Case of probable transmission of tick-borne encephalitis virus from an unvaccinated mother to a child through breastfeeding


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

Study: Breast milk as a transmission route of tick-borne encephalitis virus from mother to child. Image Credit: nechaevkon/Shutterstock

TBEV is usually transmitted by tick bites or by consuming raw milk from infected sheep, cows and goats. Transmission of TBEV from mother to neonate through breastfeeding has neither been confirmed nor ruled out.

The case report

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

In May 2020, a 29-year-old woman complained of temporal headache, stiff neck, muscle weakness and fever (body temperature 38.5°C) lasting for three to four days. May 29and, 2020, she was hospitalized in an urgent care facility. On admission, she reported a transient fever a week prior to hospitalization which persisted for several days. Based on the clinical findings, he was diagnosed with a neuro-infection.

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

Prior to her admission to hospital, she was breastfeeding her eight-month-old newborn, when she developed clinical manifestations. May 31st, 2020, she was admitted to the Intensive Care Unit (ICU). Her newborn was admitted to an inpatient care unit with fever (body temperature 40°C or less) for one day prior to admission.

However, the neonate did not develop clinical signs of meningeal irritation and CSF did not show anti-TBEV IgM antibodies. Thus, the newborn was discharged from hospital and was subsequently placed on home care on June 4.and2020. No tests such as reverse transcription-polymerase chain reaction (RT-PCR) have been performed to detect TBEV ribonucleic acid (RNA).

During the post-discharge period, the newborn’s body temperature rose to 38°C. Then on June 11and, 2020, newborn was assessed in an urgent care facility for listlessness and mild fever. However, the newborn was not hospitalized in any inpatient care facility and was later discharged since the newborn’s clinical condition was considered to represent the effects of teething and not serious illness. However, on June 25and2020, a serum sample from the newborn was obtained from a pediatrician’s office and evaluated for TBEV IgM antibodies, for which the newborn had tested positive.

The mother resided in an endemic area of ​​Slovakia, where the highest number of TBEs had been reported. Her husband said she had consumed dairy products from a cattle farm and had a history of tick bites a month before she was admitted to hospital. She also had not received a TBE vaccine.


Cases of TBE in neonates have not been reported frequently. However, the increase in the number of cases reported recently in many European countries indicates that TBE is probably underreported and not extremely rare in neonates. Some of the cases have no history of a tick bite, indicating a different route of TBEV transmission.

Breast milk could be a potential route of transmission of TBEV from mother to her neonate, as infections of the digestive tract in humans have been reported to be caused by consumption of unpasteurized milk from infected animals. Mother-to-newborn transmission through breast milk has also been reported in experimental models for Zika virus, which belongs to the same Flaviviridae family as TBEV.. Additionally, TBEV is typically 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 is no conclusive evidence on breast milk as a potential route of viral transmission in humans. A previous case report suggested that viral transmission occurred through breastfeeding in a serologically confirmed TBEV-positive mother and her breastfed 10-day-old infant in Lithuania.

The incubation period for TBEV is typically seven to 14 days and three to four days for tick-borne infections and digestive tract infections, respectively. The findings of this case report are consistent 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 transfer of antibodies from their vaccinated mothers. Since childhood vaccination has been recommended for children ≥ 1 year of age, only nonpharmaceutical strategies can be implemented for the prevention of TEE in neonates.


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


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