Livestock production plays an essential role in the development and growth of economies in African countries
(Undi et al., 2006). In developing countries, livestock animals are kept as assets to generate income and provide food security for approximately 60-80% of the rural communities
(Smit et al., 2013). Ghil and Lucarini (2020) defined climatic variability as the climatic parameter of an area changing from its long-term mean due to natural internal processes inside the climatic system and from differences in external forces (anthropogenic and natural). Ruminants are severely affected by climatic variabilities, resulting in increased susceptibility to diseases.
Ali et al. (2020) stated when ruminant animals are exposed to high temperatures, feed intake is reduced while respiration and sweating rates increase.
Rocklov and Dubrow (2020) reported that climatic variabilities affect the re-emergence of vector-borne diseases, the dynamics and rate of transmission and the geographic spread of the diseases through various ways that involve the pathogen, the vector and the animal. Additionally,
De et al. (2022) reported that climatic variabilities promote habitat patterns, reproduction and spread of vectors such as ticks, flies, midgets and mosquitoes.
Chepkoech et al. (2018) reported that in recent years, climate change has resulted in adverse variabilities such as extremely hot or cold temperatures and prolonged periods of drought and floods. According to Office International des Epizootic (2014) the scarcity of water caused by drought spells typically changes the hygiene habits and quality of water and that might increase the occurrence of viral diseases mostly in arid and semi-arid areas.
Filipe et al. (2020) observed that a rise in ambient temperatures typically results in reduced feed intake because the hypothalamic appetite centre of farm animals is affected.
Matope et al. (2020) added that the occurrence of ruminant diseases and associated mortalities is common in sub-Saharan Africa following extreme droughts and periods of heat stress.
Ekine-Dzivenu et al. (2020) stated that when lactating animals are subjected to high ambient temperatures and humidity for long periods, their ability to regulate heat that is generated from both the environment and metabolic processes decreases and thus results in decreased milk production. There is a need to determine the extent to which ruminant diseases are influenced by temperature and rainfall variabilities so that the adverse effects of climate change can be reduced by developing control and management practices in accordance to disease prevalence.
The information provided in this review was acquired from the articles that were published from the year 2006 to 2022. Electronic data sources such as Google scholar, Rsearch gate, Link springer and Science direct were accessed to retrieve the articles. The keywords “climatic factors”, “occurrence”, “ruminant diseases” and “pathogens” were used in the search process.
The effects of temperature and rainfall variabilities on the immune statuses of ruminants
Chauhan et al. (2021) pointed out that the role of the immune system is to protect the host from invasive pathogenic organisms through its complex mechanisms however, according to
Lacereta (2019), environmental extremities such as heat stress impair immune responses.
Chen et al. (2018) highlighted that the effects of heat stress can be direct or indirect while severity of the effects depends on the amount of time an animal is exposed to heat and animal factors such as the species, breed, sex and age. According to
Ali et al. (2020), when the immune system of an animal is affected, unfavourable conditions take place such as an increase in the occurrence of infections and the reduction in production efficiencies.
Livernois et al. (2021) reported that prolonged exposure to heat stress results in depressed lymphocyte levels and the reduction of vaccination efficacy. Furthermore, high temperatures weaken the functionality of neutrophils, which usually play a major role in protecting mammary glands from infections
(Bagath et al., 2019).
Description of ruminant vector-borne diseases and their occurrences in relation to climatic variabilities
Ticks are described as hematophagous ectoparasites that infest ruminants and other domesticated animals, wildlife and human beings. Ticks are the vectors of tick-borne diseases which are highly prevalent in tropical and subtropical areas in the world (
Twana and Harun 2022). This makes them a public health and veterinary concern because they are responsible for financial and livestock loses
(Boularias et al., 2020). Ticks are categorized into three families known as
Argasidae,
Ixodidae and
Nuttalliellidae. Soft ticks (
Argasidae ticks) thrive well in hot areas that are very dry and have desert-like conditions. They have the ability to resist desiccation which assist their expansion amid climatic variabilities
(Adenubi et al., 2018). Hard ticks (
Ixodidae ticks) suck the blood of mammals, reptiles, avians and amphibians (
Martinez-Garcia et al., 2021). These ticks are known to thrive in warm environments with high humidity. The
Nuttalliellidae family consists of one tick species (
Nuttalliella Namaqua) and shares the same characteristics with both the
Ixodidae and
Argasidae ticks (
Twana and Harun 2022).
