Many people may not know that there was a time, not long ago, when malaria was more than a disease you only worried about when traveling. Malaria is a mosquito-borne disease resulting from a parasite that causes fever, chills and flu-like symptoms that can progress to liver and kidney failure, or even coma and death in the worst cases. There are four protozoa that can cause the disease: Plasmodium falciparum, P. malariae, P. ovale and P. vivax. All four of these parasites are carried by mosquitoes in the genus Anopheles. Anopheles quadrimaculus is the most important vector east of the Rocky Mountains, while An. freeborni, An. hermsi, and An. punctipennis have been implicated in transmission in California. The story of malaria in California focuses mostly on one of the most significant of the malaria parasites: Plasmodium vivax, “the one that hides.”
It is believed that P. vivax was first introduced to North America in the late 1400’s and early 1500’s by settlers arriving from Europe. Malaria was brought into California in the early 1830’s by fur trappers from the Hudson’s Bay Company. Vivax malaria quickly became endemic in California, where it was rampant throughout the gold rush and was considered to be a contributing factor to the loss of many native American tribes. In the early 1900’s, malaria was recognized as a mosquito-borne disease. The Mosquito Abatement Act of 1915 coupled with the establishment of many organized mosquito control districts facilitated the steady decline of cases in California.
By the 1950’s Plasmodium vivax was no longer considered endemic in California, but there were still significant cases of locally acquired malaria every year boosted by the travel and movement of troops during the Korean War. In 1955 the 8th World Health Assembly launched the Global Malaria Eradication Campaign. The goal was to eliminate malaria from the world using a combination of indoor and outdoor pesticide applications, personal protection, and habitat modification, helmed by vector control agencies in every country. From a high of 2,707 cases (32 acquired locally) in California in 1953, the number dropped swiftly to 108 cases (6 acquired locally) in 1957 (Sutter, Colusa, and San Diego Counties), to 61 (1 local) in 1958 (Sacramento County), and then 40 (0 local) in 1960. By 1978, 37 of the 143 countries that joined the Campaign were malaria-free, including the United States.
While Vector Control no longer employs “scorched earth” techniques, we still believe in the importance of mosquito control as a way to prevent the spread of diseases. Every traveler returning from a malaria endemic region could potentially reintroduce diseases like malaria or dengue to a waiting population of mosquitoes. As the potential malaria vectors Anopheles hermsi, An. freeborni and An. punctipennis are present in the Coastal Region of California, the District laboratory is in the planning stages of a project to improve our knowledge of the distribution of these species. This knowledge will help us develop better targeted approaches to travel-related introductions of malaria in order to prevent it from ever establishing again.
If you would like to learn more about the history of Malaria in the United States, we recommend the book “Malaria: Poverty, Race, and the Public Health in the United States” by Margaret Humphreys. Published in 2001 by John Hopkins University Press, Baltimore, MD.