Can Casual Contact Spread Zika?

A mysterious Zika virus case suggests casual contact somehow transmitted the virus.

The first documented case of a Zika-caused death in the continental U.S. occurred last summer in Utah. And the circumstances surrounding it sparked a medical mystery, raising perplexing questions.

Zika can cause flu-like sickness and, rarely, neurological complications, but most of the time it produces no, or very mild, symptoms in adults. So why did the Utah man, who had a normally functioning immune system, became extremely sick and die quickly from the virus?

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What’s more, a second person who visited the elderly man in the hospital had no contact with the patient known to spread the virus and no risk factors for Zika exposure. Yet, he became sick with Zika seven days after the hospital visit. How did the second man become infected?

One possibility is that the virus can be transmitted in some circumstances through casual contact, according to a team of doctors from the University of Utah School of Medicine and researchers at ARUP Laboratories in Salt Lake City, who are investigating the fatal Zika case and the subsequent illness of the dead man’s visitor. Their report suggests Zika can sometimes be more infectious than previous known, leading to casual transmission of the virus.

There’s no doubt about how the 73-year-old caught the infection that killed him. When he was admitted to a hospital in Salt Lake City in June of 2016, doctors learned the man had returned eight days earlier from a trip to a coastal area of Mexico where Zika had been reported. He felt fine until suddenly becoming ill with abdominal pain, sore throat, body aches, diarrhea, low blood pressure, inflamed eyes, and other symptoms.

The patient told doctors he had been bitten by mosquitoes on his trip to Mexico. But because he was so severely ill, an infection with dengue or malaria — mosquito-borne viruses that are typically far more serious than Zika — was initially suspected to be causing the man’s illness. However, tests for those diseases proved negative. Later, Zika tests were positive.

The patient’s condition rapidly deteriorated. He developed renal and respiratory failure, an inflamed liver, and other organ involvement. And after just four days in the hospital, he died.

This fast death from a virus that is usually mild in adults was odd enough. But doctors were soon faced with another baffling occurrence related to the case when the deceased man’s visitor, a previously healthy 38-year-old man with no known illnesses, became sick a week later with conjunctivitis (inflammation of the outer part of the eyeball, a frequent symptom of Zika), fever, muscle aches, and a rash on his face. Lab tests revealed the man was infected with Zika.

Without any contact with mosquitoes — the typical way Zika is spread — how did he catch the virus? He had not traveled to an area where Zika was being transmitted in almost a year, and he hadn’t been sexually active with a partner who had been to areas where Zika was active, either. The only Zika virus exposure he could have had was simply visiting his elderly friend.

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The young man told doctors he’d helped a nurse move his friend in bed without wearing gloves, and he also wiped the elderly man’s eyes during a visit. But he reported no contact with the patient’s blood or other body fluids.

While researchers still don’t know specifically how the younger man contracted the virus from a hospital visit, there are several reasons they believe that’s what happened. First, the second case occurred 7 to 10 days after contact with the first patient — that’s how long symptoms of infection would typically arise after Zika exposure.

The researchers discovered the elderly man had an extraordinarily high level of Zika virus in his body, which could have made him extremely infectious.

“I couldn’t believe it,” said Sankar Swaminathan, MD, chief of infectious disease at the University of Utah School of Medicine. “The viral load was 100,000 times higher than what had been reported in other Zika cases and was an unusually high amount for any infection.”

This raises the possibility the huge amount of virus overwhelmed the patient’s immune system, causing his death. It also likely made him extremely infectious — potentially explaining how the second patient (who recovered from Zika) may have contracted the virus from casual contact with the elderly patient’s sweat or tears.

“This was the first recognized case, and a very rare one, of a secondary Zika virus infection acquired by contact with a sick person,” said Kimberly Hanson, MD, medical director at ARUP.

Swaminathan, Hanson, and colleagues who are investigating the case have also raised the possibility there could have been small differences in the strain of the Zika virus the elderly man contracted that caused it to be exceptionally aggressive.

“This rare case is helping us to understand the full spectrum of the disease and the precautions we may need to take to avoid passing the virus from one person to another in specific situations,” Swaminathan said. “We may never see another case like this one. But one thing this case shows us is that we still have a lot to learn about Zika.”

There’s no reason to be overly concerned about catching the virus from casual contact based on one reported incident and the Centers for Disease Control and Prevention (CDC) have not issued any new warnings about Zika infection. However, it’s important to recognize the well-documented ways you can catch Zika — primarily through mosquito bites and sexual contact with an infected person — and learn how to protect yourself from infections.

This is especially important if you could become pregnant, due to the known risks Zika poses to unborn babies. For more information, visit the CDC’s Zika Transmission and Risk page.

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