Developing global climate anomalies suggest potential disease risks for 2006 – 2007

Background El Niño/Southern Oscillation (ENSO) related climate anomalies have been shown to have an impact on infectious disease outbreaks. The Climate Prediction Center of the National Oceanic and Atmospheric Administration (NOAA/CPC) has recently issued an unscheduled El Niño advisory, indicating that warmer than normal sea surface temperatures across the equatorial eastern Pacific may have pronounced impacts on global tropical precipitation patterns extending into the northern hemisphere particularly over North America. Building evidence of the links between ENSO driven climate anomalies and infectious diseases, particularly those transmitted by insects, can allow us to provide improved long range forecasts of an epidemic or epizootic. We describe developing climate anomalies that suggest potential disease risks using satellite generated data. Results Sea surface temperatures (SSTs) in the equatorial east Pacific ocean have anomalously increased significantly during July – October 2006 indicating the typical development of El Niño conditions. The persistence of these conditions will lead to extremes in global-scale climate anomalies as has been observed during similar conditions in the past. Positive Outgoing Longwave Radiation (OLR) anomalies, indicative of severe drought conditions, have been observed across all of Indonesia, Malaysia and most of the Philippines, which are usually the first areas to experience ENSO-related impacts. This dryness can be expected to continue, on average, for the remainder of 2006 continuing into the early part of 2007. During the period November 2006 – January 2007 climate forecasts indicate that there is a high probability for above normal rainfall in the central and eastern equatorial Pacific Islands, the Korean Peninsula, the U.S. Gulf Coast and Florida, northern South America and equatorial east Africa. Taking into consideration current observations and climate forecast information, indications are that the following regions are at increased risk for disease outbreaks: Indonesia, Malaysia, Thailand and most of the southeast Asia Islands for increased dengue fever transmission and increased respiratory illness; Coastal Peru, Ecuador, Venezuela, and Colombia for increased risk of malaria; Bangladesh and coastal India for elevated risk of cholera; East Africa for increased risk of a Rift Valley fever outbreak and elevated malaria; southwest USA for increased risk for hantavirus pulmonary syndrome and plague; southern California for increased West Nile virus transmission; and northeast Brazil for increased dengue fever and respiratory illness. Conclusion The current development of El Niño conditions has significant implications for global public health. Extremes in climate events with above normal rainfall and flooding in some regions and extended drought periods in other regions will occur. Forecasting disease is critical for timely and efficient planning of operational control programs. In this paper we describe developing global climate anomalies that suggest potential disease risks that will give decision makers additional tools to make rational judgments concerning implementation of disease prevention and mitigation strategies.

other regions will occur. Forecasting disease is critical for timely and efficient planning of operational control programs. In this paper we describe developing global climate anomalies that suggest potential disease risks that will give decision makers additional tools to make rational judgments concerning implementation of disease prevention and mitigation strategies.

Background
The El Niño/Southern Oscillation (ENSO) is the most well-known phenomenon influencing the global climate variability at interannual time scales. The National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC) has recently issued an unscheduled El Niño conditions advisory that indicates that El Niño conditions will peak during the Northern Hemisphere winter, followed by weakening during March -May 2007 [1]. The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea surface temperatures across the central and east-central equatorial Pacific (between approximately the International Date line and 120 degrees west longitude), and thus represents the warm phase of the ENSO, and is sometimes referred to as a Pacific warm episode. The opposite of which is La Niña, a cold phase of ENSO. Given the large size of the Pacific Ocean, changes in the sea surface temperature patterns and gradients across the basin influence atmospheric circulation with pronounced impacts on global tropical precipitation and temperature patterns.
Climate variability has a demonstrated impact on infectious diseases [2], and increased disease transmission has been linked to ENSO driven climate anomalies [3][4][5][6][7]. Outbreaks of insect transmitted diseases such as Murray Valley encephalitis, bluetongue, Rift Valley fever (RVF), African Horse sickness, Ross River virus disease [8][9][10][11][12] and malaria [13,14] have been associated with El Niño. Hence, forecasting the risk of ENSO related human and animal disease outbreaks is critical for timely and efficient planning of operational control programs. However, for decision makers to respond effectively the forecast must be accurate and timely [5]. Here we describe developing global climate anomalies that suggest potential elevated disease risks in the hope that decision makers will have additional tools to make rational judgments concerning implementation of a wide-range of disease mitigation strategies. Using the 1997/98 period as a reference template ( Figure  4) and the forecast of likely conditions for the next 3-9 months, there is a high likelihood for drought conditions to prevail over south-east Asia, Mexico, north-east Brazil and Southern Africa, and above normal rainfall and flood conditions to occur over coastal Peru, southern California, the U.S. Gulf Coast and Florida and Eastern Africa.

