By Rodney E. Rode, Texas State University, May 20, 2022
The first case of human monkeypox was reported in 1970 in the Democratic Republic of the Congo (DRC) during a period of intensified efforts to eradicate smallpox. Credit: CDC
On May 18, 2022, Massachusetts health officials and the Centers for Disease Control and Prevention (CDC) confirmed a single case of monkeypox in a patient who had recently traveled to Canada. Cases have also been reported in the United Kingdom and Europe.
Monkeypox is not a new disease. The first confirmed human case was in 1970, when the virus was isolated from a child suspected of having smallpox in the Democratic Republic of the Congo (DRC). Fortunately, smallpox is unlikely to cause a new pandemic, but given COVID-19, the fear of a new major outbreak is understandable. Although quite rare and usually mild, smallpox can still potentially cause serious illness. Healthcare professionals are concerned that more cases will increase with increased travel.
I am a researcher who has worked in public health and medical laboratories for more than three decades, especially in the field of animal diseases. What exactly is happening in the current epidemic and what does the history of monkeypox tell us?
Monkeypox causes lesions that look like pus-filled blisters that eventually become covered in scabs. Credit: CDC
Cousin of smallpox
Monkeypox is caused by the monkeypox virus, which belongs to a subgroup of viruses in the Poxviridae family called Orthopoxvirus. This subgroup includes smallpox, vaccine and vaccinia viruses. While the animal reservoir for the monkeypox virus is unknown, African rodents are thought to play a role in the transmission. The monkeypox virus has only been isolated twice from an animal in the wild. Currently, diagnostic tests for monkeypox are only available in the laboratories of the Laboratory Response Network in the United States and worldwide.
The name “monkeypox” comes from the first documented cases of the disease in animals in 1958, when two outbreaks occurred in monkeys kept for testing. However, the virus has not spread from monkeys to humans, nor are monkeys the main carriers of the disease.
Monkeypox belongs to the Poxviridae family of viruses, which includes smallpox. Credit: CDC
Epidemiology
Since the first human case was reported, smallpox has been found in several other Central and West African countries, with the majority of infections in the DRC. Cases outside of Africa involve international travel or importation of animals, including in the United States and elsewhere.
The first reported cases of monkeypox in the United States were in 2003 from an outbreak in Texas involving a shipment of animals from Ghana. There were also travel-related cases in November and July 2021 in Maryland.
Because monkeypox is closely related to smallpox, the smallpox vaccine can provide protection against infection from both viruses. Since smallpox was officially eradicated, routine smallpox vaccinations for the general population of the United States were discontinued in 1972. As a result, monkeypox is becoming more common in unvaccinated people.
Transmission
The virus can be transmitted through contact with an infected person or animal or contaminated surfaces. The virus usually enters the body through injured skin, inhalation or the mucous membranes of the eyes, nose or mouth. Researchers believe that human-to-human transmission occurs mainly through the inhalation of large respiratory droplets, rather than direct contact with body fluids or indirect contact through clothing. The degree of human-to-human transmission of monkeypox is limited.
Healthcare professionals are worried that the virus may now be spreading unnoticed through transmission in the community, possibly through a new mechanism or route. Where and how infections occur is still being investigated.
Signs and symptoms
Once the virus enters the body, it begins to reproduce and spread through the body through the bloodstream. Symptoms usually do not appear for one to two weeks after infection.
Smallpox causes skin lesions similar to smallpox, but the symptoms are usually milder than those of smallpox. Influenza-like symptoms are initially common, ranging from fever and headache to shortness of breath. One to 10 days later, a rash may appear on the limbs, head or torso, which eventually turns into blisters filled with pus. In general, symptoms usually last two to four weeks, while skin lesions usually form in 14 to 21 days.
While smallpox is rare and not usually fatal, one version of the disease kills about 10% of infected people. It is believed that the form of the virus that is currently circulating is milder, with a mortality rate below 1%.
Vaccines and treatments
The treatment of monkeypox is mainly aimed at relieving the symptoms. According to the CDC, there are no treatments available to treat monkeypox infection.
Because smallpox is closely linked to monkeypox, the smallpox vaccine can protect against both diseases.
Evidence suggests that the smallpox vaccine may help prevent monkeypox infections and reduce the severity of symptoms. A vaccine known as Imvamune or Imvanex is licensed in the United States to prevent monkeypox and smallpox.
Vaccination after exposure to the virus can also help reduce the chances of serious illness. Currently, the CDC recommends vaccination against smallpox only in people who have been or are likely to be exposed to monkeypox. Immunocompromised people are at high risk.
Written by Rodney E. Rode, Professor of Clinical Laboratory Science at Texas State University.
This article was first published in The Conversation.
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