Environmental temperature change of climate and rainfall distribution and intensity, the migration of wild animals, and movement of domestic animals and the migration of people and increasing tourism are all affecting the distribution and abundance of insect, arachnid and molluscan vectors of disease. Thesustained control of the insect vectors of dengue and leishmaniasis is difficult because their high reproductive potential allows the vector populations to recover quickly after intervention given adequate breeding conditions. By contrast, tsetse flies, the vectors of trypanosomiasis, have a lower reproductive potential and could be eliminated over large areas, given adequate organization and surveillance. There are several developments which should be implemented. A number of actions and policy changes are proposed. These include: improved advice to local farmers, and the use of more appropriate vaccines and other medicines, the prevention of the sale of OTC antibiotics, greater knowledge of the ecology of vectors, the GM/gene editing of mosquitoesand the use of remote sensing devices.
Glossary: : Zoonotic disease; Pertaining to a zoonosis: a disease that normally exists in animals that can be transmitted to and infect people, or that can be transferred from people to animals and infect them.
The earth’s temperature has risen about 0.8o C since 1880. It has been estimated that 20-30% of all vertebrate animals would become extinct if the average temperature rises by the 2-3 ° C anticipated this century1.
The distribution and intensity of rainfall is also changing, leading, for example, to increased frequency of droughts and floods in India2. The effect is that the incidence, especially of vector-borne animal disease is likely to rise. Climate change is resulting in emergence and re-emergence of a plethora of infectious, mostly zoonotic, diseases throughout the world. Around 75% of the emerging animal diseases are zoonotic in nature 1,2,3(Table 1) with wildlife being one of the major sources of infection4.
The livestock sector is extremely important to rural livelihoods and the global economy. In 2013, there were an estimated 38 billion livestock in the world, or nearly five animals for every person. Most (>80%) were in developing countries and around one billion poor farmers keep livestock1.
The burden of animal disease in developing countries is high: disease probably kills 20% of ruminants and more than 50% of poultry each year, causing a loss of approximately US$ 300 billion. Climate change can exacerbate these losses as, of 65 animal diseases identified as most important to poor people, over half are climate sensitive1.
Vectors: arthropods (insects and arachnids), rodents, Molluscan and domestic and wild animals are all capable of being vectors of disease and are especially sensitive to climate change. Changes in rainfall and temperature regimes may affect both the distribution and the abundance of disease vectors, as can changes in the frequency of extreme events. Infectious diseases are transmitted by arthropods and rodents and also are disseminated by water, food, and air. Arthropod vectors tend to be more active at higher temperatures, when they need to feed more regularly to sustain the increase in their metabolic rate. This enhances the chances of infections being transmitted between hosts so that small changes in vector characteristics can produce substantial changes in disease1. For example, there is increased research activity in searching for better control of the three diseases caused by the trypanosomatids, the related kinetoplastid pathogens: Leishmania major, Trypanosoma brucei and Trypanosoma cruzi . These protozoa cause some of the most debilitating diseases of humans: cutaneous leishmaniasis, African Sleeping Sickness, and Chagas disease.
These diseases possess complex life cycles that involve development in mammalian and insect hosts5,6although they have dissimilar geographical distributions. This reflects their different insect vector characteristics and range of vector contact with humans. These diseases disproportionately afflict poor and remote populations with limited access to health services. Moreover, their pathogenic mechanisms are poorly understood, but typically entail immunological processes, so that herd immunization reduces the number of susceptible animals in a population and augments herd immunity making infection more difficult to spread4. Increased environmental temperature both increases the rate of development of the leishmania parasite and the activity the sandfly vector. The vector takes more frequent blood meals, which in turn enhances transmission (Table 2)7. Higher temperatures also increase the developmental rate of ticks and their over-winter survival rate is improved. This will increase the risk of, for example, Lyme Disease spread8(Table 2).