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120 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS
FIGURE 2-4 Seasonal rainfall anomalies in the Horn of Africa, September 2006-January 2007.

animal RVF cases and traveled with Ministry of Health staff to hospitals that recently had admitted patients with suspected RVF, obtaining specimens for testing at KEMRI.

On December 21, KEMRI confirmed RVF virus infection in specimens taken from several patients in the Garissa district (WHO, 2007a). The Kenya Ministry

FIGURE 2-5 NDVI anomalies (A) and RVF calculated risk (B) in the Horn of Africa, January 2007. In (B), green identifies areas included in the NDVI-based RVF risk assessment (based on permissive permanent environmental features) and red indicates areas currently at elevated risk, based on persistence of positive NDVI anomalies over at least 3 months.

FIGURE 2-5 NDVI anomalies (A) and RVF calculated risk (B) in the Horn of Africa, January 2007. In (B), green identifies areas included in the NDVI-based RVF risk assessment (based on permissive permanent environmental features) and red indicates areas currently at elevated risk, based on persistence of positive NDVI anomalies over at least 3 months.

of Health initiated a response with international partners, including WHO, CDC, USAMRU-K, NAMRU-3, and the U.S. Department of Agriculture. An intensive social mobilization campaign began in northeastern Kenya in late December, along with a locally enforced ban on animal slaughtering over most of Eastern and North Eastern Provinces (animal vaccination began in January, but by then the epidemic was waning). NASA-GSFC/DOD-GEIS provided frequent, high-spatial-resolution risk assessment updates to facilitate targeted surveillance during the epidemic response.

Between November 30, 2006, retrospectively identified as the date of onset for the index case, and March 9, 2007, when the last case was identified, 684 cases with 155 deaths were reported in Kenya. North Eastern province, which includes the Garissa district, reported the most cases of affected provinces (N = 333). Smaller RVF epidemics in Somalia and Tanzania followed the Kenya outbreaks: in Somalia, 114 cases with 51 deaths were reported between late December 2006 and February 2007; in Tanzania, 264 cases with 109 deaths were reported between mid-January and early May.

122 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS

I RVF risk areas RVF endemic regions

FIGURE 2-6 USAMRU-K mosquito collection sites (blue dots) and RVF risk assessment, December 2006.

I RVF risk areas RVF endemic regions

FIGURE 2-6 USAMRU-K mosquito collection sites (blue dots) and RVF risk assessment, December 2006.

Chikungunya Fever Outbreaks in Kenya and Other Regions, 2004-2008

In July 2004, while East Africa experienced a severe drought, a public hospital in Lamu, a coastal island city of Kenya, noted a sharp increase in cases of acute febrile illness. Many patients reported joint pain and had negative malaria blood smears (Bedno et al., 2006). The Ministry of Health launched an outbreak

CLIMATE, ECOLOGY, AND INFECTIO US DISEASE 123

investigation, which was supported by USAMRU-K and the CDC's IEIP. Laboratory testing of outbreak specimens identified chikungunya virus as the cause. After the outbreak, a population-based serological study led by the Kenya Field Epidemiology Training Program estimated that 13,500 people, or 75 percent of the Lamu population, were infected (Sergon et al., 2008). In November, a chi-kungunya outbreak was reported in Mombasa, around 200 miles south of Lamu on the Kenya coast.

Though rarely fatal, chikungunya virus infection may cause prolonged and debilitating joint pain. The disease is endemic throughout much of tropical Africa, maintained by transmission cycles involving forest-dwelling Aedes mosquitoes and wild primates in which humans are infected incidentally. Urban Aedes aegypti and Aedes albopictus cause epidemics in tropical Asia without nonhuman hosts. The vectors in urban Lamu and Mombasa were thought to be peridomestic Aedes aegypti, which were found in unprotected domestic water sources that were not changed frequently because of water shortages during the drought. The outbreaks marked the first confirmation of chikungunya fever transmission in coastal Kenya.

Retrospective analysis of climate data preceding the Lamu outbreak (assumed to have begun in June 2004) showed anomalously warm, dry conditions over much of East Africa, but especially coastal Kenya, during May 2004 (Chretien et al., 2007). NDVI anomalies in Lamu were the most negative in the available record (1998-2003), reflecting substantially reduced rainfall. When the outbreaks occurred in Lamu and Mombasa, each city had experienced a cumulative rainfall deficit of approximately 100 mm compared to the average (see Figure 2-7).

The warm, dry conditions may have enabled the epidemic in two ways: unsafe domestic water storage practices, along with infrequent changes of water stores because of the drought, may have increased peridomestic Aedes vector abundance; and the warm, dry conditions may have enhanced Aedes vectorial capacity by decreasing the extrinsic incubation period (Watts et al., 1987).

Following the Kenya chikungunya fever outbreaks, the epidemics spread to other areas with susceptible human populations and competent vectors: to western Indian Ocean islands, including Reunion, where viral mutation may have facilitated adaptation to the highly efficient Aedes albopictus vector (Tsetsarkin et al., 2007) and more than 200,000 people likely were infected (WHO, 2006), and to India, which reported well over 1 million cases (Mavalankar et al., 2007).

Also, for the first time ever, chikungunya fever reached Europe. In a northeastern Italian province, public health authorities identified 205 cases during July-September 2007 (Rezza et al., 2007). The presumed index case developed symptoms after visiting relatives in an affected area of India. Local Aedes albopictus mosquitoes, an invasive species introduced into Italy around 1990 (tire importation is suspected as the mechanism), then propagated the epidemic. While the role of climatic conditions in the Italian outbreak is unclear, much of southern Europe had experienced an anomalously warm, dry summer (see Figure 2-8)

124 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS

124 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS

Cumulative Monthly Rainfall

— Cumulative Longterm Mean Monthly Rainfall ' Approximate Start of CHIK Activity

Cumulative Monthly Rainfall

— Cumulative Longterm Mean Monthly Rainfall ' Approximate Start of CHIK Activity

FIGURE 2-7 Cumulative monthly rainfall (dotted line) and long-term mean cumulative monthly rainfall (solid line) in Lamu and Mombasa. Vertical dashed line indicates approximate starting dates for the outbreaks (Lamu, June 2004; Mombasa, November 2004).

that, along with historically poor vector control, may have contributed to the abundance of mosquitoes in the affected area at the time of the outbreak (reported anecdotally; Rezza et al., 2007).

Developing Early Warning Systems for Extreme Weather-Linked Infections

In both the RVF and the chikungunya fever examples, climate appears to have interacted with other factors to facilitate the outbreaks (see Table 2-2), consistent with the "Convergence Model" of infectious disease emergence proposed by the Institute of Medicine's (IOM's) Committee on Microbial Threats to Health in the Twenty-First Century (Figure 2-9; IOM, 2003). For example, besides flooding of mosquito habitats, animal sacrificing and preparation practices may have

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