30
a mammalian host. These include vector-borne diseases, helminthoses and fungal
infections.
Indirect effects are less apparent and would include changes in disease transmission patterns associated with climate-induced ecological, socio-cultural or behavioural disruptions. In pastoral areas, for example, prolonged droughts trigger more
frequent and long-distance movements which enhance contact between distinct
populations of animals. This would also include movement into previously uninhabited areas potentiating exposure to new disease agents. Different indirect effects
are reviewed in Lindahl and Grace (2015).
We use two well-studied vector-borne diseases—Rift Valley fever, which often
occurs in epidemics in East Africa, and tick-borne diseases, which are endemic in
many parts of the world—to demonstrate the impacts of climate change on livestock
diseases. Our review focuses on the direct effects given that indirect effects are not
well studied and are also difficult to quantify.
3.2 Case Studies
3.2.1 Rift Valley Fever
Rift Valley fever (RVF) is a mosquito-borne viral zoonosis mainly affecting sheep,
goats, cattle, buffaloes and camels. People become infected following a bite from an
infected mosquito, or after close contact with acutely infected animals or infected
tissues. In people, the disease manifests as a mild influenza-like syndrome in a
majority of cases (more than 80%) or a severe disease with haemorrhagic fever,
encephalitis, or retinitis in a few cases (Njenga et al. 2009). In livestock, the disease
manifests as increased abortion and perinatal mortality rates.
3.2.1.1 Drivers
RVF outbreaks have been reported in some countries in East and southern Africa
including Kenya, South Africa, Tanzania and Uganda following periods of abovenormal precipitation. The disease has also been reported in other countries including the Comoros archipelago, Madagascar, Mauritania, Saudi Arabia, Senegal and
Sudan (Madani et al. 2003) and Yemen (Abdo-Salem et al. 2006). In South Africa,
recent RVF outbreaks observed in 2008–2011 were associated with relentless and
widespread strong seasonal rainfall and high soil saturation (Williams et al. 2016).
Areas affected by these outbreaks are shown in Fig. 3.1. In East Africa, major outbreaks are often associated with the warm phase of the El Niño/Southern Oscillation
(ENSO) phenomenon, although there have been a few incidences (e.g. in mid-1989)
when an elevated RVF activity was not ENSO-driven. There have also been localised outbreaks in Uganda associated with seasonal rainfall and flooding. Figure 3.2
B. Bett et al.
a mammalian host. These include vector-borne diseases, helminthoses and fungal
infections.
Indirect effects are less apparent and would include changes in disease transmission patterns associated with climate-induced ecological, socio-cultural or behavioural disruptions. In pastoral areas, for example, prolonged droughts trigger more
frequent and long-distance movements which enhance contact between distinct
populations of animals. This would also include movement into previously uninhabited areas potentiating exposure to new disease agents. Different indirect effects
are reviewed in Lindahl and Grace (2015).
We use two well-studied vector-borne diseases—Rift Valley fever, which often
occurs in epidemics in East Africa, and tick-borne diseases, which are endemic in
many parts of the world—to demonstrate the impacts of climate change on livestock
diseases. Our review focuses on the direct effects given that indirect effects are not
well studied and are also difficult to quantify.
3.2 Case Studies
3.2.1 Rift Valley Fever
Rift Valley fever (RVF) is a mosquito-borne viral zoonosis mainly affecting sheep,
goats, cattle, buffaloes and camels. People become infected following a bite from an
infected mosquito, or after close contact with acutely infected animals or infected
tissues. In people, the disease manifests as a mild influenza-like syndrome in a
majority of cases (more than 80%) or a severe disease with haemorrhagic fever,
encephalitis, or retinitis in a few cases (Njenga et al. 2009). In livestock, the disease
manifests as increased abortion and perinatal mortality rates.
3.2.1.1 Drivers
RVF outbreaks have been reported in some countries in East and southern Africa
including Kenya, South Africa, Tanzania and Uganda following periods of abovenormal precipitation. The disease has also been reported in other countries including the Comoros archipelago, Madagascar, Mauritania, Saudi Arabia, Senegal and
Sudan (Madani et al. 2003) and Yemen (Abdo-Salem et al. 2006). In South Africa,
recent RVF outbreaks observed in 2008–2011 were associated with relentless and
widespread strong seasonal rainfall and high soil saturation (Williams et al. 2016).
Areas affected by these outbreaks are shown in Fig. 3.1. In East Africa, major outbreaks are often associated with the warm phase of the El Niño/Southern Oscillation
(ENSO) phenomenon, although there have been a few incidences (e.g. in mid-1989)
when an elevated RVF activity was not ENSO-driven. There have also been localised outbreaks in Uganda associated with seasonal rainfall and flooding. Figure 3.2
B. Bett et al.