(NEXSTAR) – As the monkeypox virus continues to spread throughout the United States, health officials are asking people at high risk of contracting the virus to stay vigilant and get tested.

The virus is known to cause a rash of bumps and blisters that can be painful, the Centers for Disease Control and Prevention says, but not everyone will see this visual signifier as their first symptom.

What are the signs and symptoms of the virus? According to the CDC, monkeypox is like a milder case of smallpox.

“The main difference between symptoms of smallpox and monkeypox is that monkeypox causes lymph nodes to swell (lymphadenopathy) while smallpox does not,” the CDC writes. Lymph nodes can swell as the result of any infection, Mayo Clinic explains. They’re located throughout your body, from your neck down to your armpits and groin.

In the early stages of infection, monkeypox symptoms can include:

  • Fever
  • Headache
  • Muscle aches
  • Backache
  • Swollen lymph nodes
  • Chills
  • Exhaustion

A few days in, a rash typically starts to develop, according to the CDC. The rash will often start on people’s face or genitals and then spread to the rest of the body. At first, they may look like pimples or blisters, and the bumps may be painful or itchy, the CDC says.

The bumps from the rash will eventually scab over and fall off.

Not everyone who contracts monkeypox will see the same symptoms in the same order. “Sometimes, people have flu-like symptoms before the rash,” the CDC explains. “Some people get a rash first, followed by other symptoms. Others only experience a rash.”

Symptoms usually start to show up within three weeks of being exposed to the virus. The full cycle of illness usually lasts between two and four weeks, the CDC says.

If you have an unexplained rash fitting the description of monkeypox, the CDC recommends seeing a doctor. In the meantime, the agency advises avoiding sex or intimate contact with other people.