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Saving Lives, Buying Time: Economics of Malaria Drugs in an Age of Resistance
parasites were growing in the mosquito, he published his observations (“On some peculiar pigmented cells found in two mosquitoes fed on malarial blood”) in the British Medical Journal in December 1897.
After transferring to Calcutta, Ross designed experiments involving Plasmodium relictum, the malaria parasite of sparrows and crows. Ross identified sporozoites in the salivary glands of mosquitoes that had previously fed on malarious birds. He subsequently infected 21 of 28 fresh sparrows through these mosquitoes (Sherman, 1998). He communicated all of his findings to Patrick Manson who shared them at a meeting of the British Medical Association at the University of Edinburgh in July 1898 (Harrison, 1978). In 1902, Ross received the Nobel Prize for discovering the mosquito stages of malaria.
Ross was not the only investigator who demonstrated the malaria life cycle in the mosquito, however. Credit for confirming that human malaria parasites pass through the same developmental stages in the mosquito as the avian parasites observed by Ross belongs to a group of Italian scientists—in particular, Giovanni Battista Grassi (1854-1925), Amico Bignami, Giovanni Bastianelli, Antonio Dionisi, and Angelo Celli. Following Ross’s publication, Grassi (an expert in mosquito taxonomy) not only identified Anopheles maculipennis as the vector of human disease in the marshy Roman Campagna, but transmitted the malaria parasite Plasmodium vivax to a healthy human volunteer. Because each claimed credit for discovering malaria’s life cycle in the mosquito, Grassi and Ross were bitter toward each other for the remainder of their careers.
Parenthetically, Ronald Ross owed much of his success to his teacher and mentor Sir Patrick Manson, considered by many the father of tropical medicine. While working in Amoy and Formosa, Manson was the first researcher to discover that mosquitoes siphon first-stage microfilariae from the bloodstreams of patients with the parasitic disease, filariasis. However, Manson never imagined the final step in the filarial life cycle; namely, that infected mosquitoes might inoculate third-stage filaria larvae back into humans through a subsequent bite. It was left to his protégé Ross to discover that parasites can travel two ways through the proboscis of a mosquito.
Discovering the Parasite in Human Tissue
The third piece of the human malaria puzzle—where sporozoites inoculated by mosquitoes undergo early development in the human host—was solved in 1948. Although previous researchers had found that bird malaria initially reproduced in tissues of the lymph system and the bone marrow, the sanctuary for primate and human malaria outside of red blood cells remained a mystery. Then H. E. Shortt, P. C. C. Garnham, and colleagues