Anaplasmosis (Gall sickness)
Anaplasmosis is a tick-borne disease affecting ruminants and caused by
Anaplasma marginale, which is a gram-negative obligate intracellular bacterium that parasitizes erythrocytes
(Ashraf et al., 2021). Mubashir et al. (2022) reported that cattle anaplasmosis is transmitted by at least twenty tick species, however, the main transmission agent is
Rhipicephalus (Boophilus) microplus (
De Almeida et al., 2022). The occurrence of the disease is dependent on the growth and survival of the tick population. The tick consists of parasitic and non-parasitic phases in the one-host life cycle. The non-parasitic phase begins soon after the feeding stops and engorged females drop off the host so to oviposit in the environment
(Yogeshpriya et al., 2022). This phase involves periods of pre-ovipositional and oviposition in engorged females, the incubation and hatching of eggs and larvae seeking a host
(Marques et al., 2020). The population growth and survival of
Rhipicephalus microplus is largely dependent on the environmental temperatures, vegetation habitats and host availability in an area
(Leal et al., 2018). Areas with average temperatures above 17°C can cause the population dynamics of the tick to differ from two to five generations in a year. Furthermore,
Oshiro et al. (2021) reported that oviposition in engorged females’ initiates when temperatures are above 28°C and when temperatures are around 4°C oviposition delays.
Babesiosis (Red water)
Bovine babesiosis is a widespread tickborne disease caused by parasites of the genus Babesia with the most common species being
B. bovis,
B. divergens and
B. bigemina (Zaman et al., 2022). Hard ticks of the family Ixodidae transmit the disease with
Rhipicephalus microplus as the principal vector of the parasites
(Jacob et al., 2022). Clinical signs of babesiosis are high fever, anorexia, anaemia, depression and splenomegaly
(Suarez et al., 2019). Gray (2021) stated that the occurrence and prevalence of the disease depends on the abundance of the ticks. Babesiosis is commonly reported during the summer and autumn seasons
(Ferreira et al., 2022). Abdullah et al. (2019) reported that extreme variations of climatic factors such as temperature and humidity promote the survival, growth and activity of ticks, however, high rainfall patterns were reported to negatively affect the abundance and survival of tick larvae
(Ahmad et al., 2023).
Theileriosis (East Coast fever)
Chen et al. (2021) defined theileriosis as a disease transmitted by ticks and caused by an obligate intracellular protozoan parasite called
Theileria. Globally,
Theileria annulata and
Theileria parva have been reported to be the major species causing the disease
(Dhaygude et al., 2021). Ixodid ticks are responsible for the transmission of the disease and have a complex life cycle in vertebrates (
Dadhich et al., 2017). Symptoms of the disease include fever, anaemia, reduction in milk production, weakness and lethargy
(Agina et al., 2020). According to
Khawale et al. (2019), extreme variations in temperature and humidity create an ideal environment for the abundance of ticks and thus the occurrence rate of the disease is higher during summer months.
Ehrlichiosis (Heart water)
Ehrlichiosis also known as cowdriosis or heartwater is an infectious and acute tick-borne disease caused by a gram-negative obligate intracytoplasmic bacterium called
Ehrlichia ruminantium which belongs to the
Rickettsiales order
(Basit et al., 2022). Ticks responsible for the transmission of the bacterium belong to the genus
Amblyomma, specifically the species
Amblyomma hebraeum and
Amblyomma variegatum.
Garcia et al. (2022) reported that after disease transmission, cattle display clinical signs such as muscle twitching, walking difficulties, anaemia, high fever and disorientation.
Ghafar et al. (2020) reported that just like other tickborne diseases, the occurrence of ehrlichiosis is high during the summer seasons mainly because of favourable conditions created by high average temperatures and high humidity.
