Health officials in Sarasota County, Florida, confirmed two cases of locally transmitted malaria in late May and mid-June, respectively. Later, on June 23, Texas announced a confirmed case in Cameron County. This is significant as the United States has not reported locally acquired malaria in the past two decades.
Typically, the approximately 2,000 annual malaria cases in the US are linked to travel outside the country. However, in these recent cases, neither the individuals in Florida nor the one in Texas had traveled, indicating local transmission. While experts urge caution and emphasize that these cases do not suggest widespread transmission, the incidents raise concerns about potential further spread.
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Mosquitoes can infect multiple individuals before an outbreak is identified, underscoring the possibility of more undetected cases. The recent cases are considered highly unusual given that the US last documented a local transmission in 2003.
These cases serve as a reminder that malaria could make a comeback in the US, necessitating preparedness and vigilance in the public health infrastructure. With changing climate patterns and mosquito migration, malaria may find new areas to settle where it hasn't been prevalent before, highlighting the need for proactive measures.
The recent cases of locally transmitted malaria in Florida and Texas have been identified as Plasmodium vivax, a less severe form of the disease compared to P. falciparum. The latter is 10 times more deadly than the form as per a 2014 paper published in the Open Forum Infectious Diseases.
While P. vivax is not as deadly, Vox reported that it can still lead to life-threatening complications, such as brain swelling, lung congestion, and kidney failure. Symptoms of the infection include recurrent fevers and a wide range of flu-like or liver disease-like symptoms.
What makes P. vivax particularly challenging is its ability to lie dormant in the liver for extended periods, causing the infection to resurface long after the initial exposure. Although most vivax malaria cases occur in East Africa, South Asia, and northern South America, these recent cases in the US raise concerns about its potential spread.
Malaria was previously a significant problem in the US until it was successfully eliminated in the 1950s through measures like DDT insecticide spraying. Furthermore, the preference of malaria-transmitting mosquitoes to bite at night, coupled with improved household protection such as window screens and air conditioning, has contributed to keeping malaria at bay in the country.
However, under specific circumstances, malaria transmission can still occur in the US, highlighting the need for ongoing vigilance and preventive measures.
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Malaria Transmission in the US
Understanding how malaria spreads is crucial in exploring local transmission of malaria. Malaria is transmitted when an infected person is bitten by a female Anopheles mosquito, which then bites an uninfected person about a week later.
During this time, the mosquito resides in stagnant warm water with vegetation growth along the banks. It prefers natural habitats like forests rather than water puddles near human habitation.
For local transmission to occur, the Centers for Disease Control and Prevent (CDC) says that a person who acquired P. vivax malaria overseas must come into proximity with the habitat of Anopheles mosquitoes to be bitten.
The mosquito then incubates the infection for a few days before being capable of infecting another person. When it bites the next individual, particles in its saliva mix with the person's blood, resulting in the transmission of the disease. The mosquito can continue to feed on other people and potentially infect them even after a few weeks.
Understanding the essential elements of malaria transmission, such as infected travelers, mosquitoes, uninfected individuals, and the environment, is crucial for comprehending the current situation and mitigating the risk of further local spread.
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