PHILADELPHIA — The biggest viral disease outbreak has nothing to do with Ebola. It is Chikungunya virus, and it is sweeping the Americas. The primary symptoms are fever and polyarthralgia. "Chikungunya, in the Makonde language of Tanzania and northern Mozambique, means that which bends over or dries up," said Lyle Petersen, MD, from the US Centers for Disease Control and Prevention (CDC) in Fort Collins, Colorado.
Unlike the Dengue virus, where most infections are asymptomatic, 72% to 97% of people infected with the Chikungunya virus develop clinical symptoms. The incubation period is usually 3 to 7 days, with a range of 1 to 12 days, Dr Petersen reported here at IDWeek 2014.
The reason people bend over is that their joints hurt so bad they cannot walk. The arthralgia is often severe and debilitating, usually bilateral and symmetric, and is most common in the hands and feet. The onset of fever, typically greater than 39 °C, is abrupt. Patients can also experience headache, myalgia, nausea, vomiting, maculopapular rash, and arthritis.
The acute symptoms usually resolve in 7 to 10 days, but some patients have a relapse of joint pain and tenosynovitis in the subsequent months. "Studies report variable proportions of patients with persistent joint pain for months and years," Dr Petersen said. Mortality is rare, but if death occurs, it is usually in older patients with underlying conditions.
Chikungunya is a mosquito-borne single-stranded RNA virus with 3 major genotypes: West African, East/Central/South African, and Asian. There is sylvatic transmission in forested regions of Africa, probably involving nonhuman primates, but in the urban setting, transmission is similar to that of Dengue. It is direct human, mosquito, human transmission, and the vectors are Aedes aegypti and Aedes albopictus.
Human, Mosquito, Human Transmission
Outbreaks that in retrospect sound like Chikungunya have occurred since the 1700s, but the virus was initially described in a febrile woman in Tanzania in 1953. Since then, numerous outbreaks have occurred in India, Southeast Asia, Africa, islands off Africa, and in the Indian Ocean. Vacationers in the islands then brought Chikungunya back to Italy and France.
The virus picked up the E1-A226V mutation, which increases its fitness in A albopictus, a species that can live in more northerly climates than A aegypti. A aegypti is a better vector because it bites people in their houses and often bites multiple people, but A albopictus now has a range extending as far north in the United States as Pennsylvania, Ohio, Illinois, and as far west as Texas and Kansas. This broader range of A albopictus "increases the distribution of outbreak potential in the United States," Dr Petersen showed.
The first cases on the island of St. Martin in the Caribbean were reported in 2013. Oddly, the virus was of the Asian genotype, which lacks the E1-A226V mutation. Outbreaks quickly spread from island to island and then to South America. By July 2014, Chikungunya reached mainland United States.
As of September, it was in 37 countries in the Americas and had caused 751,752 reported cases and 118 deaths. "This is really a high morbidity, low mortality disease," Dr Petersen said.
To date, 46 states have reported Chikungunya cases (11 locally acquired and 1326 travel-associated). Of those, 18% were in Florida and 25% were in New York. Chikungunya is not yet a reportable disease, but it will be soon. "If you have cases, please report them," Dr Petersen urged.
More than 10,000 locally acquired cases — probably an underestimate — have been reported in Puerto Rico, and almost 900 have been reported in the US Virgin Islands.
"Unlike your stock portfolio, where past performance does not equal future results," he explained, "past performance is going to equal future results here."
He said that in his opinion (not that of the CDC), "explosive, large outbreaks in tropical America will continue for several years until large proportions of the population become immune." He expects to see "millions or tens of millions of cases" in these outbreaks, and tens of thousands of travel-associated cases will be seen in the continental United States. Sporadic, locally acquired cases might occur, but the outbreak potential in the United States will be somewhat limited.
Dengue vs Chikungunya
Dengue cases could also be brought into the country, and differentiating the two diseases might not be easy. The biggest difference will likely be in the pattern of pain. Whereas Dengue patients can hurt all over, Chikungunya will probably affect hands and feet.
A laboratory diagnosis can be made with real-time polymerase chain reaction or IgM antibody tests.
There is no specific antiviral therapy for Chikungunya, but supportive care with rest and fluids is recommended, with nonsteroidal anti-inflammatory drugs (NSAIDs) for acute fever and pain. NSAIDs, corticosteroids, and physiotherapy can help with persistent joint pain, although there is a lack of data in this area.
"The thing that really should strike people is the magnitude of the outbreak," said session moderator Ravi Jhaveri, MD, associate professor of pediatrics at the University of North Carolina School of Medicine in Chapel Hill, and IDWeek program committee vice-chair. We're talking about 750,000 cases, "and that's an underestimate for the Americas," he told Medscape Medical News.
He said Dr Petersen put the problem into perspective, citing 7000 confirmed cases of Ebola and the attention that it is getting. "As ID physicians, we're far more likely to encounter a patient with Chikungunya at this point than we are Ebola," Dr Jhaveri pointed out.
He said infectious disease physicians can help guide community practitioners in their thinking about the disease. For example, they can advise community practitioners to ask patients about travel and other risk factors, and then to consider diseases like Chikungunya or Dengue.
Dr Petersen and Dr Jhaveri have disclosed no relevant financial relationships.
IDWeek 2014: Presentation 20C. Presented October 8, 2014.
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