New study reveals emerging cases of babesiosis in Mid-Atlantic region

Annapolis, MD; April 29, 2025—A newly published study in the Journal of Medical Entomology provides critical insights into the emergence of babesiosis in the Mid-Atlantic region, documenting human cases and the presence of Babesia microti in local tick populations.

The article, titled "Emerging Babesiosis in the Mid-Atlantic: Autochthonous Human Babesiosis Cases and Babesia microti (Piroplasmida: Babesiidae) in Ixodes scapularis (Acari: Ixodidae) and Ixodes keiransi (Acari: Ixodidae) Ticks from Delaware, Maryland, Virginia, West Virginia, and the District of Columbia, 2009-2024," presents a comprehensive analysis of the growing public health threat posed by this tick-borne disease.

The study confirms that babesiosis, historically concentrated in the Northeast and Upper Midwest, is now expanding in the Mid-Atlantic region. The research highlights an increasing number of locally acquired (autochthonous) human cases and the detection of Babesia microti, the primary causative agent of human babesiosis, in blacklegged ticks (Ixodes scapularis) and Ixodes keiransi ticks. The study was conducted by Ellen Stromdahl, Ph.D., retired entomologist at the Vector-Borne Disease Laboratory, Defense Centers for Public Health-Aberdeen, along with 21 colleagues from the Maryland Department of Health, Delaware Department of Natural Resources and Environmental Control, Old Dominion University, Delaware Technical Community College, Virginia Department of Health, University of Richmond, DC Health, U.S. Centers for Disease Control and Prevention, U.S. Food & Drug Administration, West Virginia Department of Health, and Mayo Clinic.

Key findings include:

• Autochthonous human babesiosis cases were reported for the first time from the Mid-Atlantic U.S. jurisdictions of Maryland, Virginia, West Virginia, and the District of Columbia between 2009 and 2024.
• Babesia microti was detected in ticks collected from Delaware, Maryland, Virginia, West Virginia, and DC.
• The study provides the first report of Ixodes keiransi as a potential vector of Babesia microti.
• The data suggest that babesiosis is becoming a growing concern in areas where it was previously considered rare or absent.

"The findings underscore the need for increased surveillance, public awareness, and preventive measures against tick-borne diseases in the Mid-Atlantic region," says Stromdahl. "Healthcare providers should consider babesiosis in the differential diagnosis for patients with febrile illness, particularly during peak tick-activity seasons."

Babesiosis, caused by microscopic parasites that infect red blood cells, can range from asymptomatic to severe illness, particularly in immunocompromised individuals. Babesiosis can be severe in the elderly or immunocompromised, especially when patients have concurrent infections with Borrelia burgdorferi (the bacteria that causes Lyme disease). Diagnosis can be difficult, as the disease is rare, and early symptoms of babesiosis resemble conditions more likely to be expected in elderly populations or associated with other more common tick-borne diseases. As a result, babesiosis might be misdiagnosed or treated empirically with antibiotics typically prescribed for Lyme disease or anaplasmosis, such as doxycycline. However, antibiotics alone are not effective against babesiosis, making early and accurate diagnosis crucial.

Additionally, coinfection of Ixodes scapularis with B. microti and B. burgdorferi is common. In this study, half of the ticks positive for B. microti were also infected with B. burgdorferi, and one was triple-infected with Anaplasma phagocytophilum, B. burgdorferi, and B. microti. Further, additional I. scapularis from Maryland and Virginia were found concurrently infected with A. phagocytophilum, B. burgdorferi, B. microti, and Borrelia miyamotoi. Practitioners need to be alert to concurrent infections that might complicate diagnosis and treatment.

This research emphasizes the importance of enhanced public health surveillance, including conducting thorough investigations of all potential human cases of babesiosis and conducting tick surveillance whenever possible.

Education about this emerging risk, including how to prevent infection in the first place, how to recognize infection, and appropriate treatment, should be increased for medical providers, public health practitioners and the general population.

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"Emerging Babesiosis in the Mid-Atlantic: Autochthonous Human Babesiosis Cases and Babesia microti (Piroplasmida: Babesiidae) in Ixodes scapularis (Acari: Ixodidae) and Ixodes keiransi (Acari: Ixodidae) Ticks from Delaware, Maryland, Virginia, West Virginia, and the District of Columbia, 2009-2024," was published online on April 22, 2025, in the Journal of Medical Entomology. Journalists may request access to the full article via the contact below.

CONTACT:

• Ellen Stromdahl (retired), Vector-Borne Disease Laboratory, Defense Centers for Public Health-Aberdeen, 410-598-0662, ellen.stromdahl@gmail.com
• Joe Rominiecki, Entomological Society of America, jrominiecki@entsoc.org, 301-731-4535 x3009

ABOUT:

The Vector-Borne Disease Laboratory (VBDL) is a specialized division within Defense Centers for Public Health–Aberdeen (DCPH-A) that focuses on researching, monitoring, and mitigating vector-borne diseases affecting military personnel. It supports the Department of Defense (DOD) Military Tick Identification/Infection Confirmation Kit (MilTICK) by using molecular methods (PCR) to identify vectors and assessing their disease-carrying potential, and it maintains databases on vector distribution and pathogen prevalence.

ESA is the largest organization in the world serving the professional and scientific needs of entomologists and people in related disciplines. Founded in 1889, ESA today has nearly 7,000 members affiliated with educational institutions, health agencies, private industry, and government. Headquartered in Annapolis, Maryland, the Society stands ready as a non-partisan scientific and educational resource for all insect-related topics. For more information, visit www.entsoc.org.

The Journal of Medical Entomology publishes research related to all aspects of medical entomology and medical acarology, including the systematics and biology of insects, acarines, and other arthropods of public health and veterinary significance.For more information, visit https://academic.oup.com/jme, or visit www.insectscience.org to view the full portfolio of ESA journals and publications.