Update on Locally Acquired Malaria in the United States - July 12th, 2023

About 2,000 cases of malaria are diagnosed in the United States each year. however these are linked to international travel. For the first time since 2003 locally acquired cases of malaria has been diagnosed in Florida and Texas. Malaria spread, even with the current outbreak is exceedingly rare in the United States. On June 26th, 2023 the Florida Department of Health issued a mosquito born illness advisory for the entire state. This health advisory provides helpful information regarding mosquito control around the home and can be read here.

All 6 malaria cases in Florida are believed to have been acquired in Sarasota County. In Texas one case was detected in Cameron County. It is reported that all patients diagnosed with malaria are receiving treatment and improving.

About 80 types of mosquitos are found in Florida with 14-16 (depending on the publication) species being Anopheles mosquitos that are capable of transmitting malaria. Transmission of malaria within the United States is very rare and public health officials are working to ensure vector control (mosquito control) is increased in areas where positive cases have been detected. Sentinel chichens are used by local health departments around the world (United States, Australia, India, and Italy are just a few examples) in places where mosquito born illness is common. The chickens serve as an early detection system for local increases in mosquito born illness. More can be read about how sentinel chickens are used to detect and track the spread of mosquito born illness here: Movement of St. Louis encephalitis virus in the Western United States, 2014- 2018 and West Nile virus surveillance using sentinel birds.

Vector control around the home including emptying containers of standing water can help reduce the spread of mosquito born illness. Using mosquito repellent, avoiding being outside while mosquitos are most active (around sunrise and sunset), and wearing loose fitting clothing can help reduce the chance of being bitten. Mosquitos in the United States can also carry West Nile virus (36 documented cases across 10 states in the US in 2023), and up until 2016-17 spread Zika virus with the last locally acquired cases in Florida and Texas (https://www.cdc.gov/zika/geo/index.html)

Malaria symptoms start like the flu and include fever, chills, headaches, muscle aches, abdominal pain, fatigue and nausea. If you suspect that you are infected it is advised that you immediately contact your local health provider. Untreated severe malaria infection is nearly always fatal, but if treated mortality is about 2% (Malaria, K. Walter et al. JAMA Patient Page, 2022).

It is estimated there are 241 million malaria cases world wide resulting in over 600,000 deaths annually. In 2021 (yes I posted about this on TikTok then!) the World Health Organization recommended the first malaria vaccine, RTS,S for children in sub-Saharan Africa. This vaccine reduces childhood death from malaria by 30%, it is the first malaria vaccine to show any level of useful efficacy. The vaccine is not available to adults.

What to do if you live in or near an area where Malaria has been detected:

CDC Recommendations for the Public:

Recommendations for the Public

• Take steps to prevent mosquito bites and control mosquitos at home to protect yourself from any mosquito-borne illness.

• If you have traveled to an area where malaria occurs and develop fever, chills, headache, body aches, and fatigue, seek medical care and tell your healthcare provider that you have traveled.

The full summary can be found here: https://emergency.cdc.gov/han/2023/han00494.asp

More from the CDC on malaria can be found here: Malaria Frequently Asked Questions (FAQs).

My current opinion is that we are unlikely to see continued sustained malaria detection this year. There may be a handful of other cases, possibly even in other states where mosquitos are active. I’d expect if not in Texas or Florida these states would be nearby. Mosquitos don’t have significant range with the maximum travel distance being an estimated 7 miles from their breeding grounds (most only travel about 3 miles: reference). Travel of an infected person who is then again bit would be the likely source of a new outbreak.

Of note, there are four kinds of malaria parasites that infect humans, the one found in Florida and Texas is Plasmodium vivax or P. vivax which is generally considered less dangerous than Plasmodium falciparum which most often causes severe illness and death. P. vivax is spread only by mosquito to human to mosquito bites and is not known to be zoonotic (it only infects people and can not be transmitted to or spread by pets or wild birds). In summary, I don’t believe we have much to worry about with this one. It is an ongoing situation being closely monitored.

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