Warming planet, rising risks: Escalating threats of arboviruses in Europe (Valneva symposium)

Author(s):  Comité scientifique de Travel Health Xpert

Japanese encephalitis (JE) is a risk in 24 countries, mostly in Asia. Each year there are about 100,000 cases and 25,000 deaths globally [1]. “Travelers are relatively unlikely to come in contact with the virus and fewer than 1% become infected. But for those who get it, it can be devastating,” Dr. McGuiness explained. There is no specific treatment, only a vaccination. The disease can lead to permanent neurologic long-lasting damage.

The JE virus can only be transmitted by mosquitoes, and humans are a dead-end host. It’s naturally transmitted in a cycle between mosquitoes and waterbirds, while pigs serve as amplifying hosts [2]. Case reports of human-to-human transmissions exist via blood transfusions and organ transplantations. Prior to 2022, only sporadic reports of locally acquired human JE virus infections had been reported in Australia.

A new virus genotype (IV JEV) led to an outbreak in South-Eastern Australia from 2021 to 2022. The outbreak may have been caused by an increase of waterbirds due to heavy rainfall and the close proximity of Australian inhabitants to piggeries. All in all, 46 human cases have been reported, most of them being older adults [3].

As most JE cases are asymptomatic, diagnosis can be challenging. PCR is the most specific test. “Where the disease is endemic, it is more of a childhood disease, and adults are typically immune. However, since 1973, over 90% of published cases have been in adults, and in Australia, primarily in older adults,” Dr. McGuinness noted. The only way to prevent JE is by avoiding mosquito bites or getting vaccinated.

Chikungunya now present in more than 100 countries

“Previously, chikungunya was a disease encountered in Africa and Asia. But since 2014, it has spread to more than 100 countries,” Dr. Norman said. Endemic areas are expanding and vectors are Aedes aegypti and Aedes albopictus.

The acute stage of the disease lasts less than three weeks, with predominant symptoms including fever (in 85% of patients) and neurological or ocular symptoms such as conjunctivitis [4,5]. Risk factors for complications include older age (>65 years), comorbidities, and pregnancy [4]. The post-acute stage lasts three weeks to less than three months, during which arthralgias are frequently observed [4–6]. Some patients suffer from a chronic stage (lasting more than three months), most frequently experiencing chronic arthralgia [5,6]. Risk factors for developing a chronic stage include age >40 years, severe acute disease, and underlying osteoarthritis.

Rash and fever can be symptoms of chikungunya during the acute stage, but they are also seen with measles, rickettsial diseases, or Zika infection. Therefore, diagnosing chikungunya clinically can be difficult. Importantly, not only infectious disease specialists but also general practitioners hould be aware of chikungunya and be able to identify its risk factors [7].

In the acute phase, a PCR test for chikungunya virus RNA is recommended within the first five days [7]. Serologic testing can be performed at least seven days after symptom onset. In the chronic phase, chikungunya virus antibodies can be detected; otherwise it is only possible to exclude other causes of arthritis [7].

“The vast majority of cases are transmitted by vectors (mosquitos),” Dr. Norman highlighted. Mother-to-child transmissions can happen in outbreaks with a frequency of 15% (but up to 50% if intrapartum viremia exists) [8]. Moreover, transmissions are possibly by blood transfusions. A prevalence of up to 2% of chikungunya RNA has been found in asymptomatic donors [9].

Recently, the Committee for Medicinal Products for Human Use (CHMP) of the EMA adopted a positive opinion recommending the authorization of the first single-dose chikungunya vaccine. This development offers hope that the risk of the disease can soon be diminished.

Climate change fuels arbovirus infections

Different arbovirus transmission cycles exist: an enzootic cycle involves direct spillover from wildlife to mosquitoes and humans, an epizootic cycle amplifies viruses in domesticated animals, infecting humans via mosquitoes, and an urban epidemic cycle involves direct transmission between humans and the vector.

Dr. Huits emphasized the increasing suitability of the climate in Europe, expanding potential vector habitats. “By 2030, 2040, and 2050, the range of vectors could extend up to southern Sweden, due to global warming trends.”

Temperature significantly influences insect life. It boosts host-seeking behavior and blood meal intake, as well as pathogen development and transmission [10]. “This is directly related to vector abundance and affects the mosquito-to-human ratio, with a higher chance of getting bitten,” Dr Huits stated.

Travelling facilitates the movement of humans and vectors, thus also causing the establishment of novel pathogen transmission cycles. Therefore, it is imperative to adopt a one-health approach, focusing not only on human health but also on mosquito ecology and the influence of animal health.

All speakers agreed that arboviruses are an emerging public health concern. Physicians must be aware of formerly “tropic infections” and be able to diagnose them.

1. Quan TM, et al. eLife 2020;9:e51027
2. McGuinness SL, et al. Curr Infect Dis Rep 2023:25:111-22.
3. McGuinness SL, et al. J Travel Med 2023:30:taad029.
4. Vairo F, et al. Infect Dis Clin North Am 2019;33:1003-25.
5. Bartholomeeusen K, et al. Nat Rev Dis Primers 2023;9:17.
6. Amaral JK, et al. Viruses 2019:11:289.
7. Simon F, et al. Med Mal Infect 2015;45:243-63.
8. Contopoulos-Ioannidis D, et al. PLoS Negl Trop Dis 2018;12:e0006510.
9. Gimenez-Richarte A, et al. Blood Transfus 2022;20:267-80.
10. Reinhold JM, et al. Insects 2018;9:158.

Valneva Lunch Symposium

Warming planet, rising risks: Escalating threats of arboviruses in Europe

Dr. Sarah McGuiness - Department of Infectious Diseases, Alfred Hospital, Australia

Dr. Francesca Norman - National referral Unit for Tropical Diseases, Ramon y Caja Hospital, Spain

Dr. Ralph Huits - Department of Infectious Tropical Diseases and Microbiology IRCCS Sacro Cuore Don Calabria Hospital Negrar, Italy

NECTM9 (9e Conférence d'Europe du Nord sur la médecine des voyages), Copenhague, Danemark, 22-24 mai 2024.

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