Ross Establishes Malaria’s Transmission Vector

Several days after allowing mosquitoes to feed on a patient with malaria, Ronald Ross observed the malarial parasite in the stomach of the insect. He observed the parasite migrate to the salivary gland of the insect, suggesting a mechanism of transmission from human to human. Ross subsequently demonstrated that the anopheles species of the mosquito was the specific vector for transmission of the disease.

Summary of Event

Malaria is an ancient disease whose records go back to the time of the ancient Greeks. Greece, ancient;malaria in Moreover, indirect evidence suggests that the disease goes back several thousand years earlier in the eastern Mediterranean region. The earliest known direct description of malaria is in the writings of Hippocrates Hippocrates (c. 460-c. 370 b.c.e.), who described an illness with intermittent fever that appeared every three to four days and was generally found in people living near areas of dampness or swamps. From Greece, the disease spread to Rome, where its name was coined as a result of the belief that mala aria, or bad air, could be the cause. In 1740, Horace Walpole translated the Latin name into the English “malaria.” Malaria;transmission of
Ross, Ronald
Manson, Sir Patrick
Laveran, Alphonse
[kw]Ross Establishes Malaria’s Transmission Vector (Aug. 20, 1897)
[kw]Establishes Malaria’s Transmission Vector, Ross (Aug. 20, 1897)
[kw]Malaria’s Transmission Vector, Ross Establishes (Aug. 20, 1897)
[kw]Transmission Vector, Ross Establishes Malaria’s (Aug. 20, 1897)
Malaria;transmission of
Ross, Ronald
Manson, Sir Patrick
Laveran, Alphonse
[g]British Empire;Aug. 20, 1897: Ross Establishes Malaria’s Transmission Vector[6260]
[g]India;Aug. 20, 1897: Ross Establishes Malaria’s Transmission Vector[6260]
[c]Health and medicine;Aug. 20, 1897: Ross Establishes Malaria’s Transmission Vector[6260]
[c]Science and technology;Aug. 20, 1897: Ross Establishes Malaria’s Transmission Vector[6260]
Kelsch, Louis-Félix-Achille
Golgi, Camillo

By the period of the eighteenth century, theories about the source of the infection began to center on contaminated water. The germ theory of disease, primarily the result of research by Robert Koch Koch, Robert and Louis Pasteur Pasteur, Louis , resulted in physicians addressing the possibility of malaria being cause by a germ. The involvement of mosquitoes had historically aroused suspicion. Indeed, a description in Sanskrit literature from fifteen hundred years earlier had suggested a connection between mosquitoes and the disease, but until the nineteenth century, it was not believed that insects served as vectors of disease.

The first demonstration of the role played by parasites other than bacteria in disease came in 1878. Sir Patrick Manson, medical adviser to the British colonial office, reported the presence of the filarial worm in the blood of patients with elephantiasis, a condition marked by significant enlargement of the limbs. At the time, Manson failed to observe the maturation and development of the parasites he had observed, nor did he link the worm with its ingestion and passage through mosquitoes. He mistakenly continued to believe it was the ingestion of contaminated water that spread the disease, not the insect. However, as a result of his extensive studies into such diseases, Manson became known as the founder of tropical medicine, and later, more pejoratively, as Mosquito Manson.

Louis-Félix-Achille Kelsch Kelsch, Louis-Félix-Achille reported the presence of dark staining inclusion bodies in both red and white blood cells of persons with malaria. The significance of his observation was not understood immediately. In 1880, Alphonse Laveran, a French army surgeon stationed in Algeria, observed a spherical parasite containing hairs, or flagella. This parasite was likely the male gametocyte of the malarial protozoan, now known by the genus name Plasmodium. Émile Roux Roux, Émile , a pupil of Laveran while in military school, arranged for a demonstration of “Laveran’s bodies” to Roux’s skeptical associate, Louis Pasteur. The success of this work later resulted in a successful search for other plasmodia in birds. Several years later, Camillo Golgi Golgi, Camillo , more reknowned for his observation of cellular organelles, also confirmed the presence of “Laveran’s bodies.” In 1885, Golgi identified three distinct species of the parasite, which are now known as Plasmodium vivax, Plasmodium falciparum, and Plasmodium malariae.

Ronald Ross.