Potential elevated disease outbreaks
Some of the above climate extremes are already being experienced in equatorial East Africa, Australia and the Indonesian Peninsula. These extremes in climatic conditions will likely affect vector abundance in different ways elevating the risk of outbreaks of various infectious diseases [3]. Drought conditions can suppress predators of Anopheles malaria vectors [14,16]; however, heavy rains will boost food supplies -a synergy that can for example elevate rodent populations [17] and create appropriate conditions for mosquito breeding and propagation [11]. Previous ENSO events have been strongly associated with disease outbreaks over time and with spatial clusters of mosquito-, water and rodent-borne illnesses. Given current observations and forecast information the following regions ( Figure 5) are at increased risk for disease outbreaks.
1. Indonesia, Malaysia, Thailand and most of the Southeast Asia Islands: Increased dengue fever transmission caused by drought conditions which (1) increase water storage around houses leading to elevated Aedes aegypti populations and (2) elevate ambient air temperatures which will reduce the extrinsic incubation period for the virus in vector mosquitoes increasing vector capacity [ [18], Linthicum et al., unpublished observations]; increased respiratory illness due to haze from uncontrolled burning of tropical forests when extreme drought occurs.
2. Coastal Peru, Ecuador, Venezuela, and Colombia: Increased risk of malaria due to elevated Anopheles vector populations which will develop when various types of immature habitats are flooded after heavy rainfall follows a period of drought [14,16].
3. Bangladesh and coastal India: Elevated risk of cholera due to elevated sea surface temperatures and of incursion of plankton-laden water inland rich in Vibrio cholerae, the bacterium that causes cholera [7]. In addition to elevated SSTs, heavy rains wash nutrients into waterways and may trigger plankton blooms. 4. East Africa (Ethiopia, Kenya, Somalia, and Uganda): Increased risk for RVF and malaria resulting from elevated mosquito vector populations, and cholera caused by flooding due to heavy rainfall in dry land areas [7,11,19,20]. 5. South West USA (New Mexico, Arizona): Increased risk for hantavirus pulmonary syndrome and plague due to elevated rodent populations caused by heavy rainfall [17,21] 6. Southern California: Elevated potential for transmission of arboviruses, such as West Nile virus, caused by heavy rainfall and resulting in elevated Culex species mosquito populations. 7. Northeast Brazil: Drought conditions leading to increased dengue fever and respiratory illness.

Discussion
Currently weak El Niño conditions exist, but there is a potential for this event to strengthen into a moderate event by winter.

Conclusion
An El Niño conditions advisory has been issued by the NOAA CPC which indicates that anomalously warm SST conditions exist in the equatorial Pacific in October 2006 and are likely to continue into early 2007 [1]. Global products including SST and OLR, which are useful in illustrating the current situation of global climate anomalies, are being monitored for their implications for public health [22]. Impacts of the current El Niño include above normal precipitation over the eastern Pacific and East Africa regions, and drier than average conditions over Southeast Asia, Malaysia and Indonesia. These conditions will likely persist for the remainder of 2006 and early 2007.
The development of El Niño conditions has significant implications for global public health. Extremes in climate events with above normal rainfall and flooding in some regions and extended drought periods in other regions will occur. Forecasted elevated rainfall in coastal Peru, Ecuador, Venezuela and Columbia will increase malaria risk due to elevated Anopheles vector populations. Heavy rainfall in East Africa may elevate mosquito vector populations and lead to RVF, and increased malaria and cholera risk. Elevated rainfall in the south west of the U.S. will increase the risk of the rodent-borne diseases hantavirus pulmonary syndrome and plague. Above normal rainfall in southern California will elevate the risk of West Nile virus. Elevated sea surface temperatures near Bangladesh and India will increase the risk of cholera. Drought conditions in Southeast Asia and islands of Indonesia and northeast Brazil will increase the risk of dengue fever and respiratory diseases.
Forecasting epidemics or epizootics is critical for timely and efficient planning of operational control programs if the forecast is accurate and delivered in a timely manner. In this paper we describe developing global climate anomalies that suggest potential disease risks so that decision makers will have supplemental tools to make rational judgments concerning implementation of a widerange of disease prevention and mitigation strategies.

Methods
We  Anomalous climatic conditions caused by ENSO are now recognized to be linked with outbreaks of various human and animal diseases in various countries [28]. The eco-climatic conditions associated with disease outbreaks can now be effectively monitored using satellite data as illustrated here.