Early in the monkeypox outbreak, a man in his 20s arrived at an emergency department in Northern California, tiny blisters on his lips, hands and back. Within 12 hours, doctors diagnosed him with monkeypox.

That’s where their certainty ended. The patient did not have fever, aches, weakness, pain or other symptoms typical of the disease. He did not know when or how he had become infected. He had not had sexual contact with anyone for months, he said, and had not touched — as far as he knew — anyone with pox, as the lesions are called, or other symptoms.

At the onset of the outbreak, scientists thought they knew when and how the monkeypox virus was spread, what the disease looked like and who was most vulnerable. The 47,000 cases identified worldwide have upended many of those expectations.

Monkeypox patients have turned up with what looked like mosquito bites, pimples or ingrown hairs, not the large pustules usually associated with the infection. Some did not even have visible lesions but felt excruciating pain when swallowing, urinating or emptying their bowels.

Some had headaches or depression, confusion and seizures. Others had severe eye infections or inflammation of the heart muscle. At least three of the six deaths reported so far were linked to encephalitis, an inflammation of the brain.

“We really are seeing a very, very wide range of presentation,” said Dr. Boghuma Titanji, an infectious disease physician at a clinic in Atlanta that serves people living with H.I.V.

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