The damage that invasive species can cause to the environment and the economy are well known, but impacts on human health have been much less analysed. However, invasive species can cause impacts ranging from psychological effects, phobias, discomfort and nuisance to allergies, poisoning, bites, disease and even death. Invasives experts Giuseppe Mazza and Elena Tricarico of the University of Florence, Italy say that in addition to these direct effects, some work in more indirect ways. Humans are menaced by alien invasive species affecting the services provided by ecosystems. “These services are vital to our well-being: changes may decrease the availability of drinking water and of products from fisheries, agriculture and forestry, alter pollination and impoverish culture and recreation,” say Mazza and Tricarico.
An example of these secondary impacts is the spread of the water hyacinth, Eichhornia crassipes, which causes algal blooms, oxygen depletion and fish kills. It can also provide a suitable habitat for mosquitoes and snail species such as Biomphalaria sudanica and B. choanomphala, vectors for the water-borne parasite Schistosoma mansoni, encouraging the spread of malaria and schistosomiasis (snail fever or bilharzia).
At least 42 species of introduced birds threaten human health. Most are parrots, pigeons and doves and waterfowl, introduced as pets and now common in urban areas. They can pass on psittacosis, which can cause flu-like illness to severe pneumonia, cryptococcosis, which can cause meningitis, and Listeria, which can cause fever and diarrhoea. All of these diseases can result in death, albeit rarely. Introduced game species can also carry Salmonella and other causes of human gastrointestinal problems. Invasive birds can also impact health through bird strikes at airports and through noise pollution. However, there are very few studies focused on the invasive species element of disease outbreaks and arguably more should be done to monitor the disease status of traded birds and the impact of alien birds in urban areas.
Invasive freshwater species also pose serious risks. Invasive catfish have poisonous spines that can cause disease in anglers, leading to foreign bodies, respiratory issues, arterial hypotension and irregular heartbeat. An outbreak of the disease tularemia, which can cause fever, fatigue and death if untreated, was linked to fishing for the invasive red swamp crayfish, Procambarus clarkii. The redclaw crayfish Cherax quadricarinatus is a potential disease vector for lethal microbes such as Vibrio cholerae and Escherichia coli, more commonly known as E-coli after recent outbreaks.
Climate change is likely to impact the distribution of alien species relevant to human health. It is expected that it would increase the risk of vectors of West Nile Virus and Crimean-Congo haemorrhagic fever virus entering Europe. The Asian tiger mosquito, Aedes albopictus, associated with West Nile virus, dengue virus and chikungunya, is likely to become more established in many temperate areas, including urban centres around London and the Southern UK. Phlebotomus sandflies, which carry leishmaniasis, a potentially fatal disease, are expected to increase their distribution northwards. Common ragweed, Ambrosia artemisiifolia, which has allergenic pollen, is likely to spread further in the UK and southern Scandinavia because of warmer summers and later frosts, and have greater effects, because of more pollen production through higher photosynthesis and extended growing seasons.
We need more information on how invasive species spread and the way diseases take effect so we can plan strategies to minimise their effects. The role of human activity in allowing the spread of invasive species, and how this may change with climate change is a critical area for investigation. Multidisciplinary efforts, such as One Health, which examine linkages between human and animal activities and their environments, will be crucial in getting to grips with invasive impacts on health. Mazza and Tricarico argue “A better understanding of drivers and management options of alien diseases and vectors as well as joint efforts in educating the public and decision-makers is crucial since most health consequences of global change, biological invasions included, affect the weakest sectors of society, i.e. developing countries and children.”
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