CLIMATE change is now a global concern due to its multi-dimensional effects and impact on humans, animals, plants and environment.
Deforestation and vegetation clearance also contributes to the ecological imbalance by increasing local temperature and humidity that accelerate the spread of vectors that cause disease outbreaks and compromise environmental health.
A revealing example can be seen in Bangladesh, where, between 1930-2014, a total of 39,1 percent (from 23,140 km2 to 9,054 km2) deforestation has occurred with continued annual deforestation at about 0,77 percent as witnessed in the eight-year period from (2006-2014).
Climatic variability increases the chances of animals and man contracting disease from the environment.
The abundance, prevalence, severity and geographical distribution of helminths has been one of the ecological aberrations caused by climate change.
For example, it has been observed that in general the development rates of free-living larval stage of the haemonchuscontortus have increased in the tropical and sub-tropical regions of the world, in tandem with increased temperatures.
In sheep, this worm sucks blood from the stomach and causes severe anaemia and death.
In a laboratory condition, the development of ascarissuum eggs through enhanced embryonation becomes accelerated when temperatures increase from 25°C to 35°C in a laboratory condition.
Thus global climate change could influence the rapid development of parasites in their invertebrate intermediate hosts like snails.
The life cycle of lungworms is also reliant on weather conditions, increasing in incidence in the summer/autumn rather than the winter season.
Fascioliasis, schistosomiasis and nematodiases including heterakiasis and different trichostrongyliases are the helminth diseases that are mostly influenced by climatic changes.
Climate change equally influences land-use changes, particularly with the development of dams and irrigation schemes for agricultural productivity, which can contribute to a positive impact on livelihoods and nutrition, but can also have substantial negative effects on human and animal health.
Stagnant water bodies from these systems result in higher localised humidity that can trigger the development of a range of pests and disease vectors.
In Egypt, Sudan and Mauritania/Senegal Rift Valley, Tanzania and the low-lying humid areas of Zimbabwe, fever outbreaks reportedly occurred in livestock grazing in the proximity of dams and irrigated areas.
Other parasitic diseases like trematodiases (fascioliasis and schistosomoses) became endemic in these areas due to torpid water masses and increased humidity which influences the development rates of intermediate hosts (snails) and cercariae.
An increased incidence of fascioliasis in animals occurring in an irrigation area in the Punjab Province of Pakistan was reported.
A similar study was conducted in Tanzania, where I chaired research with a delegation of international OIE veterinary epidemiologists including Dr G. Charters, Dr F. J. Mutua and Dr F. Allens and confirmed that fasciola gigantica and paramphistomes in cattle were higher in irrigation areas than non-irrigation areas and were notably absent in non-grazing areas.
Most of the roughage and concentrate feeds for livestock are perishable in the environment.
The altered environmental temperature and humidity, due to climate change, can directly affect livestock feed quality and consistency of the nutrients ingredients, affecting the growth of moulds in feed.
The growth of moulds and association of mycotoxins production are closely related to temperature and degree of moisture, which are dependent on weather conditions during harvest and techniques used for drying and storage.
The major mycotoxins are aflatoxin, ochratoxin, T2, fumonisin and zearalenone, which are a metabolic product of mycotoxicogenic moulds produced at the optimum temperature of 25°C-37°C and moistures of 80-85 percent.
Mycotoxicogenic moulds can cause acute diseases when an animal consumes above the critical level of contaminated feeds. This can have a negative effect on different organs such as the liver, kidney, gastrointestinal tract and reproductive tract.
The chronic exposure to these mycotoxins, even at low levels, can lead to dangerous immune suppression and reduces production performance and quality of end product.
The aflatoxin type B1 is more toxic and has a significant public health impact due to hepatotoxicity and its carcinogenic properties in humans.
In some countries, about 50 percent of nuts and pulses of livestock are contaminated with aspergillus flavus and contained at least three aflatoxigenic genes, of which 90 percent of them can produce aflatoxin B1 ranging 7-22 µg/g in agar, which are harmful to public health.
For example, traditionally known seasons for disease outbreaks as well as the duration of diseases are often altered by climate change and are extended and spread through pathogen biodiversity as this writer recently noted in Zimbabwe.
Given pathogens cope with the new altered situations, they may cause unhabitual disease outbreaks (out of season diseases), such as the classic example of (January Disease) Theileriosis in Zimbabwe occurring in March or December according to the altered rain season.
It is, therefore, vital to note that one of the most important but overlooked aspects of climate change is that it plays a significant role in disease and pathogen evolution in general.
Temperature and humidity play a substantial role on pathogens that maintain a part of their lifecycle outside the final host body such as those pathogens responsible for black quarter, dermatophiloses and anthrax in livestock.
Anthrax is a deadly zoonotic disease caused by bacillus anthracis spores. This spore can be viable for up to 10-20 years in the soil and pastures. According to WHO, temperature and other climatic conditions, such as humidity, rainfall, pH and water activity of soil and availability of nutrients, all affect the successful germination of anthrax spores. Heavy rainfall, soil erosion and drought may stir up the dormant spores and increase the exposure of an animal to disease.
Global climate change affects the seasonal temperature variation of migratory birds travelling from the Arctic area to tropical and sub-tropical areas such as Zimbabwe.
Evidence exists that during migration, these migratory birds carry and disperse avian influenza virus.
For example, in India they are thought to spread avian influenza virus through contact with local riverside ducks during migration.
The worldwide incidence and intensity of extreme events, such as cyclones, tidal surges, floods and droughts, have increased significantly in recent decades due to global climate warming.
Climate change has influenced average rainfall, evapotranspiration and atmospheric water storage thereby changing precipitation patterns in dry seasons, with downstream impacts on disease distribution, in turn causing diseases in livestock.
In recent years, this has had a significant impact on livestock health and production with many negative consequences, such as nutritional deficiency, lack of fresh water, increased incidence of diarrhoea, skin diseases, liver fluke, loss of bodyweight and breakdown of the immune system. Additional concerns in some countries, including Zimbabwe, include temporal variations to drought and cyclonic characteristics as a result of climate change.
Research has established that changes in global or regional climate patterns due to climate change are affecting livestock health directly and indirectly.
The lingering hot season and increased heat waves in the summer are spiking heat-stress resulting in an increased disease incidence for homoeothermic farm animals.
While efforts are made to grow the livestock sectors in Zimbabwe, to fulfil the increased demand of animal protein for a rapidly growing population in the country, production is, however, hampered by the ignorance of the effects of climate change on agro-veterinary industry.
The crux of the matter is that, with an increased load of emerging and re-emerging infectious animal and zoonotic diseases on the horizon due to climate change and other factors; is Zimbabwe equipped to deal with the holistic approaches required for a healthy climate-proofed population, with a thriving disease-free agricultural livestock sector?
Future climate change in Zimbabwe will cause average temperatures to rise by about 3°C before the end of this century. Annual rainfall predictably could decline by between five and 18 percent, especially in the southern regions.
As rainfall becomes more variable, there will be an increase in droughts, floods and storms.
This will affect Zimbabwe’s food security and pose a threat to human health, energy supply, the livestock industry and the economy.
Specific recommendations for adaptation and mitigation policies, strategies and action on the impact of climate change specifically on human public health and livestock animal health in Zimbabwe is urgently due.
Dr Tony M. Monda BSc, DVM, DPVM, is currently conducting veterinary epidemiology, public health and agro-economic research in Zimbabwe. E-mail: tonym.MONDA@gmail.com