Dr. Matt Binnicker, an expert in the diagnosis of infectious diseases, discusses how testing for monkeypox is performed and how it differs from Covid-19.
Monkeypox virus, once considered a rare viral infection mainly confined to the continent of Africa, has now been confirmed in over 28,000 cases worldwide, including more than 7,500 in the United States. Last week, the Biden Administration declared monkeypox a public health emergency, including plans to expand the availability of vaccines and testing.
As of right now, the only way to confirm a positive monkeypox case is to send a sample to a lab, which is why the Centers for Disease Control and Prevention (CDC) recently partnered with 5 commercial labs to expand testing capacity.
Monkeypox is spread primarily through direct contact with a lesion (or rash) that contains the virus. Many cases in the current outbreak have been associated with sexual transmission of the virus. The disease can also be transmitted through contact with a contaminated object, such as a bedspread, a towel, or clothing, that a person with monkeypox has recently used.
Once exposed, an individual may develop a flu-like illness (fever, headache, and body-aches) within a week or two of being infected. Shortly thereafter, usually within a few days of initial symptoms, a rash will develop, which can be isolated or found on multiple parts of the body. The rash can persist for several weeks, and a person is considered contagious until the rash has completely healed.
While many Americans now rely on at-home tests to diagnose Covid-19, it’s unlikely we’ll see at-home tests for monkeypox anytime soon. Here are some of the key differences when it comes to testing for monkeypox versus Covid-19.
How is monkeypox testing performed?
Throughout the pandemic, the world has become more familiar with various types of lab tests to diagnose Covid-19, including PCR, antigen, and serology (also known as antibody) tests. One of those tests, PCR, is also the recommended method to diagnose monkeypox.
Despite the similarities between the technology used to detect monkeypox and Covid-19, there are important differences. First, the virus that causes Covid-19 is most commonly found in the respiratory tract, meaning the nose, throat and lungs, whereas monkeypox virus is most prevalent in a skin rash. Therefore, if someone is suspected of having monkeypox, their physician will use a swab to collect cells from the rash and then send the swab to a testing lab.
The lab will first separate any monkeypox virus DNA from the cells and proteins that are also present. The PCR test then “looks for” a small piece of the viral DNA (unique to monkeypox virus), and if present, that specific region of the virus’ genome is copied – or amplified – thousands, and potentially millions, of times. Every time a new copy is made, a fluorescent signal of light is produced, and eventually enough light is generated for the PCR test to be positive.
A second key difference is that PCR and antigen tests have been used extensively throughout the Covid-19 pandemic to identify people who were infected but asymptomatic, meaning lacking symptoms of disease. In contrast, monkeypox is not known to be efficiently transmitted from those who lack symptoms, so it’s unlikely that asymptomatic testing will be common as the monkeypox outbreak unfolds.
Will we soon have access to at-home tests for monkeypox?
Over the past year, there has been a rapid expansion in the availability of at-home tests to diagnose Covid-19. Americans even have the option of ordering free antigen tests that will be shipped directly to their home. Will at-home tests for monkeypox soon become a reality? The short answer is it’s unlikely. Most at-home tests are antigen-based, meaning they test for a viral protein that may be present in the sample. Because antigen tests look for a protein, rather than viral DNA, they are less sensitive than PCR tests. This means that an antigen test could be negative even if the person being tested has the disease.
There are currently other, more common causes of skin rashes that might result from sexual transmission, including herpes and syphilis. Due to the fact that many cases of monkeypox have resulted from sexual transmission, it is most likely that labs will use PCR tests to evaluate for multiple, potential causes of the patient’s illness. Given that the ongoing monkeypox outbreak has resulted in tens-of-thousands of cases across more than 80 countries, it is unlikely to be contained.
There is a growing possibility that monkeypox will become an endemic sexually transmitted infection that will need to be considered in patients with a rash-like illness following intimate exposure with a new partner. As the case count increases, new tests will likely be developed, including those that allow for an individual to collect their own specimen from home (but send that sample to a lab for testing), multiplex tests that analyze a specimen for several diseases (such as monkeypox, herpes, syphilis) in the same test, and potentially in the future, those that do not require samples to be submitted to a clinical laboratory. Hopefully, the lessons learned from Covid-19 will result in innovative testing options to curb the spread of monkeypox.
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