Most viral (and parasitic) infections have at least a 3 to 15 day incubation period, giving infected travelers a fairly long asymptomatic `window' in which to travel. Should a viremic visitor be bitten by a competent local vector, there is the possibility the disease may be transmitted on to others.
The State of Florida issues a weekly arbovirus report which includes imported cases of dengue and malaria, in addition to rare locally acquired cases. In their most recent report (Week 24: June 11-17, 2023) they list 23 known imported cases of malaria in 2023.
2023 International Travel-Associated Malaria Cases: Twenty-three cases of malaria with onset in 2023 have been reported. Countries of origin were: Burundi, Côte D’Ivoire, Democratic Republic of the Congo (2), Equatorial Guinea, Ghana (2), Kenya, multiple countries (4), Nicaragua (2), Nigeria (2), Pakistan, Sierra Leone (2), Sudan, and Uganda (3). Counties reporting cases were: Broward (4), Duval, Hillsborough (4), Lee, Leon (2), Miami-Dade (5), Orange, Osceola, Pinellas (3), and Sarasota. Seven cases were reported in non-Florida residents.
Imported dengue cases are even more common, with Florida reporting 88 so far in 2023. While it doesn't happen often, with enough repeated introductions, there is always a risk these diseases can become endemic.
In recent weeks, and for the first time in two decades, local transmission of malaria has been reported in two different American States (Florida & Texas). Late yesterday the CDC released a HAN Health Advisory for clinicians, public health officials, and the public on these recent cases.Which is exactly what happened a decade ago after Chikungunya began spreading on the French side of St. Martin in the Caribbean (see ECDC Epidemiological Update: Chikungunya Spreads In Caribbean and Into South America).
Locally Acquired Malaria Cases Identified in the United States
Distributed via the CDC Health Alert Network
June 26, 2023, 5:00 PM ET
CDCHAN-00494
Summary
The Centers for Disease Control and Prevention (CDC) is issuing this Health Alert Network (HAN) Health Advisory to share information and notify clinicians, public health authorities, and the public about—
- Identification of locally acquired malaria cases (P. vivax) in two U.S. states (Florida [4] and Texas [1]) within the last 2 months,
- Concern for a potential rise in imported malaria cases associated with increased international travel in summer 2023, and
- Need to plan for rapid access to IV artesunate, which is the first-line treatment for severe malaria in the United States.
Background
CDC is collaborating with two U.S. state health departments with ongoing investigations of locally acquired mosquito-transmitted Plasmodium vivax malaria cases. There is no evidence to suggest the cases in the two states (Florida and Texas) are related. In Florida, four cases within close geographic proximity have been identified, and active surveillance for additional cases is ongoing. Mosquito surveillance and control measures have been implemented in the affected area. In Texas, one case has been identified, and surveillance for additional cases, as well as mosquito surveillance and control, are ongoing. All patients have received treatment and are improving.Locally acquired mosquito-borne malaria has not occurred in the United States since 2003 when eight cases of locally acquired P. vivax malaria were identified in Palm Beach County, FL (1). Despite these cases, the risk of locally acquired malaria remains extremely low in the United States. However, Anopheles mosquito vectors, found throughout many regions of the country, are capable of transmitting malaria if they feed on a malaria-infected person (2). The risk is higher in areas where local climatic conditions allow the Anopheles mosquito to survive during most of or the entire year and where travelers from malaria-endemic areas are found.In addition to routinely considering malaria as a cause of febrile illness among patients with a history of international travel to areas where malaria is transmitted, clinicians should consider a malaria diagnosis in any person with a fever of unknown origin regardless of their travel history. Clinicians practicing in areas of the United States where locally acquired malaria cases have occurred should follow guidance from their state and local health departments. 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.
Malaria is a serious and potentially fatal disease transmitted through the bite of an infective female anopheline mosquito. Though rare, malaria can also be transmitted congenitally from mother to fetus or to the neonate at birth, through blood transfusion or organ transplantation, or through unsafe needle-sharing practices. Malaria is caused by any of five species of protozoan parasite of the genus Plasmodium: P. falciparum, P. vivax, P. malariae, P. ovale, and P. knowlesi. Worldwide, more than 240 million cases of malaria occur each year (95% in Africa).
Almost all cases of malaria in the United States are imported and occur in people traveling from countries with malaria transmission, many from sub-Saharan Africa and South Asia. Before the COVID-19 pandemic, approximately 2,000 cases of mostly travel-related malaria were diagnosed in the United States each year; approximately 300 people experienced severe disease (most P. falciparum), and 5 to 10 people with malaria died yearly (3). Most imported cases of malaria in the United States are diagnosed during summer and early fall. In 2023, CDC expects summer international travel among U.S. residents will be increasing to pre-COVID-19 pandemic levels (4).
Over the past 25 years we've seen CCHF (Crimean-Congo Hemorrhagic Fever) introduced to Western Europe, both Zika and Chikungunya arrive in the Americas, Dengue's return to Florida after 70 years, and the arrival (in 1999) and subsequent spread of West Nile Virus across much of North America.
Add in climate change, and the expanding geographic range of competent vectors (see ECDC invasive mosquito maps), and places previously thought immune to these types of epidemics are increasingly at risk.
As we've discussed previously (see EID Journal: Hx of Mosquitoborne Diseases In the U.S. & Implications For The Future), the United States has a long history of enduring mosquito-borne epidemics, which were largely eliminated in the 20th century by extensive mosquito control efforts.
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| Outbreaks of yellow fever reported during 1693–1905 among cities comprising part of present-day United States. - Credit EID Journal |
While a remarkable achievement, there are increasing reports of the spread of insecticide resistant mosquitoes (see Science Advances: A Widespread Super–Insecticide-Resistant Aedes aegypti Mosquito in Asia) that threaten to degrade mosquito control efforts in the future.
All reasons why the advice offered to the public in today's HAN advisory (see below) makes sense every summer.
In addition to old threats like malaria, new vector borne pathogens continue to emerge (see Virulence: Langya henipavirus - Is it a potential cause for public health concern?), and there are likely many more out there yet to be identified.
- Take steps to prevent mosquito bites and control mosquitos at home to protect yourself from any mosquito-borne illness.
- Before you travel, learn about the health risks and precautions for malaria and other diseases for your destination.
- If you are traveling internationally to an area where malaria occurs, talk to your healthcare provider about medicines to prevent you from getting malaria.
- 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.
For more on some of these emerging disease threats, you may wish to revisit:
