Mpox (formerly monkeypox) is a virus infection caused by Monkeypox virus, a double-stranded DNA orthopoxvirus related to variola, vaccinia, cowpox and Borealpox viruses. There are 2 main Mpox clades: Clade I, endemic to Central Africa and Clade II, to West Africa. Clade I is associated with more severe and Clade II with less severe disease.

In 2022 cases of Mpox Clade II were reported in North America and Europe. More recently, Clade I cases are reported in Europe and the US. Clade II Mpox is now reported in >100 countries with >100,000 cases worldwide and >500 deaths. The World Health Organization (WHO) has declared Mpox a Public Health Emergency of International Concern (PHEIC).

Human-to-human transmission of Mpox is the most common route outside Africa. Transmission occurs by contact with skin of an infected, usually symptomatic person. However, transmission can also occur via clothing, bedding, towels, dishes, cutlery and by saliva. There is also transmission via sexual contact among people who are gay or b-isexual.

Diagnosis of Mpox infection is by polymerase chain reaction (PCR)-testing with virus-specific DNA primers and probes. Persons with a positive orthopoxvirus virus PCR test should have additional testing to exclude related infections such as coxpox and Borealpox.

Symptoms of Mpox infection are protean including a painful rash which starts as raised spots turning into ulcers and liquid-filled blisters which eventually form desquamating scabs, fever, headache, myalgias, enlarged lymph nodes, rigors, fatigue and arthralgias. Pharyngitis and proctitis may be presenting symptoms.

Clade II cases are typically self-limited but this is not so of Clade I infections which may require medical intervention with anti-virals such as tecovirimat and cidofovir. Smallpox vaccination may attenuate severity of Mpox infections and is recommended in health care workers and others likely to be in close contact with Mpox-infected persons.

Isolation of known or suspected cases is critical. Currently, there is no vaccine. It is important to report all suspected and proven cases to local and national Health Authorities.

Persons with haematological cancers, especially those receiving chemotherapy and other immune-suppressive therapies are at increased risk of Mpox infection. They are also at increased risk of severe adverse effects from Clade I and even Clade II infections. Precautions should resemble those used to protect people with haematological cancers from herpesvirus infections. Haematologists in Africa should be especially alert to the possibility of Mpox infection in their patients. Transmission of Mpox to physicians is reported but is rare. The Centres for Disease Control and Prevention (CDC) recommends physicians wear a gown, gloves, eye protection and an N95 respirator whilst caring for people with suspected or proven Mpox infection.

Although no cases of Mpox in people with haematological cancers are reported yet the rapid spread of Clade II infections worldwide makes this likely to occur. Also, the protean manifestations of Mpox make it likely a correct diagnosis might be missed. We urge haematologists to keep Mpox infection in mind when caring for people with haematological cancers.