AMG BACKGROUNDER
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BY DEBORAH ALMOND — As the Dominican Ministry of Health officially declares their Chikungunya (CHIKV) epidemic over, we take a look at five badly affected countries in the region and where they stand now.
Dominica
Since Dominica’s first confirmed case in January 2014, CHIKV has swept across the island of 72,000 infecting at least 3,771. The announcement on January 23 that the epidemic is now over comes a year after one resident returned from a trip to Saint Martin, bringing the virus with them.
World Health Organisation guidelines recommend an epidemic can be declared over after two maximum incubation periods have passed without a new case being reported. Dominica has long surpassed the 24 days required to reach that criteria with 50 days without a diagnosis.
Chief Medical Officer Dr. David Johnson has urged caution despite the good news, reminding people that this does not mean CHIKV has been eradicated from Dominica.
During a press gathering last week, he reminded the public that, “not everybody who had chikungunya reported to the health care facility, some persons treated themselves at home. When the disease was established, persons knew what they had, and some persons did not report it.” It is possible this pattern of behavior continues, meaning others may have been infected since the epidemic was declared over but have chosen not to visit a doctor.
Dominican Republic
Much like in Dominica, the Dominican Republic experienced a steep rise in cases through the summer months of last year. Their population of 10,415,000 has led to far greater numbers of cases in comparison to other Caribbean countries, with over half a million becoming infected.
The actual number is likely to surpass this as many do not seek formal medical attention, relying instead on advice from their local pharmacies. Regular confusion between CHIKV and Dengue Fever – a familiar infection in the country – may have also led to misdiagnosis and inaccurate reporting.
One of the mosquitoes that transmits CHIKV, called Ae. aegypti, is present here in large numbers making the Dominican Republic fertile ground for an epidemic. This breed is closely associated with human habitation and indoor breeding sites, like the large bottles many use to contain drinking water in their homes.
The frequency of new cases appears to be tapering now that over 5% of the population has been infected. The population difference is one reason it will take the Dominican Republic longer than Dominica to declare an end to its epidemic. Others include poor access to health care for those at most risk and a higher number of untreated mosquito breeding sites in and around homes.
Neighbouring Haiti has so far reported over 64,700 cases, although this may be a conservative estimate. Due to Haiti’s lower levels of infrastructure and development and its population density of 374 people per km2, they are likely suffering similar numbers of infection.
Saint Martin
Saint Martin, with a population of fewer than 75,000, was the epicenter of this epidemic. In December 2013, 2 laboratory-confirmed non-imported cases were reported for the first time in the Caribbean in the district of Ocean Pond, close to the border of the Dutch side Sint Maarten.
Following genetic tests carried out in France, the strain of virus was found to be related to those recently identified in Indonesia (2007), China (2012) and the Philippines (2013). Several states in India had reported a rise in CHIKV cases during 2013, signifying a possible link to the substantial Indian community in Saint Martin.
The number of new cases rose steeply between February and April last year (Graph 1), and continues to do so into 2015. Despite improved surveillance and collaboration with Sint Maarten, residents remain at increased risk. This is in contrast to their Dutch neighbours who have a rate of new infection per population almost fifteen times lower.
Martinique
Of the 50 affected countries across Latin America and the Caribbean, Martinique’s epidemic has claimed the most lives. Since December 2013, at least 73,715 have been infected and 83 people have died. The Pan American Health Organization has said that it is not clear whether or not these deaths can be directly attributed to the virus, only that it has been recorded as a contributing factor.
A steady rise of infection can be seen (Graph 3) throughout 2014 with what appears to be a levelling off of new cases since the beginning of this year.
St. Barthélemy
The worst affected island per population has seen a fifth of its residents infected since December 2013, and continues to see a rise in cases (Graph 1). As with the rest of the Caribbean, residents of St Barthélemy had never encountered the virus before and had no existing immunity. Providing CHIKV remains in its current form, those who have been infected should now have lifelong resistance.
Despite this, joint pain can persist for months or even years after other symptoms have subsided affecting some people’s daily routines and mobility. No vaccine has yet been developed to prevent infection and those dealing with continued discomfort are left with only analgesics until improved therapeutic gains are made.
While in some islands the epidemic is beginning to wane, the rest will have to rely on the government prescribed control methods of avoiding mosquito bites and reducing their breeding sites.
Other AMG products on Chikungunya:
Tracking Chikungunya across the Caribbean
Chikungunya in the Caribbean: A Backgrounder for Non-specialists
New strain of Chikungunya in Brazil could spur North American outbreak
All epidemiological information from PAHO and WHO’s weekly fact sheet ‘Number of Reported Cases of Chikungunya Fever in the Americas, by Country or Territory.’
