Scientists detect replication-competent Oropouche virus in semen of traveler, sparking transmission fears

New findings reveal the presence of replication-competent Oropouche virus in semen, posing fresh questions about sexual transmission risks and public health safety.

Background

Oropouche fever is endemic to the Amazon basin, but outbreaks have spread to countries like Brazil, Peru, Panama, and beyond, with over half a million cases since its discovery.

OROV is an emerging zoonotic arbovirus from the Simbu serogroup of the genus Orthobunyavirus, family Peribunyaviridae. Its natural hosts include nonhuman primates, some wild birds, and pale-throated sloths. OROV is primarily transmitted by biting midges, such as Culicoides paraensis and Culex quinquefasciatus mosquitoes. Symptomatic Oropouche fever resembles an influenza-like illness, with possible self-limiting meningitis or meningoencephalitis (inflammation of the brain and its protective membranes). While endemic to the Amazon Region, over 9,852 confirmed Oropouche cases have been reported in Brazil, Bolivia, Peru, Colombia, Cuba, and the Dominican Republic as of September 2024. Further research is needed to understand the implications of OROV, particularly regarding vertical transmission and adverse pregnancy outcomes.

About the Study

In August 2024, a 42-year-old man from Italy was evaluated for acute febrile illness after returning from Cuba, where he traveled from July 19 to 29. He experienced high fever, headache, and general malaise shortly before his return, with symptoms reemerging four days after onset. Clinical evaluations indicated no meningeal irritation, rash, or lymphadenopathy (swollen lymph nodes).

Laboratory tests yielded negative results, including blood cultures and specific real-time reverse transcription polymerase chain reaction (RT-PCR) for other arboviruses. However, Oropouche fever was confirmed through two OROV-specific RT-PCRs, with positive results in serum, whole blood, and urine collected four days post-symptom onset. Prolonged viral ribonucleic acid (RNA) shedding was noted in blood and urine samples, while fresh semen samples revealed higher OROV RNA levels. Notably, infectious OROV was cultured from the semen under Biosafety Level 3 conditions, confirming replication competence.

Study Results

The evaluation of the 42-year-old man revealed significant clinical findings related to OROV infection. Upon his admission to the Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) Sacro Cuore Don Calabria Hospital on August 2, 2024, he presented with an acute febrile illness that began shortly after returning from Cuba. Initially, the patient experienced a high fever of 39.0°C, headache, and general malaise. Although his fever subsided after two days, it recurred four days after symptom onset, but his neurologic examination remained unremarkable throughout.

Laboratory investigations showed a leukocyte count within normal reference limits and no signs of thrombocytopenia (low platelet count in the blood). Blood cultures returned negative results, and specific RT-PCR assays for dengue, chikungunya, and Zika viruses were also negative. However, Oropouche fever was diagnosed through two OROV-specific RT-PCRs targeting the small genomic segment, confirming the virus's presence in whole blood, serum, and urine samples collected on day four of symptom onset. The patient demonstrated clinical improvement and was symptom-free by day ten.

On days ten, sixteen, and thirty-two after symptom onset, RT-PCR results indicated persistent OROV RNA in whole blood and urine. While serum samples were positive for OROV RNA on day ten, they were negative on day sixteen, suggesting a decrease in viral load. Notably, fresh, unfractionated semen samples collected on days sixteen, thirty-two, and fifty-eight consistently showed higher viral RNA levels than those found in urine and whole blood. The cycle threshold (Ct) values for the semen samples were 25.4 on day sixteen, 28.9 on day thirty-two, and 34.1 on day fifty-eight, indicating ongoing viral shedding.

On day sixteen, infectious OROV was isolated from the semen sample using cell culture techniques under Biosafety Level 3 conditions. This isolation was confirmed by the observation of clear cytopathic effects (CPE) after five days and a marked increase in OROV RNA levels in the spent cell growth medium. Although viral RNA shedding continued to be higher in semen compared to urine and whole blood on day thirty-two, the ability to demonstrate replication competence had ceased by this time.

Conclusions

Oropouche fever outbreaks are explosive and swift, making it the second most frequent viral disease in Brazil after dengue fever.

To summarize, the study highlights the prolonged shedding of OROV RNA in multiple body fluids, particularly in semen, with the detection of replication-competent virus in a patient returning to Italy from Cuba. These findings raise significant concerns regarding the potential for sexual transmission of OROV. However, the study authors caution that the clinical relevance of these findings remains uncertain, as replication-competent virus was only detectable early in the infection, and more data are needed. The implications for public health are noteworthy, particularly in the context of sperm banking and assisted reproductive technologies. Further longitudinal studies are required to establish how frequently infectious OROV may be shed in semen and its potential risks in sexual transmission.