MicrobiologyBytes: Microbiology Notes: Malaria: History Updated: October 22, 2004 Search

History and Distribution:

Malaria parasites have been with us since the dawn of time. They probably originated in Africa (along with mankind) and fossils of mosquitoes up to 30 million years old show that the vector for malaria was present well before the earliest history. From their origins in Africa, P.vivax and P.malariae were possibly brought to the New World by early trans-Pacific voyagers, and this trend for imported malaria continues to this day. P.falciparum may have come in consignments of slaves bound for the Spanish colonies. The Plasmodium parasites are highly specific, with man as the only vertebrate host and Anopheles mosquitoes as the vectors (1). This specificity of the parasites also points towards a long and adaptive relationship with our species.

Hippocrates was the first to describe the manifestations of the disease, and relate them to the time of year and to where the patients lived - before this, the supernatural was blamed. The association with stagnant waters (breeding grounds for Anopheles) led the Romans to begin drainage programs, the first intervention against malaria. The first recorded treatment dates back to 1600, where the bitter bark of the cinchona tree in Peru was used by the native Peruvian Indians. By 1649, the bark was available in England, as 'jesuits powder' (2) so that those suffering from 'agues' might benefit from the quinine it contained. Malaria in the UK (known as agues) would have been clustered around stagnant marshes, and the invading Roman soldiers would certainly have brought the disease with them. There have been no recent cases due to an infective mosquito bite received within the UK so this is certainly not an endemic region.

Not until 1889 was the protozoal cause of malaria elicited by Laveran working in Algeria, and only in 1897 was the Anopheles mosquito demonstrated to be the vector for the disease. At this point the major features of the epidemiology of malaria seemed clear, and control measures started to be implemented.

The discovery of the insecticide DDT in 1942 and its first use in Italy in 1944 made the ideal of global eradication of malaria seem possible. Subsequently, widespread systematic control measures such as spraying with DDT, coating marshes with paraffin (to block Anopheles mosquito larvae spiracles), draining stagnant water, and the widespread use of nets and cheap, effective drugs such as chloroquine were implemented - with impressive results.

Despite initial success, there was a complete failure to eradicate malaria in many countries due to a number of factors. Although technical difficulties such as vector and parasite drug resistance have played a part, the main failure to reduce the disease is probably due to social, and political factors preventing efficient application of control measures (1). The malaria control operation was criticised for being too much like a military operation, and the lack of explanations offered to the local populations meant that the control measures received little support or even downright opposition (3).

Thoughtless man-made irrigation schemes and dams provided new habitats for Anopheles, and resulted in 'man-made' malaria. The extension of urban areas lead to epidemics in the peripheries of the growing cities. Mass migrations of non-immune populations into endemic areas for political reasons further complicates matters. Africa, where the majority of malarial disease is manifest was not even included in the global control mechanism, as it had insufficient infrastructure to support the policy (4). Despite the setbacks, up until 1969, when the global eradication policy was finally abandoned, the following European countries had managed to completely eradicate their endemic malaria by interrupting transmission: Hungary, Bulgaria, Romania, Yugoslavia, Spain, Poland, Italy, Netherlands, Portugal.

From the early 1970's the malaria situation has slowly and progressively deteriorated, and reduced control measures between 1972 and 1976 due to financial constraints lead to a massive 2-3 fold increases in cases globally. Spraying never truly eradicated the mosquitoes anywhere, and the reduction in the more persistent P.vivax infections were much less than for P.falciparum - though the latter returned in much greater strength as control measures waned. The growing interchange of populations between malarious countries and malaria free countries is responsible for the continuous increase in the number of imported malaria cases in European countries, and causes serious concern because of possible epidemic focal resurgence in receptive areas such as the Mediterranean. Since 1976, several new pockets of malaria transmission have evolved, and a WHO 1980 report recommended that countries which had become non-malarious should maintain at least one malaria vigilance unit.

At present, at least 300,000,000 people are affected by malaria globally, and there are between 1,000,000 and 1,500,000 malaria deaths per year (5). Malaria is generally endemic in the tropics, with extensions into the subtropics. Malaria in travellers arriving by air is now an important cause of death in non malarious areas (6), and this is not helped by the common ignorance or indifference of travellers to prophylaxis (4). Distribution varies greatly from country to country, and within the counties themselves, as the flight range of the vector from a suitable habitat is fortunately limited to a maximum of 2 miles, not taking account of prevailing wind etc. The map indicates current distribution of indigenous malaria according to WHO:

Map

In 1990, 80% of cases were in Africa, with the remainder clustered in nine countries: India, Brazil, Afghanistan, Sri-Lanka, Thailand, Indonesia, Vietnam, Cambodia and China. Current data for Africa is unavailable. The disease is endemic in 91 countries currently, with small pockets of transmission in a further eight. P.falciparum is the predominant species, with 120,000,000 new cases and up to 1,000,000 deaths per year globally. It is the P.falciparum species which has given rise to the formidable drug resistant strains emerging in Asia. In 1989, WHO declared malaria control to be a global priority due to the worsening situation, and in 1993, the World Health Assembly urged member states and WHO to increase control efforts.

In Africa, malaria accounts for up to a third of all hospital admissions, and up to a quarter of all deaths of children under the age of 5. There are up to 800,000 infantile mortalities and a substantial number of miscarriages and very low birth weight (VLBW) babies per year due to the disease. The cost of malaria in economic terms is also high; treatment ranges in cost between $US 0.80 and $US 5.30 depending on local drug resistance, and the total cost in Africa is $US1,800,000,000 per year (5). A bout of malaria typically costs 10 working days, adding to the economic burden. In Africa it is estimated that an individual receives 40-120 infective mosquito bites per year, compared to only 2 per year in India (4). Bearing the figures for Africa in mind, it seems incredible that in 1969, global eradication was envisaged from a policy which effectively ignored Africa other than for a couple of pilot schemes.


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