In a world where climate change is of increasing concern, it is easy to separate human health and environmental health into two distinct categories. Climate change, coupled with further issues such as deforestation, urbanization, and encroachment on wildlife habitats, creates a clear connection between human and environmental health. There is a lot of scientific literature that suggests that the health of the environment strongly impacts epidemiology, which is the study of diseases. Many studies have identified that the scope and magnitude of many zoonotic diseases will only increase as the effects of warming temperatures take place. 

According to the Joint World Health Organization and Food and Agriculture Organization meeting in 1951, zoonotic diseases are “diseases and infections that are naturally transmitted between vertebrate animals and man.” However, zoonotic diseases can also be transmitted by insects, such as mosquitoes. Scientists classify 61% of all emerging infectious diseases (EIDs) as zoonotic. Currently, there are 700 million people infected and over a million deaths annually due to such diseases transmitted by mosquitoes. These diseases include malaria, dengue fever, chikungunya virus, West Nile virus, and Zika virus. As temperatures warm, it is likely that the range of many mosquito species will only increase and lead to further disease transmission. For example, Aedes spp. Mosquitoes have been shown to have thermal adaptations to the rising temperatures, including characteristics such as metabolism rates, body size, and thermal limits.

Locally, Aedes aegypti mosquitoes have recently spread to California, some of which carry dengue fever. Dengue fever is commonly spread by mosquitoes and causes symptoms such as body aches, high fever, headache, nausea, vomiting, swollen glands, and rash. This poses a risk for newly introduced zoonotic diseases to spread to new territories and infect previously unimpacted populations. The increasing prevalence of climate events such as floods and droughts may also play a role in increasing mosquito populations amid rising global temperatures. 

The danger of zoonotic diseases spreading to new territories is not limited to California. It may also impact other countries not previously exposed to zoonotic diseases, such as malaria. In Britain, a study found that by 2050, climate change will lead to an 8-14% increase in malaria transmission in Britain. The simulation also found that an increase in temperature of 1 degree Celsius would lead to an 8.3% increase in deaths caused by malaria. In the United States, malaria outbreaks occurred in 2023 after 20 years with no reported cases in the country. 

Beyond mosquito-borne zoonotic diseases, increasing interactions between humans and animals may increase the risk of disease transmission. For example, wet markets pose a significant risk of diseases changing host from animals to humans. Wet markets are markets where many animals are freshly sold. When animals are stressed in conditions detrimental to their health, it increases pathogen transmission. Further, interactions between different animal species in wet markets lead to greater pathogen spillover between hosts. 

Due to increased interactions between humans and animals due to habitat encroachment and urbanization, there are increased risks of zoonotic disease transmission. Diseases such as Ebola, SARS, and Lassa may be transmitted from animals to humans. Other practices, such as wildlife farming and wildlife hunting, contribute to increased human-animal interfaces. 

Other threats include the melting of permafrost in regions such as Russia, where viruses from prehistoric times may be exposed. Many of these viruses have unknown properties and need to be further studied to identify how they will interact with human and animal populations. Climate warming in Arctic regions is reported to be occurring at twice the rate of the global average, further expediting the thawing of unknown pathogens. Combined with issues such as water pollution, mining, and industrialization in previously undeveloped areas, permafrost thawing and its impact on zoonotic disease transmission is a significant area of further study.

As temperatures rise and the impacts of climate change take effect, it is important that these considerations are taken into account when formulating vaccines and other mitigatory measures against zoonotic diseases. Zoonotic diseases are an increasing threat and must be taken into account in parallel with human and environmental health.