Epidemiology

• Caused by double stranded DNA virus, genus orthopoxvirus, closely related to smallpox and cowpox.
• Discovered in 1958 in monkeys with first human case recorded in 1970 in the Democratic Republic of Congo. (CDC) 
• It is a zoonotic disease , meaning it is transmitted from animal to humans, with primary reservoir in squirrels, Gambian poached rats, dormice, different species of monkeys and others. 
• First reported in the U.S. in 2003. Cases were related to pet prairie dogs that had been housed with monkeypox virus infected African rodents, imported from Ghana (WHO)
• There are 2 clades (having evolved from same ancestral line) of the disease. The current outbreak is from the West African lineage. (WHO)
• West African – milder disease, 1-3% fatality
• Congo Basin – severe disease, 10% fatality 
• Due to the similarity in the viruses, immunization against smallpox has been found to prevent infection with monkeypox. The WHO believes that increasing frequency of worldwide infection may be related to waning immunity against smallpox, since that disease was eradicated in 1980 and the vaccine is no longer popularly used. 

Transmission

• Animal to human – contact with sick or dead animals, ingesting poorly cooked meat of infected animals.
• Human to human -” Human-to-human transmission is thought to occur primarily through large respiratory droplets. Respiratory droplets generally cannot travel more than a few feet, so prolonged face-to-face contact is required. Other human-to-human methods of transmission include direct contact with body fluids or lesion material, and indirect contact with lesion material, such as through contaminated clothing or linens.” (CDC)

Symptoms

• Initial 1-3 days – fever, lymphadenopathy, back pain, headache, myalgias, fatigue
• 2-4 weeks of rash progression: macules -> papules -> vesicles -> pustules -> scabs
• The pox rash starts on the face and spreads to the rest of the body.

Testing

• Detection is by PCR testing, ideally of body fluid contained in the pox blisters.
• Test kits are available through local U.S. Health Departments and the CDC. All suspected cases should be reported to local authorities.

Treatment

• Treatment includes vaccinating anyone who has been exposed with the smallpox vaccine (ring vaccination). The general population is no longer routinely vaccinated due to side-effects of the smallpox vaccine.
• No current recommendation exists for antiviral therapy or smallpox immunoglobulin therapy.  
• See CDC recommendations 

Prevention

• The JYNNEOS vaccine was FDA approved in 2019 for adults > 18 against both smallpox and monkeypox. It is a 2 dose non-replicating attenuated virus that does not produce a lesion, and therefore can not cause transmission to others. The CDC Advisory Committee on Immunization Practices is currently evaluating vaccine data with a formal recommendation pending. Media reports note the U.S. government has ordered millions of doses. 
• The original smallpox vaccine (DRYVAX) is no longer in production. However, a second generation clone, ACAM2000, is produced by Synofi and approved by the FDA. The WHO notes that smallpox vaccine is 85% effective in preventing monkeypox.
• Vaccination is recommended for lab workers and anyone exposed to monkeypox. The CDC recommends vaccination within 4 days of exposure to prevent disease, with ACAM2000. However, vaccination between days 4-14 is also recommended to reduce disease severity. 
• Vaccination does carry risks. The CDC estimates “Based on past experience, it is estimated that between 1 and 2 people out of every 1 million people vaccinated will die as a result of life-threatening complications from the vaccine” (ACAM2000) but notes that disease fatally is 1-10% outweighing the risk of vaccination. 

Further Reading

• Current WHO Outbreak Tracker
• CDC Monkeypox Reference
• Johns Hopkins Monkeypox Reference