The Virus:
- Family: Poxviridae
- Subfamily: Chordopoxvirinae
- Genus: Orthopoxvirus
- Species: Monkeypox virus
- Brick-shaped virus , surrounded by a lipoprotein envelope with linear double-stranded DNA genome
- Genetically distinct from other viruses of the Poxviridae family (i.e. variola, vaccinia, ectromelia, camelpox, and cowpox)
- There are two distinct clades of monkeypox virus [3]
- West African: More favorable prognosis with case fatality rate <1%
- Central Basin: more lethal, with a case fatality rate of up to 11% in unvaccinated children
Image from Science Website [Link is HERE]
Epidemiology/Transmissibility:
- 1st identified in monkeys in 1958
- 1st human case reported in 1970
- Endemic in areas of Africa
- Typically, only see sporadic cases outside of Africa in people who have traveled to certain regions or have been in close contact with those travelers
- From the 1970s up until 2003, sporadic cases were identified in central and western Africa
- Before 1980, case-fatality rate was 17% and secondary transmission was the cause in 9% of cases
- From 1981 to 1986, the case-fatality rate was 10% and secondary transmission was the cause in 28%
- From 1996 to 1997, the largest outbreak of human monkeypox occurred, which had a case-fatality rate of 1.5% and secondary transmission was the cause in 78%
- The 2003 outbreak, was the first documented cases in the western hemisphere with a case-fatality rate of 0% and secondary transmission was the cause in 0%
- Cases of Monkeypox in 2022 from May 6th – 20th [2]:
- UK: 20 (Confirmed)
- Spain: 23 (Unconfirmed)
- Portugal 5 (Confirmed) + 15 (Unconfirmed)
- US 1 (Confirmed)
- Precise prevalence and incidence are limited (But both have increased since the discontinuation of routine smallpox vaccination)
- Wide range of hosts which has allowed a reservoir in wild animals and some sporadic cases in humans
- In contrast to smallpox, monkeypox associated with low transmissibility between human beings
- Mode of transmission remains poorly characterized:
- Large respiratory droplets most likely mode of transmission
- Direct contact through bodily fluids also possible
- The likelihood of transmission between individuals without prolonged close contact is considered to be low
Hosts/Reservoirs:
- Primary reservoir is thought to be squirrels, non-human primates, prairie dogs, rabbits, and rats
- Primary reservoir for human infection remains unknown
Who to Suspect:
- Travelers to known endemic areas
- Anyone in contact with a traveler to a known area
Clinical Features:
- Clinically monkeypox is almost indistinguishable from smallpox, chickenpox, and other causes of vesiculopustular rashes
- Typical incubation period 10 – 14 days (up to 21 days)
- Infectious period occurs during the 1st week of the rash
- 2-day prodrome manifested by fever, malaise, and lymphadenopathy typically occurs before development of rash
- Lymphadenopathy is key distinguishing characteristic of human monkeypox compared to smallpox
- 90% of patients infected with monkeypox develop lymphadenopathy (Typically in submandibular, cervical, postauricular, axillary, or inguinal areas)
- Rash begins as maculopapular lesions of 2 to 5mm in diameter
- Typically, centrifugal pattern (from the torso outwards)
- Can be monomorphic (like smallpox) or pleiomorphic (like chickenpox)
- Skin lesions typically progress from popular, to vesicular, to pustular, and crust phases over a 14-to-21-day period
- In patients with smallpox vaccination the rash will be milder and only ≈50% will have lymphadenopathy
- Most patients will not become seriously ill
- In the 2003, US outbreak (81 confirmed cases) there were zero deaths [1]
- Mortality seems to be higher in children, young adults, and immunocompromised individuals
- Generally, cases are mild, and people tend to recover within weeks
Monkeypox vs Chickenpox vs Measles
Complications:
- Bacterial superinfection of skin
- Skin scarring
- Corneal scarring/vision loss
- Pneumonia
- Dehydration (secondary to painful oral lesions and insensible fluid loss)
- Encephalitis
- Death (Very rare)
Diagnosis:
- Skin biopsy tissue and/or blood
- At a minimum, 2 scabs or material from vesicles should be collected in separate sterile containers
- DNA-based tests, such as PCR with sequencing, is the most precise method available for orthopoxvirus identification and species assignment
- Serological testing for monkeypox antigens is difficult because of close antigenic relation between surface antigens among orthopoxviruses
Treatment/Management:
- There is no proven treatment for monkeypox
- For contacts of a case, recommend twice daily fever/symptom monitoring for 21 days + Isolation recommended
- Currently, CDC recommending airborne and contact precautions (i.e. negative pressure room, N95, gloves, and eye shield)
- Pre-exposure smallpox vaccination has been shown to confer 85% protection against monkeypox [1]
- Role of post-exposure smallpox vaccination is less clear
- According to the CDC, vaccination within 4 days of exposure may prevent disease onset and vaccination within 14 days may reduce disease severity [3]
- Vaccinia immune globulin has no available data on effectiveness in the treatment of monkeypox
- For severe cases, antiviral agents with known activity against orthopoxviruses in animal studies (No published data on its effectiveness for treatment on human monkeypox)
- Cidofovir a broad-spectrum antiviral agent with in-vitro activity against virtually all DNA virsuses
- Brincidofovir an oral DNA polymerase inhibitor
- Tecovirmat an oral intracellular viral release inhibitor
References:
- Di Giulio DB et al. Human Monkeypox: An Emerging Zoonosis. Lancet Infect Dis 2004. PMID: 14720564
- Mahase E. Monkeypox: What do we Know About the Outbreaks in Europe and North America? BMJ 2022. PMID: 35595274
- Moore M et al. Monkeypox. StatPearls 2021. [Link is HERE]
For More on this Topic Checkout:
- First10EM: Monkeypox
Post Peer Reviewed By: Anand Swaminathan, MD (Twitter: @EMSwami)
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