Chikungunya: Ebola pushes South American epidemic out of the spotlight
The debilitating mosquito-borne Chikungunya virus has infected almost one million people since it first emerged in South America and the Caribbean less than a year ago. The virus has rapidly spread across the Americas, causing huge pressure on health services in some of the poorest countries in the western hemisphere.
The Dominican Republic, the most popular Caribbean island for tourists last year with 4.7 million visitors, has recorded 500,000 cases. A third of the population lives on 80 pence ($1.25) a day. Central America has also been affected, with 123,000 cases in El Salvador.
The epidemic has failed to attract international media attention amid the Ebola crisis, as deaths from Chikungunya are relatively rare: . About 150 people have died among nearly 931,000 cases in the Americas – the US has had more than 1,830 cases.
But Chikungunya causes painful and debilitating symptoms in more than 80% of those infected, and can exacerbate poverty due to missed work and medical expenses (pdf).
Patients most commonly suffer painful and swollen joints, fever, headache, fatigue and a rash within three to seven days after an infected bite. The symptoms usually disappear within three weeks. However, arthritis, especially in the wrists and hands, can last for months, or years in some people, causing long-term disabilities. “Chikungunya” means “bent over” in the Makonde language of Tanzania, where the virus was first detected in 1952, and describes the stooped appearance of those with joint pain.
The virus can also cause diarrhoea and vomiting, mouth ulcers, visual problems and meningitis, which pose the greatest threat to vulnerable groups including elderly people, babies, pregnant women and those with existing conditions such as high blood pressure or diabetes, according to the Pan American Health Organisation, which is monitoring the epidemic. There is no treatment or vaccine and the first human clinical trials are at least several years away.
“[Chikungunya] has clearly become a global virus,” said Dr Alain Kohl, head of the University of Glasgow Centre for Virus Research, where scientists recently made an important breakthrough in preventing transmission.
He added: “Short-term infections that affect large numbers of people can have a very significant impact on the economy and health services, and long-term issues such as arthritis that are associated with Chikungunya can very badly affect patients. Public health impact is not just a measure of death rates.”
Chikungunya is spread by two particularly aggressive mosquito species – Aedes aegypti and Aedes albopictus – which bite during daylight hours, breed in stagnant water and favour biting humans. These mosquitoes, which also spread dengue and west Nile fever, are recognised by the white stripes around their legs.
But humans are key to transmission. A mosquito only becomes a carrier by biting an infected human, such as a holidaymaker returning home. Chikungunya cannot normally be transmitted from one person to another, although a few cases of mother to baby transmission have been reported.
Dr Jean Staples, epidemiologist and arboviral disease expert at the US Centers for Disease Control and Prevention, told the Guardian: “With viruses like Chikungunya, dengue and even Ebola, where people are a main route of transmission, globalisation and international travel definitely impacts on the spread.”
The first locally transmitted cases of the virus in the western hemisphere were detected last December on Saint Martin.
It rapidly spread as the virus is new to the Americas, which means it is attacking people with no immunity against it. The mosquitoes responsible thrive in the region’s tropical wet and warm climate. Chikungunya, which is more debilitating than dengue, is also easier to spread as sufferers are infectious for much longer.
Small outbreaks in France, Italy and, most recently Florida, have been contained by well-planned and well-resourced public health responses. This is much harder for countries like the Dominican Republic, Haiti and El Salvador where health services are already strained.
This epidemic is not unprecedented. In 2005-06, a third of people on the French La Reunion Island were infected over a few months – 266,000 of 785,000 habitants – in an outbreak that originated in Kenya. This led to millions of cases in India, Europe and across the Indian Ocean over the next two years.
Dr Laith Yakob, who studies the links between human-induced environmental changes and infectious diseases at London School of Hygiene and Tropical Medicine, told the Guardian that “globalisation through massively increased international travel” helps viruses migrate.
“There is also a tendency for the most connected places on Earth to have very large human populations, providing excellent opportunities for newly introduced pathogens to successfully invade,” he added.
It’s too early to predict the final human and economic costs of the epidemic, but he 2005-06 outbreak cost La Reunion £35m – 60% in direct medical costs.
It is unclear whether Chikungunya will become endemic in the Americas, and therefore another long-term drain on economies and health services. It has in India, but not in La Reunion. “It will depend on the virus’s ability to find a niche in non-human primates to sustain it and keep it circulating; only time will tell,” Staples said.