Fourteen confirmed cases of chikungunya in Italy—6 from Rome and 8 from the coastal area of Anzio—have been reported by the WHO regional office in Europe, with more potential cases under investigation. What is particularly important is that these cases were likely acquired locally, rather than during overseas travel. The occurrence of local transmission of chikungunya in Italy is not surprising—the country has previously experienced local outbreaks of the disease—but the newly reported cases illustrate how tropical diseases like chikungunya are increasingly beginning to spread in new places.

The first reported cases began to show symptoms, including acute onset of fever and muscle/joint pain, on August 5; however, due to the wide variability in incubation periods reported in the literature (2-10 days), it is difficult to pinpoint the exact source of infection. Additionally, a significant portion of individuals infected with chikungunya remain asymptomatic (estimated to be 3-28%), which further complicates efforts to identify infected cases and limit transmission.

Chikungunya is a mosquito-borne viral disease that is transmitted to humans through the bite of an infected Aedes aegypti or Aedes albopictus mosquito. The word chikungunya comes from the Kimakonde (Tanzania) word for “to become contorted,” referring to the contorted bodies of individuals experiencing the joint and muscle pains associated with the disease. In addition to severe joint and muscle pain, the most common symptoms include high fever and rash. Many patients go on to make a full recovery; however, 10% of cases experience chronic joint pain for months or even years. Elderly and immunocompromised individuals are at increased risk of more serious complications.

Italian health authorities have implemented public health measures in accordance with the Italian National Chikungunya Surveillance and Response Plan, including disinfestation and vector control measures in the Anzio and Rome areas, public communication and education efforts regarding chikungunya and how to protect against infection, and dissemination of clinical and case management guidelines for healthcare practitioners. Additionally, the WHO is recommending that those native to or traveling to the affected areas take the necessary precautions to avoid mosquito bites, such as wearing insect repellent, covering exposed skin, and ensuring windows and doors have proper screens to prevent mosquitoes from entering homes. Unfortunately, the WHO reports that the risk for further transmission remains high due to the widespread, established Aedes albopictus population around the Mediterranean basin and the high volume of tourists in the affected areas.

On September 15, the Italian Health Ministry suspended blood donations in parts of Rome and the nearby seaside town of Anzio due to the outbreak. While blood-borne transmission of chikungunya infection from transfusions has not yet been documented, investigations conducted during outbreaks in Thailand (2009) and Puerto Rico (2014) identified chikungunya virus in blood donation inventories that could potentially pose risk for blood-borne transmission.

In utero and intrapartum transmission have been documented as well, but they occur only rarely. One study detected chikungunya virus in the breast milk of infected mothers, but there have been no reports of infants acquiring the disease through breastfeeding. The US CDC encourages mothers to breastfeed even if they are infected with the chikungunya virus or live in an area with ongoing virus transmission, noting that the benefits of breastfeeding a newborn far outweigh the risk of chikungunya virus infection in breastfeeding infants.

Aedes albopictus was first detected in northern Italy in 1990. Since then, it has spread across the country—mainly along the coastal plains, but with scattered foci in almost every region. Global air travel and seaborne trade removes geographic barriers to insect disease vectors. Additionally, increased coastal temperatures have allowed the Aedes albopictus mosquitoes to colonize and adapt to the mild Italian climate. According to Dr. Roberto Bertollini, Director of the WHO’s Health and Environment Program at the time of Italy’s first chikungunya outbreak, “Climate change creates conditions that make it easier for this [Aedes albopictus] mosquito to survive and it opens the door to disease that didn’t exist here previously.”

While many other factors (eg, rainfall) drive mosquito distribution, climate change as a whole—including increased frequency and severity of weather-related and other natural disasters—could potentially result in expanded geographical ranges for mosquitoes and increased risk of vectorborne diseases in affected areas. Study of the effects of climate change on the geographical spread of vectors is still in the early stages, but some initial research suggests that increasingly mobile populations provide opportunity to transport vectors, including the albopictus mosquito, to new locations where rising temperatures may potentially result in winters that are not sufficiently cold to kill off eggs and larvae. Additionally, other models project substantial changes in the geographic distribution of mosquito vectors as a result of rising temperatures.

In light of changing environmental conditions, we are likely to increasingly see chikungunya cases turn up in new parts of the world. Surveillance systems and public health planning will have plan for these occurrences and adapt accordingly.

 

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly in near-real time to allow others to learn from these experiences in order to improve global outbreak response capabilities.

Photo courtesy of CDC/ James Gathany