Chikungunya in Brazil … and beyond?

On March 8, the Pan American Health Organization (PAHO) issued an epidemiological alert because of “an increase in the number of cases and deaths from chikungunya above the numbers reported in previous years”. The alert also noted an expansion in the areas where the disease has normally occurred since its introduction into the region. For these reasons PAHO urges “that member states intensify actions to prepare health care services … and to strengthen prevention and vector control measures”. But, of course, there are no licensed vaccines or antivirals to tackle either infection or disease. This lack of interventions is somewhat mitigated by the apparent life-long immunity conferred by infection. However, natural infection is far from the ideal route to immunity, particularly in the case of a disease where debilitating pain is a defining symptom. The intensification of the scale of disease comes at a curious milestone, as 2023 marks the 10th anniversary of the introduction of chikungunya virus into Brazil. Although, naturally, COVID-19 complicates the current picture. In an Article in this issue, William de Souza and colleagues investigate the spatiotemporal dynamics and recurrence pattern of chikungunya virus since its introduction into Brazil in 2013. Over the period studied there were more than a quarter of a million laboratory-confirmed cases (clinically diagnosed cases were far greater) across almost 60% of Brazil's municipalities. These cases mainly occurred during seven epidemic waves over the last 6 years of the study period. de Souza and colleagues find that spatial heterogeneity of the virus contributed to the recent recurrence of the disease, as areas largely unaffected by previous waves were left susceptible. That this spatial heterogeneity exists somewhat undermines the immunising effect of infection at the population level and provides insight into probable future hotspots of disease, allowing the targeting of public health interventions. However, even areas of past outbreaks cannot be overlooked, as children born since an epidemic wave affected their region will be susceptible. Spatial heterogeneity offers an explanation for observations in the PAHO alert that the virus is expanding into new areas—ie, the long-term immunological impact of infection is likely to drive the virus's spread into previously unaffected areas. Primary measures to keep chikungunya at bay are targeted at the vectors: elimination of Aedes breeding sites and—in areas of active transmission—adult mosquitoes. Personal preventive measures are also advised. But the recurrent nature of the outbreaks makes it clear that there is the need for more than these public health measures. Fortunately, a vaccine is on the horizon. A report of the phase 2 trial of the chikungunya virus vaccine, PXVX0317, shows promise and two phase 3 studies are underway or nearing completion. However, this vaccine cannot come soon enough for those facing intensifying waves of infection and disease. A crucial consideration beyond Brazil, and even the Americas, is that climate change is likely to expand the distribution of the aforementioned vectors of chikungunya virus. Making the need to directly address infection much more universal than currently thought—one such vector, Aedes albopictus, is already established in southern Europe and so has the potential to expand its range as conditions permit. As an eye opening example, Jolyon Medlock and Steve Leach stated in 2015 that “models of chikungunya virus transmission from the EU suggest that with climate change, temperatures will be sufficient in London for at least 1 month of chikungunya virus transmission by 2041–70 and across most of southeast England for 1–3 months by 2071–2100”. It is possible that these timescales have moved up now that the impacts of climate change seem to be progressing at a faster rate than anticipated just a few years ago. However, the effects of climate change are not limited to this one vector or pathogen. There is now some appreciation that, in our increasingly interconnected world, diseases should not be considered remote and hence not a concern elsewhere, particularly in high-income countries. So, as the lessons of the COVID-19 pandemic begin to fade from the public consciousness, we need to reiterate that infectious disease is a global problem that all nations should contribute to tackling. However, we should also guard against the self interest of more privileged nations ultimately hoarding vaccines and drugs when they find themselves confronted with what they thought were remote diseases. For more on PAHO's epidemiological alert see https://www.paho.org/en/documents/epidemiological-alert-increase-cases-and-deaths-chikungunya-region-americas For more on PAHO's epidemiological alert see https://www.paho.org/en/documents/epidemiological-alert-increase-cases-and-deaths-chikungunya-region-americas Spatiotemporal dynamics and recurrence of chikungunya virus in Brazil: an epidemiological studySpatial heterogeneity of CHIKV spread and population immunity might explain the recurrence pattern of chikungunya in Brazil. These results can be used to inform public health interventions to prevent future chikungunya epidemic waves in urban settings. Full-Text PDF Open AccessSafety and immunogenicity of PXVX0317, an aluminium hydroxide-adjuvanted chikungunya virus-like particle vaccine: a randomised, double-blind, parallel-group, phase 2 trialPXVX0317 was well tolerated and induced a robust and durable serum neutralising antibody immune response against CHIKV up to 2 years. A single 40 μg injection of adjuvanted PXVX0317 is being further investigated in phase 3 clinical trials ( NCT05072080 and NCT05349617 ). Full-Text PDF Effect of climate change on vector-borne disease risk in the UKDuring the early part of the 21st century, an unprecedented change in the status of vector-borne disease in Europe has occurred. Invasive mosquitoes have become widely established across Europe, with subsequent transmission and outbreaks of dengue and chikungunya virus. Malaria has re-emerged in Greece, and West Nile virus has emerged throughout parts of eastern Europe. Tick-borne diseases, such as Lyme disease, continue to increase, or, in the case of tick-borne encephalitis and Crimean-Congo haemorrhagic fever viruses, have changed their geographical distribution. Full-Text PDF