They will be widespread and unpredictable.
By
Dr. Nitish
Priyadarshi
An outbreak of the Ebola virus has killed
14 people in western Uganda
last month. There is no treatment and no vaccine against Ebola, which is
transmitted by close personal contact and, depending on the strain, kills up to
90 per cent of those who contract the virus. In recent years, Uganda has been
hit with three Ebola outbreaks, the worst of which was in 2000, when more than
half of the 425 people infected died.
Cases of Japanese Encephalitis (JE) has gone up to
50 in the Assam State
in Eastern India . The areas mostly affected by
Japanese Encephalitis are Kamrup, Sivasagar, Dhubri, Morigaon, Darrang and
Nalbari. More than 400 people in northern India have died last year from
encephalitis, a rare condition that causes inflammation of the brain. Around
347 people have died in Uttar Pradesh, while 54 children have died in the
neighbouring state of Bihar . Cases of malaria
is increasing every year in the state of Jharkhand ,
Assam
With over 2,50,000 people testing positive for malaria last
year, Orissa topped the chart for reporting the highest number of malaria
cases. This was followed by 95,000 cases reported from Chhattisgarh and over
61,000 registered in Madhya Pradesh.
A 1996 report from the London School of Hygiene and Tropical
Medicine calculated that, of ten of the world’s most dangerous vector-borne
diseases (malaria, schistomiasis, dengue fever, lymphatic filariasis, sleeping
sickness, guinea worm, leishmaniasis, river blindness, chagas’ disease and
yellow fever), all but one were likely to increase, or in some way change their
range as a result of climate change.
In recent years, vector-borne diseases (VBD) have emerged as
a serious public health problem in countries of the South-East Asia Region,
including India .
Many of these, particularly dengue fever, Japanese Encephalitis (JE) and
malaria now occur in epidemic form almost on an annual basis causing
considerable morbidity and mortality. Dengue is spreading rapidly to newer
areas, with outbreaks occurring more frequently and explosively. Chikungunya
has re-emerged in India
after a gap of more than three decades affecting many states.
An increase in temperature, rainfall and humidity in some
months in the Northwest Frontier Province of Pakistan has been associated with
an increase in the incidence of P. falciparum malaria. In north-east
Punjab, malaria epidemics increase fivefold in the year following an El Niño
event, while in Sri Lanka
the risk of malaria epidemics increases fourfold during an El Niño year. In
Punjab, epidemics are associated with above-normal precipitation, and in Sri Lanka , with
below-normal precipitation.
According to WHO, many countries in Asia
experienced unusually high levels of dengue and/or dengue haemorrhagic fever in
1998, the activity being higher than in any other year. Changes in weather
patterns, such as El Niño events, may be major contributing factors, since
laboratory experiments have demonstrated that the incubation period of dengue 2
virus could be reduced from 12 days at 30 °C to 7 days at 32–35 °C
in Aedes aegypti .
Public health officials often use the term tropical diseases
to refer collectively to a list of infectious diseases that are found primarily
in developing countries. These include malaria, schistosomiasis, dengue,
trypanosomiasis, leprosy, cholera, and leishmaniasis, among others. Many of
these diseases are spread by insect vectors, and all of them disproportionately
affect the world's poor. Malaria is the most severe of these, with the World
Health Organization estimating that the disease causes about 250 million
episodes of acute illness and perhaps 880,000 deaths annually.
The most widespread and severe climate-sensitive
vector-borne disease in South America is malaria.
Studies have shown that unusually dry conditions (for example, those caused by
weather related to the El Niño–Southern Oscillation phenomenon in the northern
part of the continent) are accompanied or followed by increases in the
incidence of the disease. This has been documented in Colombia and Venezuela .
In Asia, dengue fever
and malaria have been associated
with positive temperature and rainfall anomalies, while in Australia arboviral disease
outbreaks are most frequently associated with flooding. Urban developments in Asia and the surrounding regions may have a substantial
impact on trends in the transmission of dengue fever. In some areas, such as Viet Nam ,
effects of past civil instability and slow economic growth may also be
implicated.
Climate change would directly affect disease transmission by
shifting the vector's geographic range and increasing reproductive and biting
rates and by shortening the pathogen incubation period. Climate-related
increases in sea surface temperature and sea level can lead to higher incidence
of water-borne infectious and toxin-related illnesses, such as cholera and
shellfish poisoning. Human migration and damage to health infrastructures from
the projected increase in climate variability could indirectly contribute to
disease transmission. Human susceptibility to infections might be further
compounded by malnutrition due to climate stress on agriculture and potential
alterations in the human immune system caused by increased flux of ultraviolet
radiation.
Of the many scientists who have projected, predicted and
warned of the likely health effects of climate change, almost all agree on the
basics: they will be widespread and unpredictable, they are likely to be
severe, and many, many people across the world will die as a result.
New Scientist magazine reported that ‘human disease is
emerging as one of the most sensitive, and distressing indicators of climate
change. “It is accepted by virtually all climate scientists that the likely
increase in and spread of, potentially fatal diseases is likely to be the
single most dangerous threat that climate change poses to human health.
