Environment and Systemic Protozooses

Environment and Systemic Protozooses

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Within the framework of global changes, the El Niño-Southern Oscillation (ENSO) phenomenon has been associated with epidemic outbreaks of the disease. This article reviews the most important aspects of this relationship.

I. Climate Variability and its Incidence in Malaria

Malaria continues to be the most important infectious tropical parasitic disease in Venezuela, affecting rural areas of Bolívar, Sucre and Amazonas states, among others. The importance of climatic variability and its incidence in the disease has recently been studied, which is related to different climatic elements that impact the biology of the vector and its transmission. Within the framework of global changes, the El Niño-Southern Oscillation (ENSO) phenomenon has been associated with epidemic outbreaks of the disease. This article reviews the most important aspects of this relationship between a component of the environment (climate) and such an important systemic protozoosis, such as malaria. Key Words: Malaria, Ecoepidemiology, Climate Variability, Environment.


Malaria continues to be one of the most important vector-borne (metaxenic) diseases worldwide, and it continues to be the most important parasitic disease in Venezuela, particularly in endemic states, such as Sucre, Bolívar and Amazonas.

According to figures from the World Health Organization (WHO), an estimated 2.4 billion people live in malarious regions (WHO, 2004). Furthermore, each year 300 - 500 million people acquire the disease and more than one million children die from it (RBM, 2004).

In relation to the American continent, according to data published by the Pan American Health Organization (PAHO), malaria transmission continues to be reported in 21 countries of the Region and it is estimated that 175 million people live in areas with some risk of transmission .

For the year 2002, a total of 884,374 cases of malaria were reported (29,491 [3.34%] corresponded to Venezuela) (PAHO, 2003), a figure that has been similar in previous years. In countries where there is no longer transmission (areas of Central America and the Southern Cone), approximately 87 million people live in areas where transmission occurred previously and where there is currently an extremely low risk of transmission. The 262 million people who lived in areas with some potential risk of transmission represent approximately 31% of the 849 million inhabitants of the Region. This information, provided by the countries, contrasts with that corresponding to the year 2001, according to which 35% of the 835 million inhabitants of the Region lived in areas with some risk of transmission. In the 21 countries where malaria transmission occurs, 15% of the population lives in areas of high and moderate transmission, and 21% in low-risk areas. The percentage of national populations at risk ranges from 9% in Argentina to 100% in the Dominican Republic and El Salvador. Honduras, Mexico, Ecuador, and Panama reported that more than 15% of their populations live in high-risk areas. Cases reported by countries reached their lowest level in the past decade, and so did the number of blood smears examined. The rate of positive smears and the detection of cases in malarial areas were higher than in the previous year. Of the 21 countries where transmission occurs, 11 are in South America: Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guyana, Guyana, Paraguay, Peru, Suriname, and Venezuela. The other ten countries are in Mesoamerica: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua and Panama, along with the Dominican Republic and Haiti, the only two countries in the Caribbean where there is transmission (PAHO, 2003).

According to the Ministry of Health and Social Development (MSDS, 2003) in 2003, a total of 31,186 cases of malaria were reported (epidemic situation according to the endemic channel), of which 13,892 corresponded to the Bolívar state (Epidemic) , followed by Amazonas with 9,262 cases (Epidemic), Sucre with 5,266 (Security) and Delta Amacuro with 1,489 cases (epidemic outbreaks during several months of the year). Additionally, 533 imported cases from other countries must be added to the total number of cases originating in Venezuela, which totals 31,719 cases.

Fortunately, of the total number of cases observed in 2003, 82.6% corresponded to P. vivax infections, 16.7% to P. falciparum, 0.1% to P. malariae and 0.6% to P. vivax and P. falciparum (mixed infections).

The Annual Parasitic Incidence due to Malaria (IPA) for the year 2003 in Venezuela was 1.2 cases per 1,000 inhabitants.

These epidemiological data show the importance of the disease, which is associated with multiple factors, one of which is climate variability.

