Mosquitoes and ticks are increasingly recognised as a global health risk. Recent outbreaks of mosquito-borne viruses, such as chikungunya in Guangdong, China, and West Nile virus across Europe and North America, highlight how climate change is expanding the geographical reach of disease-carrying insects. For businesses with a global workforce, the risks are clear: shifting disease behaviours present new challenges and threaten workforce wellbeing. Building resilience against these health challenges is essential.

Climate change and the spread of vector-borne diseases

Arboviruses are viruses spread by arthropods – like mosquitoes and ticks – which act as vectors, carrying the virus between hosts. Arboviral transmission rates are therefore influenced by environmental conditions. Understanding how certain insects thrive is key to predicting arbovirus distribution patterns and mitigating risks. As ectotherms, arthropods rely on external temperatures, so climate plays an influential role in their success as a species. Warmer temperatures can accelerate viral replication. With life cycles closely aligned to seasons and climates, both the seasonal and long-term trends of arboviruses can be predicted.

In the short term, warmer and milder winters allow insects to remain active for longer. Seasonal cold spells are required to suppress vector populations ahead of the following year. Freezing temperatures typically reduce vector populations by killing eggs and larvae or forcing adults into dormancy. Without these dips in temperature, vectors can potentially sustain breeding year-round, which in turn increases the likelihood of transmission.

It is relatively straightforward to anticipate an increase in dengue following a monsoon season, for example, but the real art lies in knowing how bad it will be each year

In the medium term, global climate patterns such as the El Niño-Southern Oscillation (ENSO) can play a key role in influencing vector success. During warmer ENSO phases, when conditions are favourable, vectors may spread further than usual, though effects vary by region. ENSO events can also cause unusual rainfall patterns, creating temporary breeding grounds in typically dry areas. If mild winters persist for several years, there may be no natural pause in disease transmission. Even with reduced breeding, sustained populations during colder months can lead to large outbreaks when summer returns. While some years may provide favourable conditions leading to surging outbreaks, the following year could bring a cold snap that brings vector populations back under control again.

In the long term, climate change is making previously inhospitable areas suitable for disease-carrying insects. Higher altitudes and latitudes may initially only support these species during summer or favourable ENSO cycles. Over time, and with other contributing factors, what was once an uncommon outbreak gradually could become the new normal, leading to geographic expansion for vectors. Though this process is slow and can take decades to actualise, geographic expansion can pose a public health risk to vulnerable populations by introducing arboviruses where there is little prior exposure, immunity, or preparedness.

Conditions that help disease-carrying vectors thrive 

While warming temperatures make cooler regions more hospitable to mosquitoes and ticks, they also make already-hot areas drier, contributing to desertification and the spread of arid zones. Yet arthropods have adapted remarkably well to these changing conditions. Understanding the environmental and biological factors that support their life cycles is key to managing the risks they pose. Mosquitoes are highly adaptable and capable of exploiting human behaviours and infrastructure to survive.

A recent reemergence in local transmission of malaria in the US demonstrates that the required ingredients to sustain malaria transmission are present

Environments that become drier as a result of increasing temperatures would typically cause insect populations to perish. In drought-affected settlements, water is stored for human use and consumption. Rain collection systems, open containers, rooftop cisterns, and underground tanks can all become breeding sites. If the water is stored improperly, insects can access it and have the perfect habitat to thrive. This perfect cocktail of heat and moisture turns an unviable habitat into a mosquito breeding oasis.

Even in urban environments where water storage is managed properly, standing water is a significant issue. Infrastructural development creates even more opportunity for mosquitoes to thrive. Drainage infrastructure often cannot keep up with rapid urbanisation. Combined with deforestation, this can also increase flooding risks. Hard road surfaces and buildings offer plenty of places for water to pool and, even if it is well planned, it is impossible to ensure perfect water run-off everywhere in a city. Mosquito larvae can survive in even the smallest reservoir of water, even something as small as a bottle cap. 

