Nufarmer Africa
Detect HEARTWATER early in cattle to prevent losses
Heartwater is a tick-transmitted disease of cattle, sheep and goats as well some wildlife ruminants. The disease is generally characterized by high fever, nervous signs, accumulation of fluid around the heart( hence the name Heartwater), in thoracic cavity, lungs and brain.
The disease occurs in nearly all sub-Sahara Africa where Amblyomma ticks( Bont Ticks) are found and the surrounding islands such as Madagascar, Reunion, Mauritius, the Comoros, Sao Tomé and some islands in the Caribbean.
Based on the records from Centre for Agriculture and Biosciences International( CABI), for the Southern Africa Development Community( Angola, Botswana, Malawi, Mozambique, South Africa, Swaziland, Tanzania and Zimbabwe), the economic losses due to the disease are estimated around 47.6 million of US dollars per year.
Significant losses are due to mortality, diminution of productivity in farming systems and cost of treatment( use of antibiotics and acaricides). Currently, there is lack of data on the socio-economic impact of the disease at household level. However, recent surveys conducted by socio-economists from Agricultural Research Council( ARC) and Human Science Research Council( HSRC) on livestock disease experienced by communal farmers in five provinces of South Africa have revealed Heartwater to be among the disease of economic importance.
Heartwater occurs only where its vectors( ticks) are present and there are various Amblyomma ticks that are capable of transmitting the disease in Africa. Amblyomma hebraeum and Amblyomma variegatum( figure 2 & 3) are major tick vectors of heartwater in the sub-Sahara Africa.
Tick distribution Amblyomma variegatum, known as tropical bont tick, has the widest distribution in Africa and is the only Amblyomma species of African origin that has established itself successfully outside the continent. It is widely distributed through West, Central, North-East and East Africa and in southern Africa extends into Zambia, north-eastern Botswana, the Zambezi Region( formerly the Caprivi Strip) of Namibia, north-western Zimbabwe and central and northern Mozambique. South African bont ticks( Amblyomma hebraeum), are found in moist and warm, bushy areas and does not survive in open grassland.
In South Africa it is found along the coastal belt from Port Elizabeth in the Eastern Cape Province, through KwaZulu-Natal and across Mpumalanga, Gauteng, Limpopo and North-West Provinces, north of a line running approximately through Pretoria to the Botswana border. It is also present in eastern Swaziland, southern Mozambique, eastern
Figure 1: Distribution of Heartwater diseases, CABI 2017
Figure 2: Amblyomma hebraeum, Female( left) and male( right).( Photos: Heloise Heyne)
Botswana and in southern and eastern Zimbabwe( Figure 4).
Disease transmission and incidence Bont ticks become infected with the heartwater organism when they feed on an infected animal. Heartwater develops after an infected tick has fed on a susceptible animal. After the larval and nymphal stages of bont ticks have fed on the host and become engorged, they drop onto the ground, moult( grow and change) into the next stage within 4-6 weeks and then seek new host. The ticks will then transmit heartwater organisms to the next host during feeding.
The incidences vary according to the abundance and activity of ticks. The disease is less frequent during winter months and more frequent during wet season with the increase in the activity of vector ticks. In certain areas, where the environmental conditions are favorable for ticks, the disease may be encountered throughout the year. The movement of animal carrying infected ticks into, or through an area / farm free of the disease can lead to losses amongst susceptible livestock. This occurs through tick feeding on the susceptible livestock by infected ticks which would have dropped from the introduced infected animals.
Clinical signs of the disease The incubation period( time between infection and appearance of clinical signs) in naturally infected
Figure 3: Amblyomma variegatum, Female( left) and male( right).( Photos: Heloise Heyne)
cattle may range from 9-29 days( average 18 days) and that of naturally infected sheep and goats range from 7-37 days( average of 14 days). Affected animals have a fever( 40 °-42 ° C), are lethargic( loss of energy), loss of appetite, and lag behind the rest of the flock or herd.
As the disease progresses, the movements become more impeded with high stepping gait that is more pronounced in the front limbs. Breathing becomes gradually more laboured and animals may stand with their heads held low, make constant chewing movements and push against the objects. In the final stages of the disease, the animal goes down; lying on its side with the head pulled back, legs either extended and still or show pedaling movements.
Findings on dead animals are very similar in cattle, sheep and goats but may slightly differ depending on severity of the disease. Varying quantities of fluid accumulate in the chest cavity and heart sac( hence the name of the disease). Lungs are heavy with fluid that oozing from the cut surfaces and white foam( froth) is found in the air passages. Small hemorrhages( bleeding) may be observed in certain organs such as heart muscles, urinary bladder, stomach and intestine linings.
Disease treatment and prevention: Heartwater can be prevented by immunization of calves, lambs or kids, and strategic control of ticks on animals. The only method of immunization( vaccination) against heartwater is the“ infection and
18 Nufarmer Africa | November / December 2017