A recent study published in Emerging Infectious Diseases discusses a case report of the probable vertical transmission of tick-borne encephalitis virus (TBEV) from an unvaccinated mother to her newborn via breast milk.

TBEV is usually transmitted by tick bites or by the consumption of raw milk of infected sheep, cows, and goats. The mother-to-newborn TBEV transmission through breastfeeding has neither been confirmed nor ruled out.

The case report

In the present work, the researchers reported a case of TBEV transmission through breast milk from an unvaccinated mother to her newborn.

In May 2020, a female aged 29 years complained of temporal headaches, neck stiffness, muscular weakness, and fever (body temperature 38.5°C) that persisted for three to four days. On May 29^th, 2020, she was hospitalized at an emergency care health facility. On admission, she reported transient fever a week prior to the hospitalization that persisted for many days. Based on the clinical findings, she was diagnosed with a neuro-infection.

The patient developed paresthesia and paresis in the left and right hands, respectively. A day after the hospital admission, she developed generalized seizures and a stupor, and her oxygen saturation dropped to 80%. She had developed TBEV immunoglobulin M (IgM) antibodies in her cerebrospinal fluid (CSF) and serum.

Before hospital admission, she was breastfeeding her eight-month-old newborn, which included when she developed clinical manifestations. On May 31^st, 2020, she was admitted to the intensive care unit (ICU). Her newborn was hospitalized in an in-patient care unit due to fever (body temperature at or less than 40°C) for a day before the hospitalization.

However, the newborn did not develop clinical signs of irritation of the meninges, and CSF did not demonstrate any TBEV IgM antibodies. Thus, the newborn received hospital discharge and was subsequently put on a home-care regimen on June 4^th, 2020. No tests such as reverse transcription-polymerase chain reaction (RT-PCR) were carried out to detect TBEV ribonucleic acid (RNA).

During the post-discharge period, the newborn’s body temperature escalated to 38°C. Subsequently, on June 11^th, 2020, the newborn was assessed at an emergency care facility due to apathy and low-grade fever. However, the newborn was not hospitalized in any in-patient care facility and was subsequently discharged since the clinical condition of the newborn was considered to represent the effects of teething and not any critical illness. However, on June 25^th, 2020, a serum sample of the newborn was obtained at a pediatrician’s office and evaluated for TBEV IgM antibodies, for which the newborn had tested positive.

The mother resided in a disease-endemic area of ​Slovakia, where the highest number of TBE had been reported. Her husband reported that she consumed dairy products from an animal farm and had a tick-bite history one month prior to her hospital admission. She had also not received a TBE vaccination.

Discussion

TBE cases in newborns have not been reported frequently. However, the increased number of cases reported recently from many European countries indicates that TBE is probably underreported and is not extremely rare in newborns. Some of the cases do not have a tick-bite history, indicative of a different route of TBEV transmission.

Breast milk could be a potential route of TBEV transmission from the mother to her newborn as alimentary tract infections have been reported in humans to be caused by consuming unpasteurized milk of infected animals. The mother-to-newborn transmission by breast milk has also been reported in experimental models for the Zika virus, which belongs to the same Flaviviridae family as TBEV. Further, TBEV is usually present in the blood and milk of virus-infected ungulate animals for one to five days and two to eight days, respectively.  

However, to date, there has been no conclusive evidence on breast milk as a potential route of viral transmission in humans. A previous case report suggested that viral transmission occurs through breastfeeding in a serologically confirmed-TBEV-positive mother and her 10-days-old breastfed infant in Lithuania.

The incubation period of TBEV is typically seven to 14 days and three to four days for tick-borne infections and alimentary tract infections, respectively. The present case report findings are in accordance with these previously reported findings.

TBE vaccination has shown 99% efficacy and has been reported to provide short-term immune protection to infants via transplacental antibody transfer from their vaccinated mothers. Since child vaccination has been recommended for children ≥1 year, only non-pharmaceutical strategies can be implemented for TBE prevention in newborns.

Conclusion

Based on the present case report findings, mother-to-newborn TBEV transmission could occur via breast milk from unvaccinated mothers to their newborns. Further studies must be conducted to validate this finding, which can have profound implications for breastfeeding management by unvaccinated mothers with tick-bite history who reside in regions endemic to TBEV.

Written by

Pooja Toshniwal Paharia

Dr. based clinical-radiological diagnosis and management of oral lesions and conditions and associated maxillofacial disorders.