Locally acquired malaria in Europe and the US

In June 2023, concerning news of locally acquired malaria was reported in the US – the first such cases in twenty years. At the time, there were fears that these could be the first signs in an outbreak. Nearly two months on, what important issues did these cases highlight?

As more countries are eliminating malaria, their concerns turn towards surveillance and stopping malaria from coming back. In the cases of countries and regions that have been ‘malaria free’ for decades,  there is a relatively small number of cases of malaria each year, and these are usually attributed to the patient having traveled to endemic regions. For instance, the ECDC’s Malaria- Annual Epidemiological Report for 2021 attributed 99.7% of malaria cases in the EU to the patient having traveled to endemic regions. The peak of these cases occur during and just after the summer holidays.

However, there were thirteen cases of malaria in 2021 that were confirmed to have been acquired in the EU. Four of these cases were reported in Greece – three in the Attica region were caused by Plasmodium falciparum and one in Thessaloniki caused by Plasmodium vivax. The mode of transmission could not be identified in these cases, although blood transfusion was ruled out. There were nine cases reported in France, eight of which were attributed to P. falciparum (four of these were hospital acquired, two were airport-related and two remain unknown). There was one case of Plasmodium ovale malaria in France, and this is thought to have been a case of recurring malaria.

In June 2023, news headlines were filled with alarm over five cases of locally acquired malaria in the USA. The reason for such media attention? Peter McElroy, PhD, Chief, Malaria Branch, Division of Parasitic Diseases and Malaria states: Cases of locally transmitted malaria in the United States have been rare. The last documented locally acquired, mosquito-transmitted case of Plasmodium vivax malaria occurred in Palm Beach County, Florida, in July-August 2003.”

Initially, there were concerns in the news media about what these cases could potentially indicate, and there have now been further reported cases, such the case reported in Maryland last week. These cases highlight the need for continued surveillance and prompt diagnosis and treatment – to prevent sporadic cases becoming outbreaks. Dr McElroy agrees on this last point, stating, The risk of contracting malaria in the U.S. remains very low. However, the detection of locally acquired malaria underscores:

  • The continued potential for local transmission
  • The need for surveillance to detect malaria in the U.S. and monitor trends 
  • The importance of prompt diagnosis and treatment assistance to clinicians who may encounter patients with possible or confirmed malaria infection but are unfamiliar with it

…Prompt diagnosis and treatment of people with malaria can prevent progression to severe disease or death and limit ongoing transmission to local Anopheles mosquitos. Individuals can take steps to prevent mosquito bites and control mosquitos at home to prevent malaria and other mosquito-borne illnesses.”

There have now been nine reported cases of locally acquired malaria (seven in Florida, one in Texas and one in Maryland).  Interestingly, eight of the cases are reported to be caused by P.vivax but the Maryland case is P. falciparum.  This is very different to what is seen in the US from imported/ travel related malaria – about 70% of imported malaria in the US is caused by P.falciparum and only 10% by P. vivax.

Not many people realise that the CDC was actually created in 1949 to help tackle malaria in the United States, because the disease was a major threat in the country. According to Dr McElroy, it still works to tackle malaria on a day-to-day basis and support state and local health departments to investigate cases like the ones in May – August. A breakdown on the day to day work done by the CDC and how it supports during cases of malaria outbreaks – source CDC).

Day-to- Day work:

      • Administers the National Malaria Surveillance System
      • Collaborates with health departments and other partners to investigate unusual cases of malaria diagnosed in the U.S.
      • Provides recommendations to U.S. residents and clinicians for malaria prevention and treatment
      • Consults with clinicians to provide advice on the diagnosis and treatment of malaria in the United States
      • Provides testing services on blood samples for malaria and technical assistance to laboratories

How the CDC supports during potential outbreaks:

      • Provides laboratory support to confirm suspected malaria cases, including species confirmation
      • Assists with case investigations to identify specific risk factors for malaria
      • Advises on strategies to pursue active case detection in affected communities
      • Recommends approaches for trapping Anopheles mosquitoes in areas where malaria patients reside
      • Performs tests on captured Anopheles mosquitoes to determine presence of malaria parasites in resident mosquitoes


Some of the reporting of the US cases seemed to imply climate change as the driver, but as Dr McElroy states: “Though we know in general that climate can be one of many factors that can impact vector-borne diseases, in this situation, there is no compelling reason to think it is the cause of these sporadic cases.”

Even so, climate change has resulted in mosquito populations (that spread malaria or other vector-borne disease) spreading further into the US and Europe, where they were not present before (or for a long time). In fact, just the other day, an Aedes mosquito flew right past me as I was sitting watching television in my home in west London – not something I thought I would ever see!

It is therefore important for the public – whether they live in endemic areas or not – to be mindful of the risks of malaria and other vector-borne diseases AND importantly, learn to change our own behaviors to reduce the risks. The CDC recommends the below actions in the case of malaria, but much of it can be applied to other vector-borne diseases:

Recommendations for the public 

    • Take steps to prevent mosquito bites and control mosquitos at home to protect yourself from any mosquito-borne illness.
    • Use Environmental Protection Agency (EPA)-registered insect repellents with one of the active ingredients below.
      • DEET
      • Picaridin (known as KBR 3023 and icaridin outside the US)
      • IR3535
      • Oil of lemon eucalyptus (OLE)
      • Para-menthane-diol (PMD)
      • 2-undecanon
    • Wear loose-fitting, long-sleeved shirts and pants
    • Use 0.5% permethrin to treat clothing and gear (such as boots, pants, socks, and tents) or buy permethrin-treated clothing and gear. – Do not use permethrin products directly on skin.
    • Keep windows and doors closed or covered with screens to keep mosquitoes out of your house. Repair broken screening on windows, doors, porches, and patios.
    • Empty standing water at least once a week to prevent mosquitos from laying eggs.
    • Before you travel, learn about the health risks and precautions for malaria and other diseases for your destination.
    • If you are traveling to an area where malaria occurs, talk to your healthcare provider about malaria prevention medication.
    • If you have traveled to an area where malaria occurs and develop fever, chills, headache, body aches, and fatigue, seek urgent medical care and tell your healthcare provider that you have traveled.

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