Malaria in Oases of Eastern Saudi Arabia

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Summary 1. Malaria has been an important health problem in the Qatif and al-Hasa oasis for centuries. The disease is sharply delimited to cultivated areas in the Eastern Province and affects the settled oasis population (310,000). The nomadic Bedouins are normally free of the disease. 2. Oasis malaria is man-made malaria and is directly connected with the local practice of agriculture. Local irrigation methods and drainage schemes furnish vector breeding places; hence malariousness of villages is directly dependent on their nearness to, and extent of, adjacent irrigated acreage. 3. Uncontrolled malaria may reach hyperendemic proportions. As such, it represents a major potential cause of morbidity and a ranking cause of mortality in the oases. Both industry and agriculture suffer when the disease is uncontrolled; and if these activities are to continue to prosper, adequate provision for malaria control must be made. 4. Precontrol morbidity (1941 through 1947) in adults was measured by cases reported in Saudi Arab employees of the Arabian American Oil Company. Annual attack rates varied from slightly over 1,000/10,000 in less malarious years to 2,300/10,000 in more malarious years. The mean annual morbidity rate in this group of adults was 1,631/10,000 during precontrol years. 5. Precontrol mortality (1941 through 1947) averaged 22/100,000 in the above employee group (only eight employee deaths). With 43 malaria deaths of patients from the general population occurring in Aramco hospitals during this same period, a proportionate mortality rate of 11.6 per cent was recorded. This rate was calculated from total deaths reported on death certificates in Saudi Arab employees, their dependents, and other non-Aramco members of the general public. 6. Precontrol malaria surveys (1947) in typical oasis villages in the Qatif area showed an average parasite rate (2–14-year age group) of 85 per cent. The infant parasite rate was 100 per cent. The gametocyte rate in the 0–11-month age group was 27 per cent; in the 12–23-month group, 24%; and for the 2–14-year composite, 13%. A comparable spleen rate in the 2–14-year age group was 94 per cent. Spleen rates increased with age; the reverse was true of parasite rates. The average spleen size was 2.2, average enlarged spleen was 2.3, and splenometric index was 217.1 in the 2–14-year age group. These data emphasize the public health importance of malaria in these oases. 7. Falciparum malaria was predominant over vivax and malariae, both in available adult morbidity data and in village parasite surveys of children. From original Qatif surveys in typical oasis villages, the 85 per cent parasite rate consisted of falciparum, 35.5 per cent; vivax, 27.4 per cent; malariae, 14.2 per cent; species undetermined, 1.2 per cent; and mixed infections, 6.6 per cent. The same general proportionate species distribution occurred among employee cases when species determinations were available. In earlier years, a majority of cases reporting to hospitals was determined as clinical malaria without reference to species of parasite. 8. The following anophelines occur in the area: A. stephensi, fluviatilis, pulcherrimus, sergenti, multicolor, and coustani var. tenebrosus. Of these stephensi is the only important vector; fluviatilis may be of secondary importance, but its role in local malaria transmission is unknown. 9. The local vector, Anopheles stephensi, is present in enormous numbers especially during spring and fall transmission seasons. It rests in man-made shelters during the day and is active in feeding only after sunset. Blood meal sources include a variety of warmblooded animals; but on the basis of limited precipitin test data, man is not the favored host. Stephensi accounts for 90.6 per cent of anophelines found in houses and for 79.3 per cent of anophelines recoverd from light-trap collections. The New Jersey electric mosquito trap has proved useful in local anopheline surveys. 10. Stephensi utilizes a wide variety of surface waters for breeding places. Among the more important are drainage ditches, seepage areas, ponds, shallow wells, borrow pits, and shallow puddles. Rice fields do not add appreciably to the local malaria problem. Artificial containers are of no local importance as stephensi breeding sites. High degrees of salinity and even some degree of pollution are not deterrents to breeding. 11. Local climate is characterized by extremely hot summers and temperate winters, with oppressively high humidity in late summer and early fall. Weather data from Aramco's Ras Tanura weather station were used in studying effects of climate on seasonal distribution of malaria and on vector densities. Mean weekly and monthly temperatures (1945–1956), mean weekly and monthly relative humidities (RH) based on 0900 readings (1945–1949), and on daily means (1949–1956) were calculated. Monthly rainfall data are available from 1945–1956. The average annual rainfall is 3.23 inches, occurring sporadically from November through May, with December having the highest average monthly rainfall (1.14 inches). Mean monthly temperatures for the 12-year period (1945–1956) ranged from a low of 60.7° F in January to highs of 92.5° F in July and August. Mean monthly RH based on 0900 readings (1945–1949) ranged from a low of 50.1 per cent in August to a high of 78.4 per cent in December. When calculated from daily means (1949–1956), mean RH ranged from a low of 53.8 per cent in June to a high of 73.3 per cent in February. With wide daily fluctuations in humidity, 0900 readings and subsequent calculations from them gave a more orderly seasonal progression and recession in RH. Hence the latter are recommended for any future analysis of RH. 12. Winter temperatures are low enough to inhibit, but not severe enough to stop, stephensi breeding. Spring and fall provide ideal conditions for development of...

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