Epidemiological, clinical and virological characteristics of four cases of monkeypox support transmission through sexual contact, Italy, May 2022

In May 2022, monkeypox did something it had never reliably done before. It spread through countries where it had no business being, such as Europe, North America, and Australia, in a sustained outbreak that caught public health systems off guard. Antinori and colleagues at Italy's National Institute for Infectious Diseases identified four of those cases within a five-day window between May 17 and 22. What they documented in those four patients became one of the early detailed looks at what this outbreak actually was. All four patients were men in their thirties who have sex with men. Two were living with HIV and on effective antiretroviral therapy. The other two were HIV-negative and taking pre-exposure prophylaxis, known as PrEP, which blocks HIV infection. All four had traveled in the first two weeks of May. Three had attended a mass gathering event on Gran Canaria, while one had traveled for sex work. During these trips, all four reported condomless sexual intercourse with multiple male partners. They also had a prior history of sexually transmitted infections. The epidemiological picture, before a single lab result came back, was already pointing somewhere. Then came the clinical presentation, and it was not what the textbooks described. Classical monkeypox typically begins with fever and swollen lymph nodes, followed by a generalized rash that spreads from the face outward. What Antinori's team observed was different. The lesions in all four patients were concentrated in the genital and perianal areas. Patient 1 had deep-seated, well-circumscribed lesions with central umbilication — meaning each lesion had a small central dimple — on the genital area, plus scattered lesions on the chest and calf. Patient 2 developed perianal lesions and then multiple anal lesions, with additional ones on the back and legs. Patient 3 had clustered itchy papules around the anal region, plus single lesions across the body. Patient 4 developed vesicular lesions on the genitals, followed by lesions in the suprapubic area and chest six days later. Beyond the location, the timing was unusual. Across all four patients, different lesions on the same body were at different stages simultaneously — what the authors refer to as asynchronous evolution. A lesion would begin as a raised, itchy papule secreting serous fluid, develop that central dimple, widen, then open and scab over roughly two weeks after symptom onset. But neighboring lesions would be at earlier or later stages at any given moment, rather than progressing in unison. Systemically, the illness was mild. One patient had no systemic symptoms at all. Two had fever, and one had muscle aches. All four recovered without specific antiviral therapy. Patient 2 received anti-inflammatory and antihistamine drugs for perianal pain and itching — that was the extent of treatment. Now, here is where the laboratory findings sharpen the picture considerably. The team collected samples from across the body: skin and lesion swabs, nasopharyngeal swabs, serum, plasma, saliva, feces, scabs, and seminal fluid. They ran a real-time polymerase chain reaction assay — the molecular method that detects viral genetic material — using two validated assays and reported results as quantification cycle values, or Cq values. A lower Cq means more viral DNA was detected. Skin lesions and scabs yielded very low Cq values, indicating high viral DNA levels — a scab from one patient came back at Cq 13.1, and a genital lesion at 15.6. Those numbers are not surprising; you'd expect the lesions themselves to be loaded with virus. What mattered more was what they found in the seminal fluid. Patient 1 tested positive in semen on day nine after symptom onset, with a Cq of 30.1. Patient 2 was positive on day five at Cq 29.4, and again on day nine. Patient 3 was positive on day six at Cq 29.3 and day eight at Cq 27.7, then negative on day eleven. The Cq values in semen, hovering around 27 to 30, were in the same range as the nasopharyngeal swabs from these same patients. That's the key comparison. The virus wasn't appearing in semen at barely detectable trace levels; it was showing up at concentrations comparable to what was coming from the respiratory tract. Antinori and colleagues are careful about what this means. Finding viral DNA in semen is not the same as proving that semen transmits infection. They cite work by Matusali and colleagues and by Le Tortorec and colleagues, showing that many viruses which cause viraemia — meaning the virus circulates in the bloodstream — can seed the male reproductive tract without sexually transmitting disease. The testes are an immunologically privileged site, where the immune system operates differently and viruses can persist. The Cq values observed make viral isolation unlikely, meaning actually culturing live, replicating virus from these semen samples would be a long shot. The correlation between Cq value and infectious viral load for monkeypox virus is simply not yet known. So the team sequenced the virus to understand where it fits in the outbreak's larger picture. For the first three patients, they Sanger-sequenced the complete haemagglutinin gene — think of this as a shorter molecular fingerprint useful for rapid classification. For Patient 1, they went further, assembling a full genome of 190,280 nucleotides from next-generation metagenomic sequencing, with a mean coverage of 159 reads. That genome was deposited on GenBank with the identifier ON614676.1. They then built maximum-likelihood phylogenetic trees, or evolutionary family trees, using one thousand bootstrap replicates to assess confidence, comparing their sequences against dozens of reference sequences from known monkeypox clades and from other May 2022 cases reported in Belgium, Germany, Portugal, and the United States. The Italian sequences grouped clearly within the West African clade of monkeypox virus. This matters for two reasons. First, the West African clade is less lethal than the Central African clade — case fatality rates in immunocompetent individuals are substantially lower. Second, the Italian sequences clustered with the contemporaneous European and American sequences, not with older or geographically unrelated strains. These were not four independent introductions. The Italian cases were part of a single, linked chain of transmission that had recently moved into non-endemic countries and was spreading through connected networks. Taken together, the epidemiology, clinical picture, and virology all point in the same direction — toward sexual networks as the primary amplifier of this outbreak. All four men reported condomless sex with multiple partners during travel. Their lesions appeared first and most prominently at genital and perianal sites, consistent with local inoculation during sexual contact. Monkeypox virus DNA was present in their semen at concentrations comparable to nasopharyngeal samples. And their viral sequences place them squarely within the outbreak spreading across Europe in May 2022. The paper concludes that close physical contact within sexual networks is the most plausible explanation for what they observed, while being precise about the limits of the evidence. Whether the route is direct skin-to-skin contact during sex, transmission via semen, or some combination, the data cannot yet determine. What they can say is that the hypothesis of biological contamination of semen samples is excluded, and that the lesion distribution and reported exposures are consistent with sexual transmission. What makes this paper valuable beyond the four cases it describes is what it modeled for outbreak science: early, granular case documentation that captures clinical presentation, multi-site viral detection, and genomic placement simultaneously. Each piece of evidence alone would be suggestive. Together they form a coherent argument. Antinori and colleagues close with a direct call — further studies are urgently needed to assess the presence, persistence, and contagiousness of monkeypox virus in different body fluids. In the opening weeks of a novel outbreak, four patients and a careful team asking the right questions can move the science faster than any single large study. That's exactly what happened here. This lecture was created by ennepō. 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