HOUSTON, Oct. 2 -- Health officials in the U.S. state of Texas said Thursday that they were monitoring about 80 people who had either direct or indirect contact with the first U.S. Ebola patient for signs of the disease.

These people have been asked to report to Texas health officials or the U.S. Centers for Disease Control and Prevention if they show symptoms of the deadly virus, Erikka Neroes, a spokeswoman for Dallas County Department of Health and Human Services, told the media on Thursday morning.

Earlier, officials said up to 18 people had close contact with Thomas Eric Duncan, the first U.S. Ebola patient identified as a middle-aged male from Liberia. Duncan, who traveled to Dallas to visit relatives and fell ill on Sept. 24, was confirmed to be infected with Ebola at a Dallas hospital Tuesday and was listed in serious but stable condition on Wednesday.

None of the 80 people who had direct or indirect contact with Duncan has shown symptoms of Ebola, U.S. authorities said. Nor had the patient relayed the deadly virus to paramedics who rushed him to hospital in ambulance or communicated the disease to anyone who took care of him in the hospital.

Health officials have issued legally-binding orders late Wednesday, asking four family members of Duncan to stay home and not have any visitors until at least Oct. 19, when the incubation period should be over. It can take as long as 21 days for Ebola symptoms to show up.

Authorities are calling for calm as panic set in after officials said Wednesday that five students who had close contact with the Ebola patient went to four different schools this week. Though officials assured it's highly unlikely that the five students could be infected, some parents and students told the media they were reluctant to go back to school Thursday.

The U.S. Centers for Disease Control and Prevention has sent a crew of infectious disease experts to Dallas to help local agencies deal with the case.

Ebola, which is spread via contact with bodily fluids, can have symptoms such as fever, muscle pain, vomiting and bleeding. It has infected 7,718 people and killed 3,338 since its outbreak in West Africa this year, according to figures from the World Health Organization.