Chikungunya and new strains of influenza are among a list of emerging infectious diseases that have grabbed recent headlines, but reemerging diseases including measles and pertussis are also causing epidemiologists concern across the nation.
“There are newly emerging diseases and reemerging diseases … and both are disturbing,” stated Tim Jones, MD, state epidemiologist for the Tennessee Department of Health (TDH). Jones, whose past experience includes working in the Centers for Disease Control and Prevention’s Epidemic Intelligence Services, recently provided insight into the old and new. He also shared his thoughts on why we’re seeing a resurgence of some diseases, such as polio, that the medical community thought would be a distant memory at this point in history.
“Internationally, we had hoped that polio would be eradicated by the turn of the century, but here we are in 2014 with it expanding into additional countries,” he said.
Jones, who is the immediate past president of the Council of State and Territorial Epidemiologists, noted the spread of new diseases and return of some of the older ones is multifactorial with global mobility and increasing refusals to be vaccinated contributing to the problem.
Emerging Infectious Disease
“The majority of these new diseases are what we call zoonotic. As the name suggests, they are diseases that have jumped from the animal world into humans,” Jones explained, adding examples include SARS, West Nile Virus and H1N1.
The most recent mosquito-borne disease to make its way to the United States is chikungunya. “We just started seeing it in the last few months,” Jones noted of the disease’s migration primarily from the Caribbean where there have been large outbreaks. “Our first cases in Tennessee were in May. We’d never seen it before. As of today, there are 37 suspected cases, and all of them are people who have recently returned from the Caribbean.”
Jones added, “This new one, chikungunya, luckily does not have a reservoir out in the wild.” He explained the viral disease doesn’t live in birds or other animals and only transmits between mosquitos and humans. “For me to get it, the mosquito would have to bite an infected person and then me. So far we haven’t seen any jump from infected travelers to someone local, but that’s what we’re afraid of.”
(Editor’s Note: At the time of the interview in early July, there had not been any cases of chikungunya originating in the United States. However, the CDC has since confirmed the first cases of the virus being locally acquired. The virus is transmitted through two species of mosquitoes, Aedes aegypti and Aedes albopictus, which are found in a number of regions across the country including the Southeast.)
Primary symptoms include joint pain and fever. Although there is no vaccine, Jones noted, “It’s rarely fatal, but it makes you feel terrible for about a week, and 10 to 15 percent of people will have very bad arthralgias for up to a year.”
Dengue is another mosquito-borne virus that epidemiologists are closely monitoring. “Generally, it’s pretty endemic in the Caribbean and South and Central America, but it seems to be moving north,” Jones said. “As these vector-borne diseases move into new areas, it raises concerns as to whether it could be related to climate change.”
With no vaccine or treatment, dengue is a leading cause of illness and death in the tropics and subtropics and is caused by any of four related viruses transmitted by mosquitos. “Unfortunately, dengue you can get more than once, and if you get it a second time, it’s usually much more severe,” Jones said, adding it’s nickname is ‘breakbone fever’ because the intense joint and muscle pain can cause those with dengue to have contortions.
The first 2014 human case of yet another mosquito-borne disease, West Nile Virus, was confirmed in Tennessee in late June. WNV has been present in the state since 2001.
The common thread with all three of these viruses is that there is no vaccine so prevention remains the best way to contain the spread of the virus. The TDH lists a number of recommendations on their website for individuals to prevent mosquito bites including the use of insect repellants and elimination of standing water near homes.
Reemerging Diseases
Although ‘officially’ eradicated from the United States in 2000, measles is still present in other regions of the world and has begun to reappear in this country. In fact, the CDC recently announced they have confirmed more cases of measles in the United States so far in 2014 than in any other year in the past two decades.
This spring, the TDH identified the first case of measles in the state in three years. As with most cases now seen in this country, the virus was traced to an international traveler and then spread to those who weren’t immune to the disease.
“We had one person who returned from overseas from an area that was having an outbreak, and we ended up having five people infected before we got it under control,” Jones said. Transmittable through the air, he added, “Measles is very serious and really, really easy to spread.”
Although the state has a very high rate of compliance for the measles vaccine, Jones pointed out that the vaccine was really only recommended for those born after 1957 since many older citizens were exposed to measles in childhood. A two-part vaccine, Jones said the state probably only has 2-3 percent of the population that isn’t fully immunized.
Pertussis, or whooping cough, is another disease spreading throughout the country. Although Jones said Tennessee has only had light activity with 100-200 cases per year, other parts of the country have been much more heavily affected. “There are some states in the Midwest and now California that have had many hundreds and thousands.”
The problem, Jones continued is a combination of under-immunization and the fact that it isn’t a perfect vaccine. Because of some concern about the immunization wearing off, a booster is now recommended. “In the last couple of years, we began recommending all adults that haven’t had this new Tdap (tetanus, diphtheria and acellular pertussis) vaccine get a dose no matter when the last time they had a tetanus shot,” Jones said.
In Tennessee, the continuing concern over tuberculosis comes with some good news and some bad news. “For the first time this year, Tennessee is below the national average, which is exciting … but as the numbers go down, the complexity of each case is going up,” Jones said.
He added, “While we’re having a real impact on domestic TB, now nationally the majority of TB cases are in the foreign-born population. We’re seeing much more imported TB.”
Although contagious, Jones said it takes close, prolonged contact rather than casual proximity to spread the disease. In the absence of a good vaccine for TB, testing becomes important … particularly for healthcare workers.
A major issue with reemerging diseases is a lack of recognition by healthcare providers since they are so rare. “There are very few physicians in the U.S. who have ever seen a true case of measles,” Jones said. “Likewise for TB … most physicians are never going to have seen a real case, and that makes it challenging.” He added, “With TB, for example, we’re increasingly seeing people who went to a healthcare professional and were treated for bronchitis, smoker’s cough, etc. We’ve got to keep these diseases in the back of our minds as possibilities.”
Jones said education and awareness are key to catching infectious diseases early. The CDC has extensive information on both emerging and reemerging public health threats. Likewise, the TDH provides resources and local updates about diseases present in Tennessee. For more information, go online to cdc.gov and to the TDH section on communicable and environmental diseases and emergency preparedness (CEDS) at health.state.tn.us/ceds.
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