Rift valley fever
Rift valley fever is a disease that affects both humans and ruminant animals and caused by an arbovirus of the genus
Phlebovirus, family
Bunyaviridae (Javelle et al., 2020). Disease transmission in animals takes place following the bite of an infected mosquito and in humans it takes place following contact with infected animals and animal products
(Petrova et al., 2020). Rift valley fever is usually associated with abortions. Rift valley fever is typically associated with occasional epidemics caused by an increase in the emergence of floodwater mosquitoes after an area experiences heavy rainfall. Table 1 presents an overview of the occurrence of vector-borne diseases in relation to climatic variabilities in some southern African countries.
Description of infectious, non-vectored diseases of ruminants and their occurrences in relation to climatic variabilities in some southern African countries
Anthrax
Anthrax is primarily a disease of domestic and wild ruminants and is caused by
Bacillus anthracis, a Gram-positive and spore forming bacterium
(Islam et al., 2021). Constable et al. (2022) reported that environmental temperatures between the ranges of 12-42°C promote rapid sporulation of the bacterium. Similarly, higher occurrence rates have been reported in areas that experience heavy rainfall following prolonged drought conditions, dry summer months or after prolonged dry seasons with warm climates
(Alam et al., 2022). Bacillus anthracis spores are usually present in the top layers of alkaline soils with high compositions of organic matter and calcium. The spores remain dormant in the soil during unfavourable climatic and environmental conditions for prolonged periods until the conditions become favourable and sporulation takes place
(Pittiglio et al., 2022). The disease is transmitted when grazing animals ingest contaminated forage and inhale spores. Dead animals transmit the vegetative bacilli through their discharges thereby contaminating the surrounding soil and water sources (
Bakhteeva and Timofeev, 2022).
Foot and mouth disease
Foot and mouth disease is a highly contagious disease affecting cloven hoofed animals. The disease is caused by a virus of the genus
Aphthovirus from the family
Picornaviridae (Baro et al., 2019). Foot and mouth disease is transmitted when an animal has direct contact with a contaminated environment and when virus particles are inhaled following direct contact between infected and non-infected animals
(Paton et al., 2009). The survival and occurrence of the virus is highly influenced by the environmental and climatic factors of an area. Naganayak
et al. (2022) reported that foot and mouth disease virus is genetically unstable and that results in its genome evolution being largely influenced by the mutation pressure. Climatic and environmental conditions have a substantial effect on the mutation pressure. The virus can survive for longer periods in areas where the relative humidity is above 55% and temperatures are below 50°C
(Colenutt et al., 2020).
Mastitis
Mastitis is an infectious disease affecting udder tissue and results in inflammation of mammary glands. The disease is caused by various classes of microorganisms with bacteria such as
Staphylococcus aureus,
Escherichia coli and
Streptococcus uberis being the commonly isolated pathogens
(Cobirka et al., 2020). Fukushima et al. (2020) reported that mastitis is characterised by an increase in the somatic cell count of the tissues of the udder and milk. Clinical signs of the disease include a swollen, red, painful and hot udder, permanent blockage of milk ducks and reduced milk production
(Abdalhamed et al., 2018). Factors that collectively influence the occurrence of mastitis in cattle herds include biosecurity measures, lactation stage, parity and the season
(Smit et al., 2013). Chen et al. (2022) reported high occurrences of mastitis high during the summer rainfall seasons. According to
Dado-Senn et al. (2018), mastitis occurs because of the immune systems’ response to the invasion of bacteria in the teat canal which is common during the summer seasons.
Lumpy skin disease
Lumpy skin is caused by a brick shaped enveloped virus belonging to the family Poxviridae (
Gumbe, 2018). The disease is transmitted through the bite of arthropod vectors namely flies, ticks and mosquitoes. Another transmission route takes place when calves suckle milk from infected dams and when animals share feeding and watering points that are contaminated by saliva and nasal secretions
(Issimov et al., 2022). According to
Choudhari et al. (2020) clinical signs of the disease include nasal discharges, salivation; fever of 40-41°C, lacrimation and lameness. In severe cases, the disease causes infertility in both males and females. Lumpy skin disease has been reported in difference countries around the world.
Das et al. (2021) reported that the disease is more prevalent in areas with humid and warm climates since these environmental conditions create ideal conditions for the growth and development of ticks, mosquitoes and flies hence the disease usually occurs in wet seasons. Table 2 presents an overview of the occurrence of infectious, non-vectored diseases in relation to climatic variabilities in some southern African countries.
