Reports of malaria are increasing in many countries and in areas thought free of the disease. One of the factors contributing to the reemergence of malaria is human migration. People move for a number of reasons, including environmental deterioration, economic necessity, conflicts, and natural disasters. These factors are most likely to affect the poor, many of whom live in or near malarious areas. Identifying and understanding the influence of these population movements can improve prevention measures and malaria control programs.

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Malaria on the move: human population movement and malaria transmission.

The quantification of malaria transmission for the classification of malaria risk has long been a concern for epidemiologists. During the era of the Global Malaria Eradication Programme, measurements of malaria endemicity were institutionalised by their incorporation into rules outlining defined action points for malaria control programmes. We review the historical development of these indices and their contemporary relevance. This is at a time when many malaria-endemic countries are scaling-up their malaria control activities and reconsidering their prospects for elimination. These considerations are also important to an international community that has recently been challenged to revaluate the prospects for malaria eradication.

https://www.thelancet.com/pdfs/journals/laninf/PIIS1473-3099(08)70069-0.pdf

Measuring malaria endemicity from intense to interrupted transmission

The Intergovernmental Panel on Climate Change concluded that there is “discernible evidence” that humans—through accelerating changes in multiple forcing factors—have begun to alter the earth's climate regime. Such conclusions are based primarily upon so-called “fingerprint” studies, namely the warming pattern in the midtroposphere in the Southern Hemisphere, the disproportionate rise in nighttime and winter temperatures, and the statistical increase in extreme weather events in many nations. All three aspects of climate change and climate variability have biological implications. Detection of climate change has also drawn upon data from glacial records that indicate a general retreat of tropical summit glaciers. Here the authors examine biological (plant and insect) data, glacial findings, and temperature records taken at high-elevation, mountainous regions. It is concluded that, at high elevations, the overall trends regarding glaciers, plants, insect range, and shifting isotherms show remarkable intern...

Biological and Physical Signs of Climate Change: Focus on Mosquito-borne Diseases

A review of the life history of Plasmodium malariae, the quartan malaria parasite of humans, is presented. Much of the information is based on data obtained from induced infections in humans who were given malaria therapy for the treatment of neurosyphilis between 1940 and 1963. Prepatent periods (i.e., the time until the first day of parasite detection) fever episodes, and maximum parasitemias as a result of infection with P. malariae were obtained and are presented. Experimental and known vectors of the parasite are also discussed. Splenectomized chimpanzees and New World monkeys are readily infected and serve as sources of parasites and antigens for diagnostic and molecular studies. South American monkeys are naturally infected with a parasite known as Plasmodium brasilianum. This parasite appears to be P. malariae that has adapted from humans to grow in monkeys, probably within the last 500 years. Infection with P. malariae is associated with the production of immune complexes in the kidneys and the associated nephrotic syndrome. The essential lesions are a thickening of the glomerular basement membrane and endocapillary cell proliferation. Studies of monkeys infected with P. malariae indicate the same pathology as that demonstrated in humans.

Plasmodium malariae: Parasite and Disease

Travel is a potent force in the emergence of disease. Migration of humans has been the pathway for disseminating infectious diseases throughout recorded history and will continue to shape the emergence, frequency, and spread of infections in geographic areas and populations. The current volume, speed, and reach of travel are unprecedented. The consequences of travel extend beyond the traveler to the population visited and the ecosystem. When they travel, humans carry their genetic makeup, immunologic sequelae of past infections, cultural preferences, customs, and behavioral patterns. Microbes, animals, and other biologic life also accompany them. Today's massive movement of humans and materials sets the stage for mixing diverse genetic pools at rates and in combinations previously unknown. Concomitant changes in the environment, climate, technology, land use, human behavior, and demographics converge to favor the emergence of infectious diseases caused by a broad range of organisms in humans, as well as in plants and animals.

Travel and the emergence of infectious diseases.

Between 18 June and 20 September 1986, 28 cases of Plasmodium vivax malaria were documented in Carlsbad, California, a coastal town north of San Diego. Malaria occurred in 1 local resident who had no risk factors, a second local resident who had traveled to a malarious area 9 months earlier, and 26 Mexican migrant workers (MWs). Among the 28 cases, 27 lived in a square mile marshy area where Anopheles hermsi, a newly described American species of the Anopheles maculipennis group, was known to be breeding. An investigation of MWs residing in the affected area was done to determine the extent of the outbreak and to identify risk factors for acquiring malaria. We interviewed and drew blood from 304 healthy MWs and 17 (65%) of the MWs with malaria. Fluorescent antibody titers to P. vivax greater than or equal to 1:256 occurred in 14 (82%) of the 17 MWs with malaria tested and 9 (3%) of the healthy MWs. The principal risk factor identified for contracting malaria was sleeping outside on a hillside adjacent to the marshy area. Malaria in a local resident with no malaria risk factors and the clustering in time and place of 26 cases suggest that P. vivax malaria was introduced and local transmission was sustained through several generations, producing the largest outbreak of introduced malaria in the United States since 1952.

Transmission of Plasmodium vivax malaria in San Diego County, California, 1986.

During 1974, 12 cases of Plasmodium vivax malaria were reported from an agricultural area in California's Sacramento Valley. At least three of these cases resulted from local mosquito transmission. The imported cases were in Punjabi immigrants except for one in an American-born visitor to the Punjab. This is the 11th reported outbreak of introduced malaria in the United States since 1952, and the first in California since 1957. A unique aspect of this outbreak is the likelihood that secondary transmission occurred. Extensive surveillance activities, including a house-to-house case-finding survey in a 15-square-kilometer area of suspected transmission, yielded no new malaria cases, but the activities may have increased awareness of malaria among both the medical community and the public, and thus facilitated the detection of later cases. The occurrence of local malaria transmission coincided with unusually high numbers of Anopheles freeborni. The increase in imported malaria cases probably reflects a resurgence of malaria in Punjab State, India.

An outbreak of introduced malaria in California possibly involving secondary transmission.

A malaria epidemic among heroin users.

Five Aotus monkeys and two chimpanzees were infected with Plasmodium malariae isolated from a patient who acquired her infection approximately 50 years ago. All animals were splenectomized. The chimpanzees supported the highest parasite densities of 22,271/microliters and 18,544/microliters. Three Aotus monkeys with a previous history of infection with P. vivax had maximum parasite counts of from 1,818/microliters to 2,909/microliters, whereas two monkeys not previously infected had maximum parasite counts of 6,908/microliters. The establishment of new isolates in these animals aides the development of diagnostic probes and the identification of areas of antigenic variation within the species.

Ronald R. Roberto

Papers

Transmission of Plasmodium vivax malaria in San Diego County, California, 1986.

An outbreak of introduced malaria in California possibly involving secondary transmission.

A malaria epidemic among heroin users.

The China I/CDC strain of Plasmodium malariae in Aotus monkeys and chimpanzees