Tickborne Relapsing Fever in a Mother and Newborn Child

Editorial Note

B. hermsii is the most frequent cause of TBRF in the United States. This spirochete is transmitted to humans by the soft tick Ornithodoros hermsi, which usually is associated with the nests of chipmunks and other wild rodents.^[1] Unlike hard ticks, O. hermsi transmit spirochetes through a brief (<30 minutes' duration) and painless nocturnal bite. Humans typically are exposed to these ticks during an overnight stay in rodent-infested dwellings at elevations >2,000 feet.

After an average incubation period of 7 days (range: 2–18 days), TBRF symptoms include fever, headache, myalgias, nausea, and chills with a median duration of 3 days (range: 2–7 days) alternating with afebrile periods of a median duration of 7 days (range: 4–14 days).^[1] Febrile periods can recur ≤10 times without treatment. Moderate to severe thrombocytopenia is typical during acute TBRF illness.^[1] As occurred in the newborn's illness, spirochetes are not detected by automated blood cell counts but can be observed on direct examination of stained (Wright's or Giemsa) blood smears, with sensitivity approaching 70% during febrile episodes.^[2] Blood smears most often reveal spirochetes during acute infection and before antibiotic treatment. Alternatively, serologic testing for TBRF can be used for diagnosis but is not widely available. Antibiotics recommended for treatment include penicillin, doxycycline, and erythromycin. Patients with TBRF infection should be monitored for ≥2 hours after initial antibiotic dose for a Jarisch-Herxheimer reaction, an acute worsening of symptoms that can be life-threatening.* One case series documented such reactions among 54% of patients, demonstrating that this reaction is common.^[3]

TBRF infection can pose serious risks for mothers and neonates. Only 12 TBRF infections among pregnant women have ever been reported in the United States, including the one in this report.^{[1,3,4,5,6,7,8,9]} Among these cases, serious maternal complications of TBRF infection have been documented and include adult respiratory distress syndrome, Jarisch-Herxheimer reaction, and precipitous or premature delivery.^[4,5,6] Among newborns born to these TBRF-infected mothers, six (55%) of 11 had a documented perinatal TBRF infection; two (33%) died despite treatment.^† Potential routes of perinatal TBRF infection include transplacental transmission or acquisition during delivery; however, studies have been limited.

The findings in this report are subject to at least two limitations. First, transmission route for the newborn was not determined, but possibilities include transplacental, during birth, or during residence in the cabin. Second, the cabin remains the most likely site of exposure for the mother on the basis of arrival date and acute nature of her illness; however, no rodent nests or ticks were identified within the structure to provide more substantial evidence.

TBRF should be considered a potential diagnosis among febrile patients who reside in or have traveled to the western United States, especially those inhabiting rustic housing. Cases should be reported immediately to public health officials to facilitate identification of other potentially exposed persons and to evaluate and treat those persons for TBRF infection. Additionally, TBRF is a reportable disease in 12 western U.S. states.^§ An environmental investigation should be undertaken to search for rodent nests. Reinfection and additional TBRF illnesses can occur in housing previously linked to TBRF cases.^[10] Remediation efforts should include rodent-proofing and treatment of structures with pesticides (particularly crack- and crevice-type) by pest control specialists to reduce risk for continued tick exposure.

Morbidity and Mortality Weekly Report. 2012;61(10):174-176. © 2012  Centers for Disease Control and Prevention (CDC)