A new study has found presence of yellow fever virus in urine and semen samples from a patient who survived the disease was detected almost a month after the patient was infected.
The study is published in Emerging Infectious Diseases wherein researchers followed a 65-year-old patient in São Paulo who did not enter the toxic phase of the disease. The team found significant amount of viral RNA (genetic material) in the patient’s urine and semen 15 and 25 days after the initial symptoms of yellow fever appeared.
Previous studies led to discovery of presence of dengue virus and Zika virus in the urine of infected patients, as well as in their semen in the case of Zika. For this reason, we decided to see whether the same was the case for yellow fever virus, one of the authors said.
Scientists involved with the study say it is a matter for serious concern that the virus was found a month after infection as it suggests that the transmissibility period for yellow fever virus may be longer than expected in the case of an acute infection.
According to the current model, yellow fever virus transmissibility begins between 24 and 48 hours before the appearance of the first symptoms and lasts until between three and seven days thereafter. In most cases, the symptoms disappear after three or four days.
A small percentage of those infected enter a second, more toxic stage within 24 hours of recovery from the initial symptoms, and half of these die within a period of seven to ten days.
The researchers do not yet know what the implications of the presence of yellow fever virus in urine and semen may be, with what frequency this occurs, or how long it persists in these biological materials since they analyzed only one patient.
In the case of Zika, previous studies conducted in collaboration by Durigon’s and Zanotto’s groups showed that the virus remained in patients’ semen for months, with viral loads declining slowly. They also confirmed that Zika virus can be sexually transmitted.
They sequenced the genome of the virus isolated from the patient’s urine. The analysis showed that the virus belonged to a group of genotypes isolated in South America, including two isolated in 2017 in Espírito Santo State.
The researchers believe tests designed to detect the presence of yellow fever virus, especially in the urine of patients with suspected infection, can facilitate and improve diagnosis of the disease.
Clinical confirmation of incipient infection by yellow fever is currently based on detection of viral RNA in blood by serologic testing, real-time polymerase chain reaction (RT-PCR) assays or enzyme-linked immunosorbent assays (ELISAs), which measure blood levels of certain antibodies, such as immunoglobulin M (IgM), made by the immune system to combat invading microorganisms (antigens).
These tests are usually performed when patients with a suspected infection arrive at the hospital. More than 50% of people infected by yellow fever virus, however, do not display symptoms of the disease, such as high temperature, chills, fatigue, headache, muscle pain, nausea, and vomiting.
Detection of the virus in urine could facilitate and speed up diagnosis of these asymptomatic patients, especially in places where deaths from yellow fever have been reported, the researchers noted.
Testing urine and semen samples to diagnose yellow fever could also reduce false-negative results and strengthen the reliability of epidemiologic data during outbreaks of the disease, such as the ongoing outbreak in São Paulo and Minas Gerais states, they added.
Because detection of yellow fever virus in urine is non-invasive (in contrast to serology), it has proved useful and has become routine for several groups of researchers who are studying the current outbreak of the disease in São Paulo State, he added.
The researchers at ICB-USP, in collaboration with Professor Amaro Nunes Duarte Neto and several other researchers in the Pathology Department of the same university’s Medical School (FM-USP) led by Professor Paulo Saldiva, are verifying the presence of yellow fever virus in autopsy materials, including various cellular tissues, from patients diagnosed with yellow fever who entered the toxic phase of the disease.
Preliminary analysis of these materials points to significant amounts of the virus in various organs, including the brain.