Scientists found evidence of the yellow fever virus in urine and semen samples almost one month after one São Paulo patient became infected. The problem? Scientists thought that a person infected with yellow fever was no longer contagious after ten days.
This discovery means that a person infected with the virus is capable of passing the infection to others longer than scientists thought. The present study is, in a way, a follow-up to another study where researchers found dengue virus and Zika virus in urine and semen samples in infected patients. For the Zika virus, scientists observed the pathogen persisting in semen for months.
"This detection is a matter for serious concern, above all because it suggests that the transmissibility period for yellow fever virus may be longer than expected in the case of an acute infection,” explained study author Paolo Zanotto.
The patient involved in the discovery is a 65 year-old Sao Paulo individual, who never entered the toxic phase of the disease. Researchers found viral RNA from yellow fever virus, usually tested for using blood samples, in urine and semen samples 15 and 25 days after the individual’s yellow fever symptoms first began.
Yellow fever, like Zika and dengue, is transmitted to people through the bite of a mosquito carrying the virus. Symptoms usually go away three or four days after they begin and include fever, chills, fatigue, headache, muscle pain, nausea, and vomiting.
Scientists still need to test more patients to further understand what this discovery means for yellow fever and its transmission. They will need to find out how often the virus persists for multiple weeks and just how long it can stay in the human body. Being able to understand these components of yellow fever infection will help scientists improve diagnostics for the disease.
Current methods for diagnosing yellow fever involve certain tests that look for viral RNA in the blood. One test, called ELISA, measures the blood levels of immunoglobulin M, a type of antibody produced in the immune response against pathogens.
However, over half of people infected with yellow fever never show symptoms, which often prevents them from getting tested. Scientists from the present study offer a non-invasive diagnostic option: detection of the virus in urine.
"Detection of the virus in urine has been used to confirm infection by other flaviviruses, such as West Nile, Zika and dengue. In the case of dengue, this method won't become standard yet because we aren't sure how many infected people do in fact have the virus in their urine,” Zanotto explained. “This must now be investigated.”