Annual Meeting Reviews
Session IV: Emerging Pathogens
By Elizabeth S. Yun, MD
University of Wisconsin School of Medicine
Madison, WI
David Weber MD, Professor of Epidemiology, Medicine, and Pediatrics (University of North Carolina) presented the lecture: Emerging Viral Pathogens. In this talk he reviewed the driving factors behind emerging infections, the epidemiology and clinical features of specific diseases, and key issues critical to controlling the spread of these diseases.
An emerging infectious disease is defined as an infection that has newly appeared in the population or has previously existed but is now rapidly increasing in incidence or geographic range. Disease emergence is complex and dynamic. Most new infections are not due to new pathogens and the idea of a microbe as the cause of a disease is now inadequate. These infections cross over taxonomic lines from animals to humans. Human activities including social, climatic, economic, and political conditions are the most potent factors driving disease emergence.
The most important factor is the increased speed of global travel. For example, in the United States, almost 70 million people visit from all over the world with an increasing number coming from emerging economies. These visitors are potential carriers of various emerging pathogens. Due to these factors, understanding and responding to new disease emergence requires a global perspective. There has to be knowledge of the geographic location, incubation period, clinical features, diagnosis, and therapy of the disease. With these facts, the clinicians need to quickly screen and diagnosis patients. To control the spread of infection, there needs to understanding of communicability and transmission routes, environmental survival, susceptibility to germicide, and post exposure prophylaxis.
Dr. Weber described several important emerging pathogens that have recently appeared or reappeared in the United States. He started with measles. Measles is a single stranded enveloped RNA virus with an incubation period of 7-21 days. Its characteristic symptoms are conjunctivitis, pathognomic Koplik spots, and an all body maculopapular rash, along with high fever and cough. Diagnosis is confirmed with lab testing. It is also a highly contagious airborne disease that can survive for over an hour after the source has left an enclosed area. Because of an effective vaccine, the US declared that measles was completely eliminated. However in 2015, outside sources imported the disease to California and started a measles outbreak in mainly unvaccinated or status unknown patients.
Mumps is another highly contagious disease that has been associated with several large outbreaks from 2006-2013, mainly in college aged students living in close contact. It is a single stranded RNA virus easily transmitted through droplets. It has an incubation period of 16-18 days. The prodromal symptoms are nonspecific: low grade fever, myalgia, anorexia, and headache. The classic sign is a parotitis in one or both parotid glands. Because of the nonspecific nature of the symptoms, mumps is often mistaken for other diseases of the lymph nodes.
Dr. Weber reviewed the current Advisory Committee on Immunization Practices that can be found on http://www.cdc.gov/vaccines/acip. He noted that for health care professionals, proof of immunity is now based on serological testing and not on a doctor’s diagnosis or self report as it had been in the past.
Dr. Weber also discussed several pathogens originating in other countries that are now appearing in the United States. Dengue is a single positive stranded RNA virus that is transmitted to humans via the mosquito. It has an incubation period of 3-14 days and is characterized by acute onset of high fever, frontal headache, retro-orbital pain, myalgias, arthralgias, rash and hemorrhagic manifestations. While most US citizens with dengue fever live in Puerto Rico, US Virgin Islands, Samoa, or Guam, recently there have been outbreaks in Texas, Hawaii, and Key West. With climate changes affecting the mosquito population, there is concern that cases of dengue may arise in new locations in the United States.
Enterovirus D68 is a non-polio enterovirus first identified in California in 1962. It is transmitted by droplet and contact and causes a respiratory illness. In 2014, there was a large outbreak in the United States with most cases occurring in children, especially those with asthma history. Because of its nonspecific symptoms, it may be undiagnosed in many people.
