In a recent study published in The Lancet Infectious Diseases, researchers described patients with monkeypox virus (MPXV) infection.
Monkeypox (MPX) is a zoonosis first identified in monkeys in the late 1950s. The first human case of MPX was a child from the Democratic Republic of Congo in 1970. MPXV causes a disease similar to smallpox but has a lower mortality rate for cases reported after 2000.
MPX is endemic in Central and West Africa, although sporadic cases have been reported in high-income countries due to international travel and the exotic pet trade.
However, more than 60,000 cases of MPX have been reported since May 2022 in countries without historical cases, particularly in the United States (US) and Europe, among those with no travel history to endemic areas. In the current outbreak, men who have sex with men (MSM) appear disproportionately affected by MPX, with a significant proportion of whom have attended mass gathering events.
MPXV spreads through contact with bodily fluids, respiratory droplets, and lesions. MPXV is also transmitted via sexual activity. Understanding how the virus spreads is crucial to control its transmission.
About the study
In the present study, researchers evaluated the MPX patients who acquired infections locally in France, emphasizing virus distribution in the body. Patients were tested for MPX using samples from three different anatomical sites at diagnosis (day 0 or D0). Infection status was confirmed based on a positive MPXV polymerase chain reaction (PCR) test from any anatomical site. All patients were re-tested two weeks (D14) after D0.
Samples for re-testing were from the same lesions from the initial diagnosis (D0) in cases where the lesions were still present. Re-test samples were not collected if the lesion was absent. The study’s primary outcome was the proportion of positive samples at D0. Secondary outcomes included the proportion of positive samples from D14 and the cycle threshold (Ct) values of positive samples from D0 and D14.
Fifty males with confirmed MPX provided 356 samples from May 20 to June 13, 2022. All except one were MSM. Twenty-two (44%) were negative for human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP), 22 were categorized as people living with HIV, and six were HIV-negative without PrEP. Patients did not receive specific antiviral therapy for MPX. Twenty-four samples were subject to genome sequencing, and all MPXV genomes were of the West African clade.
All patients had skin lesions, and half of the cohort had lesions localized near the genitalia/anus. There were 249 samples collected at D0 with a median of five days since symptom onset. MPXV detection was more frequent in the skin (88%), throat (77%), and anus (71%) than in blood, urine, or semen. There were five patients with undetectable virus from skin samples but tested positive on anal or throat samples. More than half of the semen samples were positive for MPXV.
Skin lesion samples had significantly higher viral loads (Ct – 19.8) than throat, blood, or semen samples. Similarly, a high viral load was noted in semen samples of patients with genital lesions, anal samples from patients with anal ulcers, and throat samples from patients with tonsilitis. Twenty-four patients were retested at D14. There were 100 paired samples, that is, collected from the same lesion. At D14, most anal (91%), urine (95%), and semen (82%) samples and all throat and blood samples were negative or weakly positive for MPXV.
Consistent with the evidence from the ongoing MPX outbreak, most patients were MSM and reported multiple sex partners in the past 21 days, corresponding to the maximum incubation period of MPX. In line with this, most semen samples at diagnosis (D0) were MPXV-positive, suggesting a possible transmission mode through male sexual secretions.
Moreover, MPXV was detected in anal and oropharyngeal samples, concordant with the evidence of transmission through anal and oral sexual activity. There were significant differences in viral load across samples. Skin, semen, and anal samples showed high viral loads. Re-testing two weeks after initial diagnosis indicated rapid viral clearance from body fluids.
The authors posit that a short viremic phase occurs at the beginning of the symptomatic stage, and systemic viral clearance occurs before the skin lesions heal. Overall, these findings contribute to the growing evidence of sexual activity-linked transmission of MPXV.