The “big five” infectious diseases (malaria, dengue, yellow fever, chikungunya, Zika) and their response to climate change is of huge global concern. Climate change can affect different actors along the infectious disease chain including pathogens, vectors and hosts. In order to control efficiently potential outbreaks we need accurate predictions, which represents a major challenge in risk management planning.
Climate change: a drought scenario
The consequences of climate change can lead to different scenarios in different habitats. In rural areas, lack of rain leads to drying out of ponds and stagnant water, which compromises the habitats for breeding mosquitoes. Mosquitoes are a common vector for infectious disease transmission and therefore less rain means less stagnant water, less mosquitoes and less host infections.
In contrast, in urban areas drought leads to less effective flushing of mosquito eggs and immature mosquitoes from drains and sewers, causing higher mosquito populations in cities and increasing host infection risk.
What influences the risk of infectious diseases?
The vector-borne disease risk partly depends on climate factors. Increasing temperatures, changes to geographic patterns of rainfall, increasing climate variability, increasing frequency and severity of extreme weather events will drive the disease profiles. Moreover, dynamics of pathogens, vectors and hosts will change in response to climate change and will affect fitness of pathogens and vectors. There is a high risk of tropical/subtropical vector-borne diseases spreading into temperate zones.
There are also climate-independent factors affecting infectious diseases, which influence disease incidence and must not be neglected. Socio-economic factors determine how frequently people are bitten by vectors (such as how residences are constructed and air conditioned). Efforts to control vector-borne diseases to prevent, diagnose and treat infections are clearly influencing the disease profile. Also, vectors and vector-borne pathogens are being dispersed internationally with increased travel and human migration.
In order to control the spreading and outbreaks of infectious diseases it is crucial to predict climate change and behavior of pathogens, their vectors and hosts. Mathematical models need to consider the effects of climate-dependent and climate-independent factors to get the most accurate predictions. This is essential for the development of policies on management of vector-borne disease risks, the design of public health programmes and the identification of research gaps.
For more details on this topic you can read the original Minireview, ‘Climate change and vector-borne diseases of public health significance’ by Nicholas H. Ogden in FEMS Microbiology Letters.