– An outbreak of the deadly Ebola virus in the West African nation of Guinea has reached the crowded capital, Conakry, prompting new fears about its spread, health officials said Tuesday.

Over the past month, the disease has traveled from Guinea’s remote forest regions near the Liberia and Sierra Leone borders and has already killed 83 people, including four in Conakry.

Now, with 13 cases in a densely populated capital of 2 million people, health officials say the challenge of containing the outbreak has become more acute. Ebola has killed hundreds in rural Central Africa over the past four decades, but it is unusual for it to reach urban centers.

Residents of Conakry said Tuesday that disquiet had set in, though markets were crowded and the capital’s monstrous traffic jams continued unabated. Some were carrying around small bottles of bleach, people were avoiding shaking hands, and pharmacies were selling out of hand sanitizer.

“In Conakry everybody is worried,” said Fodé Abass Bangoura, a lawyer with an office downtown. “I’m avoiding physical contact with people, and I’m eating at home.”

Even more worrying than the presence of Ebola in Conakry is its deadly presence at both ends of the country.

“It’s the combination of having quite a number of cases, and also the geographical dispersion,” said Dr. Hilde de Clerck of Doctors Without Borders, the global medical charity. “Now that it has reached Conakry, it is also special, and a bit more scary.”

Senegal has closed its border with Guinea. About half a dozen suspected cases and two confirmed cases have been identified in neighboring Liberia.

The Ebola virus is rare but deadly. Its point of origin is often the consumption of bush meat, and it has a fatality rate of up to 90 percent. Human transmission occurs through contact with bodily fluids.

Death is painful, with high fever, severe headache, vomiting, diarrhea and profuse bleeding. Health workers are often among the first to die, and they must take extraordinary precautions to avoid being infected.