The combination of natural and man-made pools provides endless viable breeding sites, making it nearly impossible to eliminate them all, even in the hottest of locations.

Why data tracking matters for risk managers

Disease trends often occur in predictable, seasonal cycles. It is relatively straightforward to anticipate an increase in dengue following a monsoon season, for example, but the real art lies in knowing how bad it will be each year. Looking beyond the annual seasons, longer-term trends can also be predicted, and using this long-term modelling it is also possible to start to predict how bad a year might be. Harnessing data analysis and trend insights enables response preparation. For example, additional healthcare staff can be trained, healthcare infrastructural developments can be planned, water management systems can be introduced – all ahead of a predicted outbreak. 

Vector-borne disease outbreaks are not isolated to developing nations; they can emerge anywhere the right conditions are present. A recent reemergence in local transmission of malaria in the US demonstrates that the required ingredients to sustain malaria transmission are present. Malaria cases unrelated to overseas travel remain incredibly rare in the US. However, these events offer forecasting insights and should be analysed so that plans can be developed in advance. Similarly, dengue, which is typically associated with the tropics and subtropics, has seen a notable increase in case numbers in Europe in recent years. This is a trend that should be closely monitored to ensure that nations are properly prepared.

Seasonal endemic diseases should also be monitored, as a minor imbalance can lead to epidemic proportions. In countries where seasonal outbreaks are anticipated, the health services are typically braced for an increase in cases. However, where surges are beyond projected levels, services can become overwhelmed. Furthermore, seasonal outbreaks have the potential to result in prolonged disease surges or year-round outbreaks. With rising patient numbers, healthcare infrastructure may face increased strain.

Plan business trips outside of vector-borne disease seasons and offer post-travel health checks for those returning from higher-risk areas

While diseases are emerging in some new locations, many of these diseases are not unfamiliar. Effective monitoring of these trends puts businesses in the best position to implement mitigation measures proactively, before problems arise. When properly managed, many vector-borne diseases can be effectively mitigated.

Practical tips for businesses and what risk managers should know

• Insect bite prevention measures are the first line of defence against vector-borne diseases
• Consult with a doctor prior to travel; some vector-borne diseases can be vaccinated against, while the risk of malaria can be reduced by taking malaria prophylaxis tablets. However, even when these measures have been taken, the most important strategy for all travellers is insect bite avoidance
• Ensure staff are suitably educated and equipped to eliminate mosquito breeding sites. Taking simple measures, such as sealing water tanks, reduces access to breeding sites and makes water storage more hygienic
• Plan business trips outside of vector-borne disease seasons and offer post-travel health checks for those returning from higher-risk areas
• Consider corporate responsibility in joining the community effort to eliminate potential breeding sites by clearing standing water and securing water storage systems. Encourage the use of air conditioning during vector seasons and assess the possibility of installing mosquito nets on the windows
• Where offices are situated in locations more prone to seasonal surges, consider if company-funded clinics and healthcare access would help support the workforce. It is important that staff deployed abroad can continue to reliably access health services when local services could be prone to being overwhelmed.

Conclusion

As businesses are becoming more aware of the impacts of climate change on operations, it’s important to look at the full spectrum of climate-associated risks. Though the primary impacts of climate change, such as flooding, are important, the secondary consequences, such as outbreak risks and strain on healthcare infrastructure, are sometimes overlooked. 

In vulnerable locations, outbreak preparedness should sit alongside other disaster business continuity plans such as earthquake procedures or fire drills. Accurate monitoring, quality data analysis, and proactive preparation are important first steps in protecting operations. If a particularly hot and wet season is forecast, increase communications to educate staff, ensure there is access to any relevant vaccinations, and work with local authorities to ensure safe communities for everyone. Vector-borne diseases may be difficult to eliminate entirely, but, with the right measures in place, their impact can be significantly reduced.