Monkeypox is a virus in the genus orthopoxvirus, which includes the variola virus that causes the disease smallpox. It was first identified in the late 1950’s in a research lab in Denmark that was studying polio using monkeys as animal subjects. These monkeys had been imported from Singapore. Subsequently, it was also identified in imported monkeys being used in laboratories in the United States and a zoo in Rotterdam. The first case in humans was identified in early 1970’s in the Democratic Republic of Congo.
Monkeypox causes small pustules (poxes) to form on the skin, primarily in the area of initial exposure. This is like other pox causing diseases such as cowpox, which was seen on the hands of people manually milking infected cows. That virus, vaccinia, was used to develop the vaccine against smallpox with its subsequent eradication in the world (expect for two biological weapons laboratories where it is still kept, one in the US and the other in Russia).
As with most of these viruses that “jump” from other species to humans, there was an intermediate animal between monkeys and humans and this appears to be small rodents. There was an outbreak in Western Africa between 1970 and 1980 that was carried to humans by squirrels. In 2003, there was an outbreak in the US involving 71 people in the states of Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin. This turned out to be due to a shipment of prairie dogs from Africa that were sold as pets. This was the first incidence of cases in the Western Hemisphere. Nine of the infected people required hospitalization, mostly for nausea and dehydration, with only two developing serious illness of viral pneumonia. All 71 recovered fully and there were no deaths. Of interest, during that outbreak there were 57 healthcare workers who took care of the few monkeypox patients who required hospitalization and none of these healthcare workers contracted the illness.
The current global outbreak was first identified in the United Kingdom in May, 2022. It appears that it may have been brought there from Nigeria by an international traveler and subsequently spread to others through close, intimate contact. Most of the initial cases in Europe involved men who have sex with men, suggesting the possibility of sexual transmission. Since May, it has been identified around the world with a total of just over 3,500 cases currently reported by the World Health Organization (WHO). In the US there have been 244 cases with 66 in California as reported by the CDC as of this writing. The majority of the US cases have been associated with international travel or imported animals. During this current global outbreak, there has only been one death worldwide and that was in Nigeria.
Human-to-human transmission is primarily through direct contact with the pustules. Rodent-to-human transmission may also involve contact with the infected animal’s urine or feces. Monkeypox is considered to be of low contagion, meaning that it really takes direct contact to transmit and even then the transmission rate appears to be less than 10%. For comparison, COVID’s initial Alpha strain had a transmission rate of 30% and the current Omicron variant is about 50%.
The incubation period is about 21 days between the time of infection and when symptoms of fever and a rash develop. The fever develops first with poxes forming in the area of exposed skin between 1 and 4 days later. In some cases, the rash spreads to involve the rest of the body, including the face. The pox pustules scab over and heal in 7 to 14 days, sometimes leaving a small scar. The person is considered to be contagious until all of the pustules have scabbed over.
Most of the deaths in humans have occurred in Africa during the 1970-1980 outbreak. These were almost all in children under the age of 10 and likely due to dehydration. There were also a few cases of death related to viral pneumonia or encephalitis in adults. These adults may have had other illness, such as AIDS, that compromised their immune systems.
In most people, the illness is self-limited, meaning that people are sick for a few weeks and then make a full recovery without any treatment. There are two antiviral drugs that can be used in more serious cases. There is also an antibody infusion that can be given post-exposure to people who may be at high risk for more serious illness, such as those with AIDS or other immune deficiencies.
A vaccine has also been developed. Interestingly, previous vaccination against smallpox is protective against monkeypox.
The WHO is not classifying this as a global health emergency at this time due to the fact that the illness is generally not severe and the disease is not easily transmitted. However, given the potential for viruses to change their behavior through mutation, it is a disease that the WHO and the CDC will definitely be watching closely.