TEMPERATURE extremes cause ground frost during the cold season and heat waves during the hot season.
Climate change is expected to bring an increase in average temperatures across the country of between 1°C and 3°C.
A moderate decrease in average rainfall is expected.
Rainfall variability and distribution are expected to increase and climate-related hazard events, such as droughts, heat waves, freak storms and cyclones.
In livestock, climate change contributes to immune suppression while accelerating the chance of infections resulting in the potential increased use of antimicrobials.
The increased use of antimicrobials can potentially lead to an increase in antimicrobial resistance (AMR) which is ranked among the current global challenges.
About 7 000 000 people die every year due to AMR, and, by 2050, it is expected rise to 10 million deaths per year.
Medical researchers report a high prevalence of bacteria resistance to most antibiotics including reserve group antibiotics (colistin), demonstrating AMR to be an important and growing issue.
Mastitis is a major health problem in the global dairy industry.
Several studies show that mastitis incidences increase during summer and have a significant correlation with heat stress (HS) due to suppressed immunity, thermal injury of the udder, increased survival capacity and the spread of pathogens in summer.
Heat stress affects the reproductive performance of livestock by changing blood flows and production of different hormones, with reductions of 20-30 percent in conception rates and anoestrus in ruminants during the summer.
Heat stress also impacts semen quality, oestrus cycle, and oocyst and embryo development.
The pig industry suffers due to impaired reproductive disturbances during late summer and early autumn months compared to spring and winter.
It is called seasonal infertility, with pigs influenced by photoperiod and temperature.
A number of studies report increases in animal mortality rate once temperatures range above the average with increased mortality incidence during extreme weather situation.
Temperature increases between 1°C-5°C above average can result in higher mortality in grazing livestock.
There have been many reports on the increase of livestock mortality during extreme weather events.
In France, during the summer of 2003, pigs, poultry, rabbits and over 35 000 people died due to extreme and prolonged heat waves.
In India, increased mortality is reported in sheep during the summer season due to HS.
Mortality rates in livestock also increase significantly during transport and lairage due to HS.
On average, the higher-altitude areas in the north and east of Zimbabwe experience lower temperatures than low-lying areas in the west and south.
The coolest maximum temperatures are experienced in the eastern highlands and the hottest in the low-lying areas in the west and extreme south.
Over the past years, Zimbabwe has recorded dramatic increases in the maximum summer temperatures. Studies from the Meteorological Services Department of Zimbabwe estimate that the minimum temperatures have risen by 2.6°C over the past century.
Meanwhile, annual rainfall has declined by five percent across the country over the same period.
The indirect effect of climate change on livestock health is associated with climate-driven ecosystem changes and physiological adaptations which could trigger vectors or pathogen virulence and/or genome diversity and vector-pathogen-host exposure.
The emergence and re-emergence of vector-borne pathogens globally have provided evidence for the relationship between climate change and effects on the human/animal health interface.
In the disease process, three epidemiological factors, such as the agent, host and environment, are closely intertwined and persist in ecosystems.
Climate change could enhance pathogen replication and/or virulence which can negatively affect livestock health.
The indirect effects of climate change on livestock health include vector-borne pathogen.
Global warming and changes in precipitation and humidity also affect the reproduction and spread of vector-borne pests such as midges, flies, ticks and mosquitoes.
This, in turn, has the potential of increasing the geographic spread of vector-borne diseases such as blue tongue, lumpy skin diseases (LSDs), anaplasmosis, babesiosis and theileriosis.
In 2007, an Intergovernmental Panel on Climate Change (IPCC) report warned that global climate change patterns could affect the spatial distribution of vectors, such as mosquitoes and ticks.
The transmission dynamics of vector-borne diseases could be affected in two ways, including vector survival and geographical range changes and nature of vector activity, efficiency and susceptibility to infectious changes.
Arthropod vectors are very fragile to fluctuations in temperature and humidity.
Several researchers report that warmer conditions accelerate disease transmission into host livestock.
Tick infestation in climate change condition can decrease an animal’s body weight by about 18 percent. A model simulated by Wittmann et al. (2001) demonstrated that in Australian livestock an increase of 2°C in environmental temperature can extensively spread culicoidesimicola, which is responsible for the transmission of the blue tongue virus in sheep, cattle, goats and also wild ruminants.
Facilitated by global warming, this virus has been spreading globally since 1990.
With the current changing weather patterns, blue tongue virus recently spread to Zimbabwe.
Hemoprotozoan infection is an important protozoa health hazard of livestock in tropical countries that can be transmitted by ticks.
As a sub-tropical country, the livestock in Zimbabwe suffer severely from hemoprotozoan infection such as babesia, anaplasma, and theileria.
The overall prevalence in cattle is found to be 50 percent with a breakdown between high-yielding cross-breed cattle (80 percent) and indigenous cattle (22 percent), demonstrating a significantly increased susceptibility in the crossbred cattle.
Tick reproduction is also known to increase during summer seasons as humidity increases to 85 percent as a result of blood protozoa infestation increasing in cattle.
Lumpy skin diseases, which has afflicted cattle in Zimbabwe in recent times, is a vector-borne viral infectious disease of cattle caused by capripoxvirus of the poxviridae family.
The mosquito aedes aegypti acts as a potential vector for LSD transmission in cattle.
Climatic factors can influence the population of aedes mosquitoes.
According to a published report, the density of a. aegypti became 13 times higher in Dhaka City, Bangladesh, during 2019, when an outbreak of LSD in cattle emerged for the first time.
The morbidity rate was recorded as 18,33 percent (66/360) with no associated mortality.
Climate change impacts on vector populations and distribution and, as such, may influence the transmission of LSD and further the risk of spread across a wide geographical area.
An outbreak of LSD is a sign of the continuous influences of climate change on livestock.
Climate change is predicted to have a negative effect on Zimbabwe’s water resources both in terms of the quantity and quality of water available.
This will have a serious negative impact of farming and livestock production, which will become more disease prone.
Dr Tony Monda BSc, DVM, DPVM, is currently conducting veterinary epidemiology, and agro-economic research in Zimbabwe.
For views and comments, email: tonym.MONDA@gmail.com
