Amid Measles Outbreak, a Question of Contagiousness in Dallas-Fort Worth Area
What kind of virus is measles?
Measles belongs to a family of viruses called paramyxoviruses, which include over 75 other viruses that infect humans and animals. These infectious microbes include mumps — one of the viruses targeted in the MMR vaccine alongside measles — and respiratory syncytial virus, a common, contagious illness that causes cold-like symptoms.
Structurally, measles looks a lot like a coronavirus, it’s built of similar parts, said Benjamin Neuman, chief virologist for the Texas A&M Global Health Research Complex. So instead of a spiky round ball, you’ve got more of a long snake and it’s covered in the same sorts of little bumps.
Using these little bumps, called fusion proteins, measles enters white blood cells and makes copies of itself. As the white blood cells travel throughout the body, they inadvertently spread the viral particles to organs such as the lungs, liver and, in rare cases, the brain.
What’s particularly bad about the measles virus is that it damages or destroys a lot of our immune cells that maintain our immune memory, said Scott C. Weaver, director of the University of Texas Medical Branch’s Institute for Human Infections and Immunity.
Forgetting all the pathogens a body has encountered is called immune amnesia. This process has been studied in infected rhesus macaque monkeys that had measles replace all normal immune memory cells with those that only recognize it.
Other studies found measles reduces an unvaccinated child’s antibodies that recognize other viruses and bacteria by anywhere from 11% to 73%. Some statistical models found it could take two to three years after a measles infection to restore protective immune memory, putting a child (or unvaccinated adult) at risk for other viral infections or diseases they may have recovered from before.
What makes measles so transmissible?
Weakening the immune system is just part of measles’ contagion playbook. The virus can spread with remarkable efficiency when viral particles in an infected person’s nose and throat mucus become airborne through a cough, sneeze or even breathing. These viral particles can linger in the air for up to two hours, said Dr. Minji Kang, an assistant professor and infectious disease specialist at UT Southwestern Medical Center.
To describe how easily an infection like measles can jump from person to person, epidemiologists use a term called the basic reproductive number, or R0 (pronounced “R naught”), said Diana Cervantes, an associate professor of population and community health at the University of North Texas Health Science Center. It represents the average number of people an infected person can spread the disease to, assuming there’s no immunity to the disease in a community or population.
While R0 isn’t an innate biological characteristic of a pathogen — it can change depending on a number of factors — typically the higher the R0, the more contagious an infectious disease is.
For measles, one infected person can spread the virus to anywhere from 12 to 18 unvaccinated people, said Cervantes. This makes measles more transmissible than influenza and COVID-19, said Weaver of UTMB. Some estimates put the R0 between 1 and 2 for influenza and between 1.4 to 2.5 for COVID-19, as estimated initially by the World Health Organization. Some later studies, however, have suggested COVID-19’s R0 could be as high as 7.
Cervantes said factors that affect R0 include duration (or how long you’re exposed to an infectious person); opportunities for transmission (for example, if you’re interacting with one or more people); the probability of transmission for each opportunity; and a person’s underlying susceptibility to infection.
This is why vaccination is crucial to curbing the spread of measles: by creating a firewall of immunity, the virus is largely barred from infecting someone even if they were exposed, effectively lowering measles’ R0.
If there’s a measles case introduced and everyone is vaccinated or there’s a high vaccine rate, you’re going to see a smaller R0, Cervantes said.
The measles, mumps and rubella (MMR) vaccine is over 95% effective in preventing infection, and prevents the spread of the virus when more than 95% of people in a community are vaccinated — what’s known as herd immunity.
Fortunately, the vaccine for measles is a better vaccine than the influenza vaccines, Weaver said. The measles virus itself doesn’t change very fast over time, unlike influenza and coronaviruses. We don’t have to constantly make new forms of the vaccine to keep up with the virus’ evolution.
Public health officials such as Dr. Philip Huang, health authority for the Dallas County Health and Human Services, are recommending Dallas-Fort Worth residents get vaccinated if they haven’t already.
It’s a real easy solution, said Huang. If people just [check] their vaccine records and get up to date on the recommended vaccines, that’s all people need to do.
Conclusion:
The recent measles outbreak in West Texas has raised concerns about the contagiousness of the disease and its potential spread in the Dallas-Fort Worth area. Understanding the biology of measles and how it is transmitted is crucial in preventing its spread. Vaccination is the most effective way to prevent the spread of measles, and public health officials are urging residents to get vaccinated if they haven’t already.
FAQs:
Q: How contagious is measles?
A: Measles is highly contagious, with an R0 value of 12-18, making it more transmissible than influenza and COVID-19.
Q: How does measles spread?
A: Measles can spread through airborne transmission, sneezing, coughing, and even breathing, with viral particles lingering in the air for up to two hours.
Q: What is immune amnesia?
A: Immune amnesia is a condition where the body forgets all the pathogens it has encountered, making it vulnerable to new infections.
Q: How effective is the MMR vaccine?
A: The MMR vaccine is over 95% effective in preventing infection and preventing the spread of the virus when more than 95% of people in a community are vaccinated.
Q: What is herd immunity?
A: Herd immunity is when a community has a high enough vaccination rate to prevent the spread of a disease, protecting not only the vaccinated individuals but also those who are not immunocompetent.
Q: Why is vaccination important?
A: Vaccination is crucial in preventing the spread of measles and other diseases, creating a firewall of immunity that protects individuals and communities.
