Hopkins Professor Discusses Measles, Vaccines and Infectious Disease Course
With fears about measles outbreaks spreading throughout our country, Hopkins Happenings interviewed Gregory Stewart, an adjunct professor for JHU’s Advanced Academic Programs Biotechnology Department. Stewart has taught microbiology, molecular biology and biochemistry at the university level for more than 20 years. He currently teaches Microbiology and Infectious Diseases at the Montgomery County Campus in the evenings. During the day, he is a senior scientist for Tetracore, a Rockville-based biotechnology company focusing on human and animal pathogens.
Hopkins Happenings: Describe your infectious diseases class. What topics do you discuss? What do you hope students learn from the course?
Stewart: My approach to the Infectious Diseases course is a mechanisms of pathogenesis approach. We focus on those aspects of the genetics and biochemistry that allow pathogens to cause disease and its symptoms in human hosts, and we work to understand the mechanisms the human host uses to fight off infection. We study the specific "virulence factors" that make a pathogen a pathogen, and how they are genetically encoded, regulated and expressed. We also look at their mechanisms of action.
My approach teaches students to look for the "tools" the pathogens use. As a result, when students see these tools in new pathogens, they have a basis for understanding the consequence of the new pathogen in a human host. We also study the presence and consequence of "pathogenicity islands,” clusters of genes that encode virulence factors and that can move horizontally between different bacteria. This is important in understanding the spread of antibiotic resistance in pathogenic bacteria.
Hopkins Happenings: What is measles?
Stewart: Measles is a viral disease also called "rubeola.” It is an extremely contagious disease that is endemic throughout the world. The virus causing measles is a negative strand enveloped RNA virus of the genus Morbillivvirus. The disease is spread through inhalation in the respiratory tract or through the conjunctiva of the eye. Negative strand means that when the RNA enters host cells, those cells must first convert the virus to double stranded RNA to make a positive RNA strand that can be expressed. The envelope of the virus assists in the infection process.
After infection, the host will carry the virus without expressing symptoms for 10-14 days. Around the tenth day, symptoms begin, including nasal discharge, cough, fever, headache and conjunctivitis. The disease progresses in the intensity of these symptoms as the characteristic rash and small red bumps that eventually cover the whole body. These lesions are also sometimes found in the mouth. While there is no treatment, a vaccine that is part of the childhood MMR vaccination prevents the disease in most cases.
Hopkins Happenings: How will you approach the topic of measles in your class?
Stewart: In the Infectious Disease class we will discuss the viral-encoded proteins that contribute to the virulence of the virus. We will look at the frequencies of measles prior to the development of the MMR vaccine and the frequency of the disease in the United States after this vaccine became required for admission to public schools. We will discuss the recent social movement among some parents to opt out of vaccinating their children and the resurgence of measles in the U.S. that has resulted as a consequence. We will study the mechanism of transmission of the disease as well as the elements that control its spread.
Hopkins Happenings: Why is a measles outbreak hard to stop? How does it spread? What can be done to stop measles from becoming a widespread public health crisis?
Stewart: While we managed to reduce the frequency of measles in the United States in recent years through mass vaccination, the disease is endemic throughout the world where vaccination is not practiced. As international travel has increased, so has the potential for re-introducing the virus to the U. S. population. The virus is spread through water droplets that are expelled by infected hosts through coughing or through nasal secretions. The virus is sufficiently tough to allow it to survive for some period of time on inanimate objects, such as door knobs and drinking glasses. The best protection from the virus is either previous exposure (our immune system raises antibodies against the virus after an initial case of measles) or through vaccination. Widespread vaccination reduces the pool of potential hosts that can become infected. This provides some degree of protection to the unvaccinated population through a process called herd immunity.
Hopkins Happenings: How was the measles vaccine developed? What are the possible consequences of failing to vaccinate?
Stewart: The measles component of the MMR vaccine (Measles, Mumps, Rubella) incorporates a weakened measles virus that does not result in full blown disease but activates the immune system, providing protection from the virus upon future exposures. Attenuated viruses are produced by serially cultivating the viruses in tissue culture cells that are poor hosts for the virus. After several transfers through these cell cultures, the virus loses its ability to cause full-blown disease in the human host.
Given the effectiveness of the MMR vaccine, why do some parents elect not to vaccinate their children? Many years ago a paper was published that implied a causative connection between the MMR vaccine and autism in vaccinated children. Although this study has been debunked multiple times, there are organizations that still proliferate this misinformation. As a result, these parents will risk their children acquiring measles, mumps, and rubella (and exposing others to the disease). While rare, deaths can result from these diseases, thus, failure to vaccinate one's children can result in serious illness or death.