encountered: P. malariae is found worldwide, and the geographic range of P. ovale is limited mostly to tropical Africa, the Middle East, southeast Asia, and the western Pacific.
Malaria infection occurs when a Plasmodium-infected Anopheles mosquito feeds on a susceptible human host, delivering sporozoites that initially invade hepatocytes and mature into merozoites that then invade erythrocytes. The cycle is completed when a competent female Anopheles mosquito feeds on a parasitemic human, obtaining gametocytes that then initiate infection in the mosquito. Many Anopheles species are potential vectors of malaria in different parts of the world, so mosquito species-specific behaviors, including host feeding preference and daily activity patterns, tend to result in varied regional transmission patterns. Often, several mosquito species will combine to constitute an overall vector profile for a region. In tropical areas, transmission intensity is often linked to rainy seasons—typically one major and another less severe. In temperate or seasonally arid regions, a single transmission period is evident (Guerrant et al. 1999).
The best recent estimates of overall malaria morbidity and mortality in southwest and south-central Asia are about 6 million cases and 59,000 deaths per year (RBM 2005a). Afghanistan and Yemen alone account for an estimated 5.5 million of all cases, on the basis of 2004 data (RBM 2005b). In the malaria-endemic countries of Tajikistan, Azerbaijan, Armenia, Georgia, Kyrgyzstan, and Uzbekistan, malaria occurred at a rate of 0.11 case per 1,000 population in 1990-2003 (RBM 2005h). In contrast, the case rate was about three per 1,000 during the same period in southwest Asia, Afghanistan, and Pakistan combined (RBM 2005h).
About 70% of all infections are caused by P. vivax, but this varies regionally. P. malariae is not reported to be endemic in most parts of southwest or south-central Asia and is rare in areas where it has been reported. Diagnosis and reporting in some areas, such as Iraq and Afghanistan, have been hindered in recent years because of war-related interruptions to the public-health infrastructure. Transmission is highly seasonal and peaks in late July to September.
In Iraq, malaria is endemic in Duhok, Erbil, Ninawa, Sulaimaniya, Tamim, and Basrah provinces. Some 362 cases were recorded in Iraq in 2003. The disease is due exclusively to P. vivax; peak transmission takes place in May-November. The main vectors are A. sacharovi, A. superpictus, A. maculipennis, A. stephensi, and A. pulcherrimus. Most of the cases occur in the northern governorates, mainly in the Zakho district in Dohuk, where four of the five vector species reside (RBM 2005e).
Malaria is endemic in Afghanistan in all areas below 2,000 m in altitude. Afghanistan reported about 600,000 cases in 2003, 93% of which were caused by P. vivax and 7% by P. falciparum (Kolaczinski et al. 2005). Estimates of the rates of feeding of infective vectors on humans in eastern Afghanistan indicated that A. stephensi would contribute 76% of infective bites and A. fluviatilis and A. culicifacies 7% and 3%, respectively. Because of chloroquine resistance, numbers of P. falciparum infections in eastern Afghanistan have increased from 1% of all infections in 1970 to 20% in 2002 (Kolaczinski et al. 2005; RBM 2005c).
Saudi Arabia tends to have equal percentages of infection with P. vivax and P. falciparum but low case totals (1,700 cases in 2003). The primary vector in Saudi Arabia is A. arabiensis (RBM 2005g).