Chikungunya is a single positive sense stranded RNA virus also spread by mosquitos. It has an incubation period of 3-7 days and is characterized by acute onset of high fever and polyarthralgia that resolve in 7-10 days. Because of these nonspecific symptoms, diagnosis is difficult. Complications are sever and include myocarditis, uveitis, hepatitis and nephritis. Persons at risks included neonates exposed intrapartum, adults greater than 65 years or with other comorbidities. This disease was widespread in Africa, Asia and Europe. The few cases that occurred in the United Stated were in travelers from other countries. However since 2014, local transmission was reported in Florida, Puerto Rico and US Virgin Islands.
SARS is an example of a coronavirus that spread throughout Asia from one person who infected over 8000 people. 775 deaths occurred from SARS with health care workers making up about 21% of the deaths. However the spread was controlled with international cooperation and good public health care. SARS is transmitted from animal to human or human to human via aerosol contact. It has an incubation period of 2-14 days, low communicability, but a long environmental survival. It is susceptible to common germicides. The SARS epidemic highlighted several important lessons in infection control. There needs to be an initial detection by an acute observer and then rapid diagnosis. The epidemic has to be contained with quarantine and other infection control methods. Response to an epidemic needs to be part of every hospital’s disaster plan and has to be implemented quickly. Travelers need to be screened at the entry of a hospital or clinic. Adequate protective equipment must be provided to hospital workers who are at high risk of getting the disease
MERS is a pathogen similar to SARS in several ways. MERS is a coronavirus that has an incubation period of 2-15 days. Transmission is also animal to human or person to person via aerosol. It also has low communicability, long environmental survival and susceptibility to germicides. Like SARS, the most recent outbreak that occurred in the Republic of Korea was traced to one person who had recently travelled to the Middle East and was not diagnosed immediately. MERS infected about 172 cases with 27 deaths, thus having a higher mortality rate to SARS.
Ebola is the latest viral pathogen to cause a large outbreak, especially in Sierra Leone, Guinea and Liberia. The Ebola epidemic highlighted the initial problems with infection control. There was a lack of government funding. Experts disagreed with the CDC recommendations, leading to confusion about protective equipment and incubation time. There were inadequate facilities for patient care, inadequate personnel protective equipment and point of care lab equipment. While the outbreak has been contained it is still an ongoing epidemic. The greatest concern with Ebola is that it is slowly incubating beyond the 21 day period and replicating in hidden parts of the body (ex. CSF, semen) and leading to a recrudescence many months later or new transmission ways to humans (ex. sexual). This new finding highlights the need to find a new way to control the spread of Ebola.
The final pathogen reviewed was Influenza. The nomenclature provides a description of each strain. There are three virus types, A, B, C with A being the most virulent. The subtypes of Influenza are defined by the virulence factors hemaglutinin and neuraminidase. There are 18 hemaglutinin subtypes and 11 neuraminidase subtypes and together they create 200 types of Influenza A. For unknown reasons there have been shifts in the types of Influenza A over the years. Recently, two different circulating strains, H1N1 and H3N2 were present at the same time for unknown reasons. In 2009, the H1N1 shifted to a new pandemic H1N1 strain with limited immunity. Many planning assumptions were created to deal with this pandemic, with mixed results.
The pandemic strain was not H5N1 from Asia as initially assumed, and mitigation strategies of vaccines and social distancing did not work. Children turned out to be the vector for this infection since they have low susceptibility, and shed higher amounts of the virus for a longer period of time and cannot control their secretions. The elderly did not have the highest morbidity and mortality since they might have had some protective immunity from previous vaccinations and exposure to earlier pandemics. The largest group of deaths occurred in 15-25 year range. While there were a large number of infected people, the number hospitalized was low thus showing that infectivity and virulence are two different attributes of this virus. Asymptomatic persons still transmitted the disease. Antivirals are plentiful; however vaccines are not available for 6 months with current technology.
Globally there are many novel strains of Influenza A. These viruses cause scattered cases of highly virulent avian flu that lead to high mortality in birds but have low communicability with humans. However it is possible that one of these novel strains could be transmitted to a human with H1N1 where it could recombine to produce a highly transmissible virus that could produce a pandemic.