Ecoepidemiology and Disease Control

Malaria can be defined ecoepidemiologically as a complex public health system, made up of a series of interrelated and interdependent factors, where we find man (susceptible host) in the center of the ecoepidemyopathological and nosographic map, but considering various factors of the same host as well as the vector and its environment.

This pattern has changed a lot in terms of understanding and handling in the last 50 years. Between the 1940s and 1950s, several important events occurred. In 1945, the introduction of DDT in the disease control campaigns; in 1948, the implementation of Chloroquine as a first-line drug in the treatment of the disease and finally in 1950, the adoption of the Global Eradication Strategy (Sachs and Malaney, 2002). The latter constituting a failure, for which it ceased to apply. After the global abandonment of the program to eradicate malaria, the countries of America adopted the Global Strategy for Malaria Control in 1992, which is based on the following principles: early diagnosis and immediate treatment of the disease; the application of measures to protect and prevent the disease; the development of the capacity to predict and contain epidemics, and the strengthening of local capacity in basic and applied research to allow and promote the regular assessment of the malaria situation (PAHO, 2002).
Malaria is a priority of the World Health Organization. Along with HIV / AIDS and TB, Malaria constitutes a group of entities to which resources and particular attention are being devoted, which is why the Global Fund to Fight HIV / AIDS, TB and Malaria was created ( Global Fund against HIV / AIDS, TB and Malaria, GFATM) which is concerned as an entity to specifically fight against these three global epidemics (GFATM, 2003).

Factors Associated with Malaria

There are three large groups of factors currently related to the problem of malaria (Miller, 2002): Host factors (immunity, cytokines, genetics, age, pregnancy); Parasite Factors (resistance, multiplication, invasion routes, cytoadherence, rosetting, polymorphisms, antigenic variation, toxins); and Socioeconomic and Geographic Factors (access to treatment, cultural and economic factors, intensity of transmission, environmental and climatic factors).

The climatic factor has been recognized for some years since it has been established that malaria transmission is sensitive to changes in climate and the environment. In fact, malaria is currently perceived as the metaxenic disease most likely to be affected by global climate change (WHO / WMO / UNEP, 1996; McMichael et al., 1996). For these reasons, it is essential to study in detail and in an integrated way, with the help of different scientific disciplines, the impact and importance of changes and climate variability on malaria.

Climate Change and Perception of its Impact on Malaria

A changing climate is a factor prone to changing the dynamics of malaria transmission in many regions.

The gradual increases in malaria, worldwide, as well as the reinfestation of territories where the disease was previously controlled (e.g. the United States has recently reported autochthonous transmission of P. vivax by the vector Anopheles quadrimaculatus in the state of Florida) ( International Society for Infectious Diseases, 2003; CDC, 2003), are reasons to revitalize efforts in its control.

WHO has recently launched a new initiative to combat the aforementioned global malaria mortality and morbidity. The Roll Back Malaria initiative is being implemented in the countries most affected by the disease, with funding from the World Bank and other international agencies.

The cost of increasing effective insecticides and the development of in vitro and in vivo resistance to antimalarial drugs are probably the most important factors contributing to the prevalence of increased malaria in the coming decades. Therefore, efforts should be aimed at control, in high-risk years, increasing the cost-effectiveness of malaria control and making a more judicious use of insecticides that may delay the development of resistance to them. Therefore, the early detection of epidemics are, among others, the main global efforts for malaria control.

Today, it is known that malaria is specifically affected by various climatic factors, such as rainfall and temperature, among others. These are critical factors or parameters related to the transmission of the disease (Bouma, 1995).
These factors also have a dynamic, changing and additionally different behavior according to the geographical region, for which the study of them must tend to be specific and individualized.

