Summary of this major publication : Chikungunya is gaining ground – What makes Chikungunya special? – Lifelong protection
Encouraging message for Chikungunya vaccine candidates
A study by scientists at the Institut Pasteur in Cambodia (IPC) encourages the further development of a vaccine against the Chikungunya virus. In a recent publication, they provided evidence for a long‑lasting immunity against several different strains of the virus.
Chikungunya is gaining ground
The Chikungunya virus emerged from the Africa and spread to Asia in the 1960s. It is transmitted by Aedes aegytpi, a mosquito that lives in the tropics. This caused Chikungunya outbreaks in the 20th century to be limited to countries and territories with a tropical climate. But in 2005, a new strain of Chikungunya virus again spread eastward across the Indian Ocean islands and struck the French overseas department of La Reunion island, infecting nearly one third of the population before finally re-emerging in Southeast Asia. This mutated strain could be more easily transmitted by Asian tiger mosquitoes (Aedes albopictus). This particular mosquito species survives in colder climate and was already endemic in Mediterranean Europe. Consequently, European travelers infected by the Chikungunya virus in Asia introduced the virus several times to France and Italy.
What makes Chikungunya special?
Chikungunya shares a lot of common features with other tropical diseases like dengue fever and Zika. All are spread by the same group of mosquitoes and induce similar symptoms like fever, muscle and joint pains and rash. This makes it often difficult to clinically differentiate the diseases caused by each of the three viruses, especially as they now circulate together in many tropical countries. Chikungunya infections are unique in that they can cause severe joint pain that can persist in patients for years. Also unusual is the frequency and pattern of Chikungunya outbreaks as they are unpredictable, followed by the disappearance of the virus for years or even decades. Despite many efforts there is neither a specific treatment nor a vaccine for Chikungunya available at this time.
Chikungunya circulated in Asia since the 1950s and was reported in Cambodia in the 1960s-70s. Due to the tragic historical events in Cambodia in the 1970s – early 1980s there was no record of the disease afterwards, even though scientists looked for it as early as the 1990s. In 2011, the virus appeared in Cambodia again. An outbreak in a rural village east of the capital Phnom Penh was investigated thoroughly and found Chikungunya infections in nearly half of the villagers, but unevenly across age groups: elderly villagers born in the 1930s-70s were less affected by the outbreak. This raised the question whether these people were infected with Chikungunya decades ago and therefore remained protected during the recent outbreak. Four years after the outbreak IPC researchers returned to the village to investigate the immune response across different age groups. As the viruses circulating in the 1960s-70s in Asia were significant different from the virus that caused the recent epidemic in the region, the study tested the villagers’ immune response against several ancient and current Chikungunya viruses. Older people showed a stronger immune response to the ancient Asian virus than the younger villagers. This indicates that the protection against the Chikungunya virus persists for decades as the older Cambodian villagers remained immune approximately forty years after their infection. The IPC scientists also reported a broad immune response against several Chikungunya strains no matter which virus strain – ancient or recent – infected the villagers. Taken together, this supports the importance of the development of a Chikungunya vaccine. There is no lack of vaccine candidates but it is difficult to perform the final testing of promising vaccines as this is normally done in regions with a high risk of infection. A successfully introduced and efficacious vaccine would show a decrease in infection. Chikungunya is widespread across the tropics and subtropics but outbreaks appear unpredictable. It is therefore is very difficult to choose a suitable area for such vaccine trials. Improved knowledge of the natural course of infections, such as provided by the recent IPC study, should encourage the efforts towards a licensed vaccine as the resulting immunity could remain lifelong.
Broad and long-lasting immune protection against various Chikungunya genotypes demonstrated by participants in a crosssectional study in a Cambodian rural community, Emerging Microbes & Infections (2018), 7:13
Heidi Auerswald1, Camille Boussioux1, Saraden In1, Sokthearom Mao1, Sivuth Ong1, Rekol Huy2, Rithea Leang2, Malen Chan3, Veasna Duong1, Sowath Ly3, Arnaud Tarantola3,4 and Philippe Dussart1
1 Virology Unit, Institut Pasteur du Cambodge, Institut Pasteur International Network, PO Box 983, Phnom Penh, Cambodia
2 National Center for Parasitology, Entomology, and Malaria Control, Phnom Penh, Cambodia.
3 Epidemiology and Public Health Unit, Institut Pasteur du Cambodge, Institut Pasteur International Network, PO Box 983, Phnom Penh, Cambodia.
4 Unité d’Epidémiologie, Institut Pasteur de Nouvelle-Calédonie, Institut Pasteur International Network, Noumea, New Caledonia