Endemic Monkeypox? Overall Decline, but Persistence Likely

Although the most likely scenario is that monkeypox cases will fall significantly in the next few months, transmission in the United States is “unlikely to be eliminated in the near future,” the Centers for Disease Control and Prevention (CDC) reports.

This apparent concession to some level of enduring endemicity of monkeypox comes in a “technical report” using forward-thinking assessments, modeling, and a deep dive into the available data.¹

The CDC has “moderate confidence” that “the most likely longer-term scenario is that the outbreak will remain concentrated in men who have sex with men (MSM), with cases slowing over the coming weeks, and falling significantly over the next several months. … We note that low-level transmission could continue indefinitely, and the cumulative number of cases that could occur among MSM is unknown.”

Variables that could affect this forecast include protective behavior and vaccine uptake of MSM, the group in which the outbreak emerged globally and that continues to transmit most infections.

“Based on analysis through Sept. 19, 2022, the growth rate of the monkeypox outbreak in the United States is slowing. We have high confidence in this assessment,” the CDC reports. “The slowing growth of the outbreak is likely due to a combination of many factors, including vaccination, behavior change, and possibly increases in infection-acquired immunity among a segment of the sexual networks at highest risk.”

Although the outbreak began primarily in white men, cases in the United States now reflect disproportionate disease in Black and Hispanic men. “Concurrent to this shift, there are increasing numbers of severe cases,” said Agam Rao, MD, FIDSA, an epidemiologist with the CDC. “We have seen this in people who are severely immunocompromised, mostly MSM with newly diagnosed HIV (human immunodeficiency virus) that is advanced.”

Populations that comprise the highest proportion of cases have received fewer vaccine doses, so vaccinating men in these minority groups is critical. With the hope of reducing stigma of a visible vaccination site on the forearm, Jynneos now can be administered in the deltoid region and the subscapular region of the back, she said.

The United States continues to have the most reported monkeypox cases of any country in world, with 26,049 cases as of Sept. 30, 2022. That represents a 60% increase since Aug. 10, when 10,392 cases were reported.¹ However, again, the outbreak is increasing at a slower rate. For comparison, the Aug. 10 case total represented an almost 10-fold increase over the 1,053 monkeypox cases reported on July 13, 2022.

Internationally, as of Oct. 5, 2022, there were 70,420 cases, with 69,702 identified in about 100 countries that have not traditionally seen monkeypox.

Of the U.S. cases in which gender was reported, 95% are men, with the remainder women and transgender women. “Most cases have been among men who report recent male-to-male sexual contact,” Rao said at a clinical briefing. “However, 20% of cases in men report no recent male-to-male sex.”

Although some of those cases may reflect the stigma of reporting, monkeypox can be spread to others by contact with infectious lesions, scabs, saliva, and, potentially, other bodily fluids of a patient with monkeypox. The virus also can be spread by touching items such as clothing or linens that previously touched the infectious rash or bodily fluids of a patient.

“At this time, there is no sustained spread outside of MSM networks,” Rao said. “We are keeping an eye out for this, but there has not been sustained spread reported in congregate settings like college dormitories or long-term care facilities. Regardless of these numbers, it is important for infection control practices and prevention education to be in place to ensure that there is no spread should cases occur.”

An orthopox virus akin to smallpox, monkeypox was so named after a colony of the primates became sick in a research lab in Denmark in 1958.² However, the name is a misnomer, since it is thought that the natural reservoir for monkeypox is in African squirrels and rodents.

In its technical report, the CDC raises the possibility that monkeypox could establish an animal reservoir in the United States.

“Several animal species in North America, both wild and domestic, may be susceptible to monkeypox infection and may be able to transmit the virus to other animals or species,” the CDC reported.

As part of research in this area, the CDC is investigating companion animals of monkeypox cases.

“CDC is working with partners in states and other jurisdictions to collect samples from animals that are present in the home while their owners are isolating due to monkeypox,” the report states. “A standard questionnaire is administered to examine risk factors for human-to-animal transmission and to assess if behavioral modifications following monkeypox diagnosis are associated with reduced likelihood of animal infection in the household setting. The findings will help create evidence-based guidance for public health and animal health professionals.”

Animals of monkeypox cases under study as of Sept. 29 include 17 dogs, two cats, and one rabbit.

REFERENCES

1. Centers for Disease Control and Prevention. Technical Report 3: Multi-national monkeypox outbreak, United States, 2022. Updated Sept. 29, 2022. https://www.cdc.gov/poxvirus/monkeypox/cases-data/technical-report/report-3.html
2. von Magnus P, Andersen EK, Petersen KB, Birch-Andersen A. A pox-like disease in cynomolgus monkeys. Acta Pathol Microbiol Scand 1959;46:156-176. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1699-0463.1959.tb00328.x