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An outbreak of introduced malaria in California possibly involving secondary transmission
Abstract:
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.
Insights
In 1974, California reported 12 Plasmodium vivax malaria cases, with local mosquito transmission likely. This outbreak highlights the risk of introduced malaria and the importance of surveillance.
Area of Science:
- Medical Entomology
- Infectious Diseases
- Epidemiology
Background:
- Malaria transmission in non-endemic regions poses public health challenges.
- Introduced malaria outbreaks in the US are infrequent but significant.
- California had not reported malaria cases since 1957.
Purpose of the Study:
- To report and analyze a 1974 Plasmodium vivax malaria outbreak in California's Sacramento Valley.
- To investigate the source and transmission dynamics of the introduced malaria cases.
- To assess the impact of surveillance on case detection.
Main Methods:
- Case reporting and epidemiological investigation of Plasmodium vivax malaria.
- Environmental surveillance focusing on Anopheles freeborni mosquito populations.
- House-to-house case-finding surveys in a defined transmission area.
Main Results:
- Twelve cases of Plasmodium vivax malaria were identified, with at least three resulting from local mosquito transmission.
- The outbreak involved Punjabi immigrants and an American visitor, linked to malaria resurgence in India.
- High Anopheles freeborni populations coincided with local transmission; surveillance did not detect new cases but potentially improved awareness.
Conclusions:
- The 1974 outbreak represents the first California malaria case since 1957 and the 11th in the US since 1952.
- Local transmission was likely facilitated by Anopheles freeborni and imported cases from Punjab, India.
- Enhanced surveillance may improve the detection of future introduced malaria cases.