In areas where malaria occurs there is considerable variation in the intensity of transmission and the risk of malaria infection. The high altitude areas (> 1500 masl) and arid type (<1000 mm rainfall / year) typically have less malaria, although these are prone to epidemic outbreaks when parasithemic individuals provide a source of infection and favorable climatic conditions for development occur. of the vector (Bloland, 2001, WHO, 1996).
Certain reports have been indicating the impact that environmental changes, particularly the El Niño phenomenon, would have on the development of epidemic outbreaks (Bouma & van der Kaay, 1994) and even the incidence of malaria in elevated areas, defined as malaria from height (Lindblade et al., 1999, US Naval Medical Research, 1999). Venezuela has not escaped this situation and there are reports that highlight the impact of weather phenomena such as El Niño and events related to it (eg La Niña) on the incidence of malaria (Bouma & Dye, 1997, Gagnon et al. ., 2002). Historical and recent data from Venezuela indicated that malaria could increase by approximately one third in the year following the El Niño event (Boumma & Dye, 1997) and, as has been described, climatic conditions could occur after this phenomenon. appropriate for the onset of malaria (Lindblade et al., 1999, Garnham, 1945, US Naval Medical Research, 1999).

The influence of the Inter-Tropical Convergence Zone (ITCZ) or ITCZ ​​(Inter-Tropical Convergency Zone) must also be taken into consideration. The ITCZ ​​is a strip of low pressures located in the equatorial zone, where the trade winds from the southeast and northeast converge. Due to the high temperatures, the air masses are forced to rise, causing abundant cloudiness as well as heavy precipitation, occasionally, also accompanied by electrical discharges. The ITCZ ​​is not uniform or continuous, it can be interrupted and its thickness and behavior vary from one place to another depending on the continentality or proximity of the sea (RAM, 2003).

The Phenomenon of the Child

To talk about the "El Niño" phenomenon, we must first explain what concerns the current "El Niño". This is a current of warm waters, directed towards the South, that occurs annually in the sea, off the arid coasts of South America and that at the end of the year causes a summer with rains.

To determine its magnitude, the so-called Southern Oscillation Index is used, which is the difference in atmospheric pressure between the Eastern Pacific (Tahiti) and the Western Pacific (Darwin). If the index is negative (warm phase) it generates, although not necessarily, the presence of 'El Niño'.

Thus the phenomenon "El Niño", also known by the scientific name of "El Niño - Southern Oscillation" (ENSO); it is a large-scale event, extending beyond the South Pacific. The El Niño Phenomenon is the generalized increase in the temperature of the sea surface in a large part of the Eastern and Central sector of the Equatorial Pacific. It is also associated with a decrease in atmospheric pressure in the Eastern South Pacific (coast of South America) and with an increase in the Oceania region (MinAgriCultura, 2004).

Given the importance of studying global climate change and its effect on society, there are many agencies in charge of monitoring the dynamics of these environmental factors. In the "on-line" systems of the Climate Prediction Center of the National Oceanographic and Atmospheric Administration (NOAA, 2004), the El Niño and La Niña episodes can be observed by season for each year These climatic phenomena are classified by a series of criteria: Some classification systems use the Southern Oscillation Index (SOI), while others use the Sea Surface Temperature ( SST) Recently, a "consensus" list of El Niño / La Niña years has been established (Null, 2003).

Climate Impacts in South America on Malaria

In many parts of South America the impacts of these climate anomalies related to ENSO have been observed. Many epidemics in the northern countries of South America have occurred one year after the El Niño phenomenon. The malaria epidemics observed in 1983 in Ecuador, Peru and Bolivia were associated with intense rains, in turn associated with a strong El Niño event that occurred in 1982-1983 (Cedeño, 1986; Russac, 1986; Nicholls, 1993).

In the case of Ecuador, the malaria epidemic was exacerbated by the population displacement that caused the landslide.

The relationship between ENSO and malaria has been and continues to be evaluated by many authors, in detail for several countries in South America (Bouma and Dye, 1997; Bouma et al., 1997b; Poveda and Rojas, 1996; 1997; Delgado et al, 2003; 2004).