Among the ten most dangerous diseases Malaria is the world’s
most prevalent mosquito- borne disease. All experts seem to agree that one effect
of climate change will be to increase the range of the malarial mosquito. Destruction of
forests to create new human settlements can increase local temperatures by 3–4
°C and at the same time create breeding sites for malaria vectors. These
phenomena can have serious consequences on malaria transmission in India , African
highlands and other parts of the world.
And it is not just vector-borne diseases that are likely to
take advantage of the changing climate. Other infectious killers are likely to
enjoy a resurgence too, particularly diseases associated with water supply and
sanitation. Climate change could have a major impact on water resources and
sanitation by reducing water supply. This could in turn reduce the water
available for drinking and washing, and lower the efficiency of local sewerage
systems, leading to increased concentration of pathogenic organisms in raw
water supplies.
More than 100 pathogens can cause illness if you drink or
swim in water contaminated by sewage, including norovirus Norwalk and hepatitis A viruses and bacteria
such as E. coli and campylobacter.
Several studies have shown that shifts brought about by
climate change make ocean and freshwater environments more susceptible to toxic
algae blooms and allow harmful microbes and bacteria to proliferate.
Global Warming will also increase rainfall intensity. Rainfalls will be heavier, triggering sewage overflows, contaminating drinking water and endangering beachgoers. Higher lake and ocean temperatures will cause bacteria, parasites and algal blooms to flourish. Warmer weather and heavier rains also will mean more mosquitoes, which can carry theWest Nile virus, malaria and dengue
fever. Fresh produce and shellfish are more likely to become contaminated.
Global Warming will also increase rainfall intensity. Rainfalls will be heavier, triggering sewage overflows, contaminating drinking water and endangering beachgoers. Higher lake and ocean temperatures will cause bacteria, parasites and algal blooms to flourish. Warmer weather and heavier rains also will mean more mosquitoes, which can carry the
Heavier rainfalls are one of the most agreed-upon effects of
climate change. The frequency of intense rainfalls has increased notably in the
Eastern India, China , Philippines , Korea
and Japan .
Flooding may follow heavy rainfall. For developing nations
there is evidence of outbreaks following floods. Outbreaks of leptospirosis in Rio de Janeiro (Barcellos and Sabroza 2001) and in the Philippines (Easton 1999) have followed floods. Hepatitis
E, malaria and diarrhoeal disease have followed floods in Khartoom (Homeida et
al. 1988; Novelli et al. 1988 ). Both acute diarrhoea and acute
respiratory disease increased in Nicaragua following Hurricane Mitch
and the associated flooding (Campanella 1999).
Temperature can affect both the distribution of the vector
and the effectiveness of pathogen transmission through the vector. Gubler et al. (2001) list a range of possible mechanisms
whereby changes in temperature impact on the risk of transmission of
vector-borne disease:
- Increase or decrease in survival of vector
- Changes in rate of vector population growth
- Changes in feeding behaviour
- Changes in susceptibility of vector to pathogens
- Changes in incubation period of pathogen
- Changes in seasonality of pathogen transmission
By 2100 it is estimated that average global temperatures
will have risen by 1.0–3.5 °C, increasing the likelihood of many vector-borne
diseases in new areas. The greatest effect of climate change on transmission is
likely to be observed at the extremes of the range of temperatures at which
transmission occurs. For many diseases these lie in the range 14–18 °C at the
lower end and about 35–40 °C at the upper end. Malaria and dengue fever are
among the most important vector-borne diseases in the tropics and subtropics;
Lyme disease is the most common vector-borne disease in the USA and Europe .
Encephalitis is also becoming a public health concern. Health risks due to
climatic changes will differ between countries that have developed health
infrastructures and those that do not.
Human settlement patterns in the different regions will
influence disease trends. While 70% of the population in South America is
urbanized, the proportion in sub-Saharan Africa
is less than 45%. Climatic anomalies associated with the El Niño–Southern
Oscillation phenomenon and resulting in drought and floods are expected to
increase in frequency and intensity. They have been linked to outbreaks of
malaria in Africa, Asia and South America .
Climate change has far-reaching consequences and touches on all life-support
systems. It is therefore a factor that should be placed high among those that
affect human health and survival.
Conclusion:
Analyzing the role of climate in the emergence of human
infectious diseases will require interdisciplinary cooperation among
physicians, climatologists, biologists, and social scientists. Increased
disease surveillance, integrated modeling, and use of geographically based data
systems will afford more anticipatory measures by the medical community.
Understanding the linkages between climatological and ecological change as
determinants of disease emergence and redistribution will ultimately help
optimize preventive strategies.
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Barcellos, C. and Sabroza,
P.C. (2001) The place behind the case: leptospirosis risks and
associated environmental conditions in a flood-related outbreak in Rio de Janeiro . Cadernos
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Bouma MJ, Dye C, van der Kaay HJ. (1996) Falciparum
malaria and climate change in the northwest frontier province of Pakistan
Bouma MJ et al. (1997) Predicting high-risk years for malaria in Colombia
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Campanella, N. (1999) Infectious diseases and natural
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