarita, Venezuela, November; pp. 71.
Delgado L, Córdova K, Rodríguez AJ. (2004). Epidemiological Impact of Climatic Variation on Malaria Dynamics in a Northeastern Region of Venezuela. International Journal of Infectious Diseases 2004; 8 (Suppl 1): S23-S24.


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