(Library of Congress)

Ronald Ross was the son of Sir Campbell Ross, a British general in the Indian Army. Born in India, the younger Ross was interested in music and the arts but entered the medical profession, following the wishes of his father. After graduation from medical school in 1879, he served as a surgeon on a series of British ships. Ross became interested in malaria following a London demonstration by Manson in the spring of 1894, at which Ross learned that parasites could be observed in the blood of patients with the disease. (Manson believed incorrectly, however, that the malarial parasite was acquired through drinking contaminated water.) Ross also became aware of Laveran’s belief that these parasites were the actual cause of the disease. Ross’s interests continued to lie, however, in the arts. During the summer of 1894, he and his wife lived with friends in Switzerland, and Ross spent the time writing two romance novels.

Returning to medicine in 1895, Ross became increasingly associated with Manson and his work in London on parasitic diseases. Manson taught techniques to Ross necessary for the observation of parasites in blood or tissue. Manson had read Laveran’s reports as early as 1889, and he became intrigued by the perceived similarities between the filarial structures and the flagella found on plasmodia. Although his ideas with respect to similarities in lifestyle between the two types of parasites were inaccurate, Manson did correctly suggest that blood cells played a role in the metamorphosis, or life-cycle changes, of these agents. Manson suggested to Ross that he continue with this work upon his return to India.

Ross returned to India in 1895. While on board ship, he began to practice dissection of cockroaches, both to develop expertise in dissection of mosquitoes and to investigate the possibility that cockroaches might carry a parasite similar to those in mosquitoes. Much of his methodology was self-taught. Ross had minimal knowledge of bacteriology, and his expertise in microscopy was primarily learned while working with Manson. He had little knowledge of the life cycle and behavior of the mosquito itself. The initial months of 1895 were spent addressing these deficits.

On August 16, 1897, while Ross was working in Secunderabad, he allowed anopheline mosquitoes to feed on a patient with malaria. On August 20, four days later, he dissected the mosquitoes and found cysts in the stomach tissue containing the malarial parasite. Similar experiments were carried out with two other species of mosquito, culex and aedes, but the results were negative. Furthermore, volunteers who drank contaminated water did not, with one exception, contract malaria.

It remained to be proven only that the infection of a healthy human with the parasite would result in that person contracting malaria. Ironically, in completing the research necessary to confirm the role of the mosquito in malarial transmission, Ross was betrayed by his mentor, Manson. The Italian physician Giovanni Grassi Grassi, Giovanni had been carrying out studies similar to those of Ross and represented Ross’s primary competition in the field. Grassi collaborated in his final experiments with Manson, even using Manson’s son as one of the subjects for the experiment. Using mosquitoes which had recently fed on a human with malaria, Grassi demonstrated that transmission of the parasite using the anopheles vector would result in the transmission of malaria as well.

Ross continued with his work, observing the life cycle of the parasite. Following the rupture of the cysts in the mosquito’s stomach, organisms migrated from the stomach to the salivary glands of the mosquito. By 1898, Ross had reported the complete life cycle of the Plasmodium parasite, as well as demonstrating that only the single species of mosquito, anopheles, was involved in its transmission. In 1902, Ross was both knighted and honored with the Nobe Nobel Prizes;physiology or medicine l Prize for his work. Laveran received a similar honor from the Nobel committee in 1907 for his discovery of the malarial parasite.

Significance

While mosquitoes had been suspected prior to this period in the transmission of certain tropical diseases, most notably malaria and yellow fever Yellow fever;and mosquitoes[Mosquitoes] , the work of Ross and others provided scientific evidence to confirm this suspicion. Furthermore, their work provided an explanation for the presence of these diseases primarily in damp, swampy areas, which were breeding grounds for the insects. In the absence of a treatment (other than quinine) or a vaccine preventive, the explanation also provided a means to address the problem: Breeding grounds for mosquitoes would need to be eliminated.

Wherever possible, swamps were drained, and standing water was treated to kill anopheline mosquitoes. The clearest result of these actions could be observed in Central America Malaria;in Central America[Central America]
Central America;malaria in : Yellow fever and malaria had ravaged U.S. soldiers during the Spanish-American War, as well as French laborers working in Panama to build a canal across the Central American isthmus. Alhough treatment of water primarily addressed yellow fever, the elimination of mosquito breeding grounds helped control malaria as well.

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