A doctor and a nurse who treated one of the two nurses infected with the Nipah virus were admitted to the Infectious Diseases and Beliaghata General Hospital on Tuesday evening after developing mild symptoms, including fever and cough.

Health department officials said there are several theories about how the two nurses contracted the virus. One is that they had treated a patient with similar symptoms at a private hospital in Barasat, who later died without a confirmed diagnosis.

State health authorities said the doctor and nurse admitted to the ID hospital are stable. Their samples have been sent for testing. Tuesday’s admissions mark the first instance of anyone exposed to the confirmed Nipah patients being hospitalised. Meanwhile, the condition of the two nurses at the Barasat hospital remains critical.

The state government had confirmed on Tuesday that the nurses, employed at the same Barasat hospital, tested positive for the virus in confirmatory tests at the National Institute of Virology (NIV), Pune.

“As the doctor and nurse admitted at the ID hospital were exposed to one of the infected patients and showed symptoms that overlap with Nipah virus infection, we decided to admit them for observation,” said a health official.

Doctors said Nipah infection symptoms include high fever, headache, muscle pain, vomiting and sore throat, followed by dizziness, drowsiness, altered consciousness and neurological symptoms.

The doctor and nurse at the ID hospital had provided care to one of the infected nurses when the patient was admitted to Burdwan Medical College and Hospital.

“We believe the nurse treated at Burdwan Medical College is the index case,” a health official said.

An index case, or “patient zero”, is the first infected individual identified by authorities during an outbreak, though experts note this may not be the primary source.

The nurse returned home to East Burdwan on December 31 with high fever and respiratory issues. While being treated at home, she fell unconscious on January 4. Family members took her to Burdwan Medical College and Hospital, from where she was transferred to the Barasat hospital on January 6 after her condition worsened.

“Investigation into the primary source continues. One theory suggests the nurses treated a patient at Barasat hospital with symptoms resembling Nipah, who later died. It is unclear if that patient had the virus,” a health official said.

He said a team could be sent to the village of one of the nurses, where the nurse attended a family event in December.

Nipah virus is primarily transmitted by fruit bats. Consumption of palm juice contaminated by bats is a known source. Human-to-human transmission can occur after prolonged contact, placing healthcare workers at higher risk.

Health department sources said one of the nurses is in a deep coma, and doctors are planning a tracheostomy, a procedure that creates an opening in the neck and into the windpipe to aid breathing. The second nurse suffered a convulsion on Tuesday evening, worsening the patient’s condition. “The patient briefly regained consciousness, but not for long,” a health official said.

Contact tracing has identified around 120 individuals who interacted with the confirmed patients. All are quarantine and being monitored, with health staff checking on them twice daily. Samples from about 60 people have been sent for testing.

The samples were initially sent to AIIMS Kalyani, but NIV Pune has established a mobile BSL-3 laboratory at Beliaghata ID Hospital to test for Nipah, a health official said.

While the virus is not as transmissible as Covid-19, it has a high fatality rate. According to the World Health Organization, the case fatality rate is estimated at 40–75%.