Tuesday was World Mosquito Day, so for this week’s Outbreak Thursday post, we thought we would highlight one of the many pathogens that these insects can spread: Chikungunya virus. The arbovirus, which is often grouped with the Zika and Dengue viruses (thanks to those pesky Aedes mosquitoes), has been mentioned in previous Outbreak Thursday posts, but hasn’t received a spotlight detailing its impact on global populations.
The What and Where of Chikungunya
The post referenced above gives a thorough background of the signs, symptoms, transmission, and history of the Chikungunya virus. To briefly summarize, Chikungunya is a tropical virus that can be spread through the bite of either Aedes aegypti or Aedes albopictus mosquitoes. Symptoms of the virus are often painful, but rarely result in death. There is currently no vaccine or therapeutic designed to address Chikungunya, but evidence suggests that those who have already had the disease will have life-long immunity.
In theory, Chikungunya can be found wherever either Aedes mosquito is present, but the highest number of cases are tied to areas with tropical climates due to heightened mosquito activity. Reported cases have come from around the globe, with every continent (sans Antarctica) experiencing at least a handful of cases over the last five years. The range of these mosquitoes is dynamic, and there are concerns of a drastic expansion due to the planet’s increasingly warming climate.
The remainder of this post will move region by region to highlight some of the on-going global outbreaks of Chikungunya.
According to the ECDC two countries within the African region had reported outbreaks of Chikungunya by the end of June 2019: the Republic of Congo and the Democratic Republic of Congo (DRC). The Republic of Congo has seen over 11,000 cases of Chikungunya during an ongoing outbreak that began in February, although cases are now on the decline. The Congo has implemented traditional methods to support vector control, and additional research has been completed to determine the proximity of the current outbreak strain to other preexisting strains circulating Central Africa. The outbreak in the DRC is smaller, with just over 800 cases reported between the start of the year and the middle of April.
Separate from the ECDC listing, there have been additional reports of outbreaks in Sudan and Ethiopia. The Sudanese government reported in February that there had been roughly 10,000 cases of Chikungunya over the previous four months. These cases were mainly isolated within the countries Red Sea state, and some believe they were tied to flooding earlier in the year. While these numbers subsided over the county’s winter, recent reports show 73 new cases in the same district. In Ethiopia, there have been reports of roughly 4,000 Chikungunya cases tied to an ongoing outbreak in Dire Dawa.
The ECDC last updated their list of ongoing Chikungunya outbreaks at the end of June. In that report, they listed that outbreaks were occurring in the following countries: India, Indonesia, the Maldives, and Thailand. According to this report, India has only seen 250 cases of Chikungunya between the start of the year and the end of April, and Indonesia has only 17 cases in that same time period.
The Maldives have had over 1200 cases of Chikungunya between the beginning of this year and the middle of June. This is particularly notable since the country has not reported an outbreak of the virus in 13 years. According to reports, the Maldives have also had a particularly bad year with Dengue fever, and they are undergoing efforts to try and control the mosquito population. A national vector control campaign was announced in April of this year and included activities ranging from community education to the removal of mosquito breeding areas.
Thailand has also seen a drastic increase in the number of Chikungunya cases between this year and last. As of earlier this week, the total number of Chikungunya cases in Thailand was approaching 6000. This was a leap from the month before where roughly 4500 cases were reported. According to ECDC Thailand only reported 34 cases of Chikungunya last year, adding to global concern over the rise of tropical, mosquito-borne disease.
The following Central American countries have reported cases of Chikungunya this year: El Salvador, Honduras, and Nicaragua. Although reporting over slightly different time periods, each of the countries have seen less than 250 cases total, but each have seen increases in comparison to the number of cases at the same point in time last year.
The United States has seen 0 cases of locally transmitted Chikungunya this year, but has had 40 travel-associated cases. In 2014, the continental United States had 14 locally-transmitted cases of Chikungunya, but has only had one such case in the following five years.
In South America, Columbia, Peru, and Paraguay had each reported under 1000 cases of Chikungunya for the year. On the contrary, Brazil has received a large amount of media attention due to an outbreak that has grown to just under 100,000 cases as of the end of July. In July, a Brazilian news source shared that the state of Rio de Janeiro, which includes the major metropolitan center and surrounding areas, accounted for the largest portion of cases (approximately 60,000). Chikungunya virus was first identified in the Americas in 2013, and in the following years has had firm presence in Brazil, especially in Rio de Janeiro. In June of 2017, scientists from the Oswaldo Cruz Institute published a research paper illustrating the high risk for the Chikungunya virus to establish an enzootic sylvatic cycle in Brazil. An enzootic sylvatic cycle describes how a pathogen interacts with animal hosts in a natural environment, and establishing such a system increases the chance of Chikungunya becoming an endemic threat for years to come.
Chikungunya: What Comes Next
Chikungunya, and other arboviruses, are posed to be a sizeable threat in the coming years. However, there are several opportunities for the global public health community to mitigate the impact of this virus. While there are still no vaccines or treatments currently available to prevent/treat Chikungunya, there are ongoing efforts to build this capacity. In the later weeks of June, the Coalition for Epidemic Preparedness Innovations (CEPI) announced that they had granted an award of over US$20 to support Valneva’s late-stage Chikungunya vaccine. In addition to medical interventions, there are a number of non-pharmaceutical interventions that could help reduce the spread of the virus. For example, community education efforts designed to reduce breeding grounds of mosquitoes could have a beneficial effect, limiting not only Chikungunya, but other arboviruses as well. The opportunity to advocate for improved global mosquito control cannot be overlooked, especially in an increasingly connected world with a growing range of mosquito-friendly climates.
Photo courtesy of Dr. Pratt., retrieved on the CDC’s Public Health Image Library
Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.