Climate change modulates the disease occurrence

Apart from economic impacts, there is great danger that climate change may alter disease burden in animals and plants that will have significant impact on the survival of species.
Climate change modulates the disease occurrence

Climate change is a global reality whose impacts are felt by both developing and developed countries. According to UN Convention on Climate, "Change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods". It has been estimated that average global average economy is predicted to be down by 23% by the end of this century, and there is general consensus among various stake holders that climate change will be major contributor for such alteration. There has been also campaign by 'Climate Skeptics' (people who are in denial mode) to accept the occurrence of climate change and its impacts, nevertheless, their argument has no strong base as we have solid scientific evidence from last 100 years in favour of altered climate conditions. The bottom line is clear: Global climate change is a real phenomenon, and its impacts are also real. That is why former US Vice President, Mr. Al Gore said that people need to stop financing denial of climate change. 

Apart from economic impacts, there is great danger that climate change may alter disease burden in animals and plants that will have significant impact on the survival of species. In last two decades, researchers have studied various aspects of 'Climate Change vs Disease' relationship, and most empirical studies have shown complex yet convincing results confirming the long-term effects on animals and plants. There are numerous examples of potential climate change side effects on the disease occurrence. In a recent study published by the Zoological Society of London, researchers have found that higher temperatures and precipitation levels mean greater harm by parasites to developing chicks (Great kiskadee chick). In another potential climate change side effect example, it have has been observed that Lemur parasites may not only expand across Madagascar but also to other areas. 

 The most apparent effect of Climate Change will be the extension of the geographical range of pathogens. It has been predicted that many global diseases will be shifted to other regions which previously had no occurrence of these diseases. For example, according to UNEP/GRID (2005), distribution of the primary Malaria agent will be possibly extended toward north and south regions of world. Therefore there are more chances of extended malaria across the globe due to climate change. Tick borne viral diseases are also said to be impacted by the climatic alterations. It has been reported that erratic climate warming may effect vertical distribution of Tick-borne Encephalitis in Central Europe. The increased level of temperature has been shown to have cascading effect on the host-parasite system due to climate change, which can lead to the unusual spread of various diseases. In generally, increased temperature may effect disease causing organisms in many ways including, rapid growth and multiplication of pathogen, early and prolonged transmission and possibility of year-round transmission. It is interesting to note that rising temperature can benefit pathogen in many ways. For example, it has been observed that species of parasitic worms is using the rising temperatures to increase its chances of survival at the cost of the fish populations it uses as hosts. 

Shifting parasite distributions and diseases could have ripple effects on people too. The disease burden in human population will show incremental increase in both developed and developing countries. Also there are more chances of enhanced infection in low economic/poor countries located in Asia and Africa. It will also increase the burden on the national economies of different countries as more funds need to be allocated for the disease management. 

The global warming and climate change is also a major trigger for the onset of many emerging and re-emerging diseases. Recent surge in emerging infectious diseases (EIDs) has brought new challenge for both developed as well as developing countries. In a short duration of 6 years, world has suffered from three major deadly emerging diseases. World is facing a new emerging viruses occurring approximately after one year originating from animal hosts. 

   There is another concern which is being presently felt by ecologists that how climate change modulates the 'Biodiversity vs disease' relationship. Any negative effects of climate change on biodiversity may affect disease transmission, because biodiversity may act as a buffer against disease propagation. Biodiversity plays a dual role in the propagation of disease: It can either become safe haven for novel pathogens or reduce the disease risk. Two theories have been elaborated to explain the relationship between biodiversity and disease. Whilst 'Amplification Effect' theory is in favour of direct relationship between disease and biodiversity, 'Dilution Effect" theory stresses on inverse relationship. It is early to say which theory is more acceptable under the influence of climate change as more investigations are needed to reach to any final conclusion. 

    In conclusion, it is evident that there is link between climate change and outbreak of diseases in both humans and other organisms.  However, all disease outcomes should not be casually linked to climate change. Pole-ward direction or spread of disease from one region to another could have severe consequences on the whole ecosystem. There is threat of 'New Emerging Diseases' spreading to new areas and this may badly affect the global health. 

  It is pertinent to understand that health managers need to implement disease eradication campaign cautiously because there is always danger that climate effects may hinder such campaigns. For example, initiating a campaign to eradicate a disease in a tropical region without knowing that it has already shifted to other areas will render control efforts ineffective. It seems only right that before embarking on eradication programmes, public health authorities must consult epidemiologists and ecologists, seeking a broad scientific consensus. But first, we need innovative research and systematic monitoring programmes to obtain first-hand information about patterns of disease occurrence.

Dr. Ummer Rashid Zargar is SERB-DST Fellow, Department of Zoology, CUK, Sonwar Campus.

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