Information on Monkeypox

September 8, 2022

Hokesen News Letter, No 231 August 30, 2022
Health Care Center, Tokyo University of Foreign Studies
Yasuhiro Yamauchi, MD, PhD

Monkeypox is an acute eruptive infectious disease that has been endemic in Central and West Africa since it was first confirmed in humans in 1970, and is currently classified as a Category 4 infectious disease under the Infectious Disease Control Law in Japan. So far, sporadic outbreaks have been confirmed in imported cases from outbreak areas, but it was thought that human-to-human transmission was rare and the chain of infection would soon cease. However, since early May 2022, a number of cases with no travel history and no confirmed epidemiological link to monkeypox have been reported from several countries, mainly in Europe and North America in short duration, over a short period of time, indicating that human-to-human transmission may be more likely to occur than previously assumed.

Monkeypox is an infectious disease caused by the monkeypox virus, which belongs to the genus Orthopoxvirus of the Poxviridae family. Two genetic clades have been identified, the Congo Basin clade and the West African clade. With the Congo Basin clade being more severe and highly infectious from human to human. While the current outbreak is classified as the West African clade, there is a possibility that the clinical course and the rate of severe disease in the outbreak from 2022 onward may differ from the previous reports, and caution is required.

The route of infection is through contact with animals carrying the virus, which infects humans. It can also be transmitted from human to human through contact with skin lesions, body fluids, or blood of infected people or animals (including sexual contact), prolonged exposure to droplets in clos face-to-face contact with the patient, or contact with bedding or other items used by the patient.

The incubation period is usually from 7 to 14 days, but can range from 5 to 21 days. Estimates based on the current outbreak report a median of 8.5 days.

Typical symptoms include fever, headache, myalgia, and enlarged lymph nodes, which persist for 0-5 days, and a two-phase course with the skin rash appearing 1-3 days after the fever. Lymph node swelling occurs in submandibular, neck, and groin areas. Skin eruption typically begins from face and to trunk, and it proceeds to papules (well-defined bump), vesicles (filled with clear fluid), pustules (filled with yellowish fluid), and crusts (dried up and fell off). In most cases, the disease lasts 2-4 weeks and resolves spontaneously, but it can become severe in children or depending on the degree of exposure, the patient's health status, and complications.

Moreover, in epidemics occurring since 2022, cases have been reported in which no prodromal symptoms such as fever or enlarged lymph nodes are seen, lesions are concentrated locally (perineum, perianal area, oral cavity, etc.) and no generalized rash is seen, or skin rashes in different stages are seen at the same time.

Diagnosis is based on detection of the monkeypox virus gene by PCR testing using the contents of the blister or pustule, the lid, or tissue.

Generally, symptomatic treatment is the standard method. There are no approved medicines available in Japan yet. In Europe, there are drugs approved for specific treatment, and specific clinical studies are being conducted in Japan. Complications such as pneumonia and cellulitis are treated as appropriate.

Prevention methods include the smallpox vaccine, which has been shown to prevent about 85% of cases of the disease. WHO also recommends smallpox vaccine as a post-exposure prophylaxis for monkeypox. In endemic areas, it is important to avoid direct contact with susceptible animals or infected persons.

For inquiries, please consult with the Health Care Center, TUFS.

Monkeypox(World Health Organization)