These countries usually have below-average rainfall during El Niño. Some studies have tried to establish, for example, that in Venezuela malaria increases by 37% in the post-child year, but although this is a currently poorly supported figure, it is true that during a year after El Niño, usually It tends to alternate with a La Niña year, during which rainfall increases, giving a favorable climate for the development of wetlands and breeding sites for the anopheline mosquito, increasing transmission in susceptible places and thus increasing the incidence of malaria ( Bouma and Dye, 1997; Bouma et al., 1997b; Poveda and Rojas, 1996; 1997; Delgado et al, 2003; 2004).

In other countries, such as Colombia, malaria cases increase by 17.3% during El Niño and by 35.1% during the post-child year (Bouma et al., 1997b; Anon, 1996). In Colombia, El Niño is associated with a reduction in normally high rainfall in most of the country (Poveda and Mesa 1997).

These changes can produce an increase in the number of hatcheries (Poveda et al., 1999a). High temperatures during El Niño events can favor malaria transmission (Bouma et al., 1997b; Poveda et al., 1999b).

The exact reasons why malaria increases after a dry period are not fully understood, in particular, in the absence of a subsequent rainy period that explains the increase in the abundance of breeding sites and hence the disease.
An important point to consider is the difference that is established in the expression of climatic phenomena according to each country and even each region in particular.

Climate changes must be properly analyzed, since the increases in malaria cases in the years that followed the El Niño events, reported by Bouma (1997) are not constant.

Development of Malaria Prediction Systems Based on Climatic Signs and Data

It is necessary to develop surveillance systems that make it possible to make predictions of the trend of the disease from climatological records, in order to make predictions several days in advance and thus predict and prevent epidemic outbreaks to reduce or mitigate their effects ( Cresswell et al, 1998).

Currently in Africa, the working group MARA (Mapping Malaria Risk in Africa) is in charge of assessing malaria risk based, on the one hand, on environmental changes, especially climate, through satellite images and, on the other, on aspects epidemiological (MARA / ARMA, 2004).

The improvement of geospatial technologies has led to a more accurate evaluation of public health problems at different scales, especially in tropical diseases, such as malaria, dengue, cholera, among other metaxenic and hydric diseases. Different sources of information have been integrated, including Global Positioning Systems (GSP) and Geographic Information Systems (GIS). These technologies have changed the way of approaching problems in tropical medicine and in international health. The way of looking at the epidemiology of tropical diseases has changed thanks to these technologies. Their applications in Venezuela are limited to academic and research institutes, but in a few years they will be widely used by government health agencies responsible for the control of these diseases throughout the country (Delgado et al, 2004b).

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 in temperature patterns and other climatic elements (among them relative humidity, wind and insolation) , which can increase certain infectious diseases, particularly metaxenic ones.

In Venezuela, the re-emergence of some of these diseases could be associated with certain climatic phenomena (El Niño, La Niña, among others), which has been evidenced in some regions of the country with a higher incidence of malaria, as has occurred in the Sucre State (Delgado et al, 2003; Córdova 2003).

The epidemiological patterns of malaria expression in Venezuela are due to multiple factors, such as: susceptibility of the host, its immune status, socio-cultural and economic aspects, the biology of the vector and environmental factors related to its life cycle and its ecology. .

The two historical periods with the highest incidence of malaria in Venezuela, for the period between 1951 and 2001, have corresponded to an association with climatic phenomena. During the peak observed in 1971 (strong La Niña year) the previous two years were relatively drier (1969, Strong El Niño, and Neutral 1970).

As is well known, the Sucre State has been, on some occasions, the first state in malaria incidence at the national level, always remaining among the first 5 states with the highest annual parasite rates (API).

Making a detailed analysis of the epidemiology of the disease and its relationship with climate variability in the Sucre State during the last 15 years (1986-2000), associations and correlations have been found between cases of malaria and alternation of the El Niño and El Niño phenomena. The girl.

In this time series, significant correlations (r2> 0.50; p <0.05) were found between the increase in malaria cases and La Niña phenomena (defined in this case as mostly cold and rainy periods) , for certain years of the period studied. Those years with a non-significant correlation may have other more important associated factors than climate.

