Climate is the pattern of atmospheric conditions over a long period of time. Also can be described as the atmospheric conditions that prevail in a given region over a period of time. This includes not only the average weather but also values of climatic conditions that prevail at extreme ranges, their variability, and the frequency of various occurrences. These climatic elements include solar radiations, temperature, humidity, precipitation, atmospheric pressure and wind in terms of speed and directions. Therefore climate change is the variation of global and regional climates over time. These changes can be caused by processes internal to the earth, external forces or human activities.
Vector is an agent that delivers a pathogen or other biological materials from one place to the other. It’s a vehicle that only helps in transportation of infectious materials. Vectors do not cause the disease but act a significant role in the transmission of a disease. Although vectors can transmit pathogens to both animals and plants, our main focus will be those that transmit to animals.
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Vectors can be categorized into two classes:
• Mechanical vectors
This is a type of vectors that act as transport vehicle only, whereby the infectious agent does not depend on the vector in any part of its cycle. In fact, most of these agents can be transported by any vector without making any major difference.
• Obligate hosts
This is a class of vectors that plays an important role in the pathogens life cycle. The insect is needed by the pathogen to complete some of its developmental stages before it is transmitted to its final host eg mosquito from a genus Anopheles is specifically required by Plasmodium malariae to complete parts of its development.
Most vectors are bloodsucking insects such that the transportation of the pathogen may be through a direct route.
Infectious diseases are illnesses that result from a disease-causing organism getting into a hosts body and the organism causes reactions toward the host tissues either due to the presence of the agent or the toxins they produce. They can also be called transmissible diseases. Infectious diseases can be caused by either bacteria, virus, fungi or parasites. Oftenly infectious diseases are through contact with infected people, animals, vectors, parasites or ingestion of contaminated food.
The ecology of vector-borne diseases is one of the complex scenarios to address since climate is always a major factor to be considered due to its influence in disease transmission cycles and disease occurrences. Vectors involved in vector borne diseases are very sensitive towards climatic changes and surrounding environmental factors. This could be due to; vectors and hosts survival, reproduction, development and distribution; pathogen development, replication, and transmission; geographical range of pathogens, vectors, and hosts; human behavior; disease outbreak frequency, onset, and distribution.
The complexity of these interactions is an indication that the effects of climatic changes and the nature and extent of non-climatic factors vary by disease and by location. A disease with well-known transmission cycles can be affected very differently by climate change.
So far, we cannot deny that in the last 150 years, the climate has changed. The levels of carbon dioxide and methane gases in the atmosphere has increased at an alarming rate. The earth's temperature has risen and if no efforts are done to reduce the amount of greenhouse gases in the atmosphere, global temperature is expected to rise more rapidly by the end of the 21st century. This will make it hard for animals and plants to adapt toward the heat changes. Sea levels have risen with up to 8 inches, ocean acidification has increased by 30% and we can't fail to admit that in the last 2 millenniums, we have experienced intense rainfall, flooding, typhoons and in some areas extreme lack of rain. All these changes pose a risk toward infectious diseases.
Environmental temperature is one of the factors that affect life and transmission of diseases. Temperature has an effect on the distribution of vectors. As the temperature continues to rise, insects in low latitudes may find new habitats in mid and high latitudes. Some vectors of Malaria, African triponomiasis, plague, and dengue have distributed to wider ranges mostly into areas of high latitudes. Also, the temperature has been observed to have the potential to restrict disease distribution. A good example is Aedes aegyptia, a mosquito vector for yellow fever and dengue fever. The experiment shows that larvae of these species perish when the temperature passes 34 degrees and adult could not survive temperature above 40 degrees. As global warming increases, vectors such as A. aegypti may get extinct. Low temperatures also provide optimum conditions for the spread of infections such as Influenza. Also, long hours of sunshine has been observed to act synergetically with temperature during Cholera periods to create favorable conditions for the multiplication of Vibrio Cholerae in the aquatic environment.
Humidity is another factor with a great impact on pathogens. Pathogens of airborne infectious disease such as Influenza tend to be responsive in humid conditions. Their survival rates of water-borne infections near water surfaces are getting narrower due to the drying of surface water. A number of hosts have shown a tendency to respond to humidity positively. Humidity of lower than 60% shortens the lifespan of mosquitos that cause malaria while those that cause West Nile fever and dengue fever migrate toward non-traditional regions when high temperatures are coupled with dry spells.
Many vectors have been found to be positively affected by rainfall. Larval development of mosquitoes is usually accelerated by rainfall while their adults breeding sites could be limited by drought. Also, excessive rainfall may have a catastrophic impact on the mosquito population by sweeping away their breeding grounds. Drying of river beds allows accumulation of organic matter that provide Culex a vector for West Nile fever breeding grounds. During rainy seasons, number of Chorela cases are usually high and this is associated with the increase in fecal materials stirred up by rain.
Wind is also a key factor in the spreading of airborne diseases. Bacteria, fungi, and viruses are easily transported across dust particles reaching hosts easily According to Chen et al.,2010, the presence of desert dust during Asia Dust Storms (ADSs) are associated with increased concentration of cultivatable bacteria, fungi, and fungal spores. Also, Influenza during ADSs was higher than normal days. Wind also has a dual effect on vectors affecting vectors for malaria both negatively and positively. Strong winds reduce bitting mosquitos and also extend their flight distances.
Climate change may have contrasting effects on both pathogens and vectors thus disease outcomes may be different but what we are sure is outcomes that favor the survival of vectors and spread of infectious diseases no matter how small they are, may be catastrophic. This continues to pose a health risk to a human in relation to infectious diseases. Efforts toward reducing vulnerability should be adopted at either scientific or social level because the rate at which climate change is taking place demands an urgent action globally.
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