On the other hand, the 1988 - 1991 epidemic, which occurred mainly in Bolívar, could be 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 then a weak El Niño in 1990.

When we observe the incidence of malaria during El Niño years and those years that do not correspond to this phenomenon, we can see that there are statistically significant differences in the increase above the trend of cases during the years other than El Niño and a decrease during the years El Niño itself, which is seen more markedly during the last quarters of the year (Figure 1).

The La Niña phenomenon in Venezuela, according to the United States agency, National Oceanographic and Atmospheric Administration (NOAA), is associated with a greater intensity of rainfall in the North-Central regions of the country. The increase in these precipitations is associated with periods of increase in the number of malaria cases after these elevations.


As has been established, climatic 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 (terrestrial phase) (adult). Thus, the vector population 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 that are being carried out in Sucre State.

All of this highlights the multifactorial characteristics of malaria (Sachs & Malaney, 2002) and the complexity of this ecological system, where the climate is an important factor to consider and study, but even more, to monitor to develop prevention systems and containment of the disease, thus improving its understanding and integrated care.

* 1Fellow of the Royal Society for Tropical Medicine & Hygiene, Member of the International Society for Infectious Diseases. 2Postgraduate Students, 3Postgraduate Professors, Master in Protozoology, CTIPjwT-NURR-ULA. 4Researcher and Professor at the Institute of Tropical Zoology, Faculty of Sciences, UCV. 5Researcher and Professor at the Institute of Geography and Regional Development, Faculty of Humanities and Education, UCV. * Researchers of the Climate and Health Project in Venezuela, CHIEX-CRN-IAI. URL: E-mail: [email protected]


The research works on Climate and Health of A. J. Rodríguez Morales, L. Delgado and K. Córdova are partially funded by the Inter-American Institute for Global Changes Research (Program CRN) (YRP).
Review carried out during the Climatology and Soil Study Unit, Master's Degree in Protozoology, Trujillano Center for Parasitological Research José Witremundo Torrealba, Rafael Rangel Nucleus, Universidad de Los Andes, Trujillo. Finally, the constant collaboration of the General Directorate of Environmental Health and Sanitary Comptroller (Malariology) of the Ministry of Health and Social Development, in the person of Dr. Darío González, is appreciated.

Figure 1. Deviation from the trend in malaria cases during El Niño and non-El Niño years (%), by quarters, Sucre State, Venezuela, 1986-2000. (Bars: Mean ± SD)

* By Alfonso J. Rodríguez Morales, M.D., 1,2 * Rocio Cárdenas, Bacteriol.B.Sc., 2
Claudia Sandoval, Biol.B.Sc., 2 Gerardo Baptista, Pharm.D., 2 Edgar Jaimes, Ph.D., 3 José Gregorio Mendoza, M.Sc., 3 Laura Delgado, Ph.D., 4 * and Karenia Córdova, M.Sc.5 *

1 Fellow of the Royal Society for Tropical Medicine & Hygiene, Member of the International Society for Infectious Diseases. 2 Postgraduate Students, 3 Postgraduate Professors, Master in Protozoology, CTIPjwT-NURR-ULA. 4 Researcher and Professor at the Institute of Tropical Zoology, Faculty of Sciences, UCV. 5 Researcher and Professor at the Institute of Geography and Regional Development, Faculty of Humanities and Education, UCV. E-mail: [email protected]

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Páginas Web Recomendadas sobre Variabilidad Climática y Malaria:
Climate and Health Exchange Network
Roll Back Malaria (RBM) – World Health Organization (WHO)
Program for Research and Training in Tropical Diseases (TDR) (WHO)
Inter-American Institute for Global Change Research
Malaria International Foundation
Organización Mundial de la Salud
Organización Panamericana de la Salud
Organización Meterológica Mundial
Climate Modeling and Diagnostics Group
Climatic Research Unit
NOAA-NWS Climate Prediction Center
IRI/LDEO Climate Data Library
International Society for Biometeorology

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