Bovine respiratory syncytial virus infection

INTRODUCTION

The deleterious effects of ticks on domestic and wild animals in Southern Africa are well known and have been extensively reviewed in Monograph 1 of this series, and elsewhere. We briefly summarise here the effects of ticks on livestock – including small stock and game animals.

Heavy infestations of certain tick species such as the blue ticks Rhipicephalus (Boophilus) spp. which secrete salivary substances that have an anorectic effect on the host animal, result in significant weight loss or production. This effect is seen especially in exotic cattle breeds, which show better weight gain when tick infestation is controlled. Tampans or soft-bodied ticks which occur in the more arid western areas of the country can cause extreme irritation, blood loss, toxicoses and death in calves and small stock.

Tick species which have long mouthparts such as Amblyomma and Hyalomma cause considerable discomfort as well as tissue damage in cattle, leading to scarring of hides, and damage to testes and the udder which may lead to the loss of teats. These wounds may become secondarily infected with bacteria, resulting in the development of abscesses or fly strike. In small stock, the socalled foot ticks or those which are found around the claws of sheep and goats, either between or around the claws, cause wounds which can lead to secondary infection with resulting lameness. Tick damage due to the long mouthparts of Amblyomma ticks and irritation due to various Rhipicephalus spp. such as brown ear ticks, cause problems in susceptible species. Eland and gemsbok may lose ears due to necrosis with secondary myiasis. Heavy infestations on the eyelids can cause eye irritation, with subsequent infection. Abscesses may be seen in cattle and various antelope and other game species due to secondary infection of wounds caused by ticks.

Some tick species have strains which secrete toxic substances in the saliva, which can cause a variety of syndromes; some tick toxins cause paralysis in cattle and small stock (spring lamb paralysis, Karoo paralysis, angora kid paralysis). A different toxin found in Hyalomma truncatum causes dermatosis and immune suppression in calves, called sweating sickness, and which can lead to fatalities. Advanced cases may be irreversible – even if the ticks have been removed. Angora goat kids develop a paralysis on exposure to heavy burdens of Rhipicephalus warburtoni, which cluster inside the ears of newborns.

Certain tick species are the vectors of various bloodborne organisms, including Rickettsia ruminantium, Babesia spp., and Anaplasma marginale. The Theileria infection known as corridor disease, and which is harboured in African buffalo, still remains a threat in KwaZulu-Natal if ticks infected with Theileria mutans infect cattle farms adjoining the Hluhluwe/Umfolozi parks. Other Theileria spp. can cause severe losses in game animal species such as roan and sable (see Monograph 3). Many of these tickborne diseases cause fatal infections and/or considerable economic loss.

Domestic ruminant livestock are susceptible to heartwater, and the disease is transmitted by Amblyomma hebraeum. It affects cattle in the wetter parts of the country, and is a very big problem in some commercial sheepand goat-farming areas like the Eastern Cape.

Tick conditions seen in cattle

Figure 1 Severe tick damage due to brown ear ticks often causes secondary myiasis and ear loss.

Figure 2 Sweating sickness is a dermal toxicosis seen in calves.

Figure 3 Cerebral babesiosis causes severe congestion of the brain.

Figure 4 Heavy tick burdens cause “tick worry” which results in appetite suppression and weight loss.

Tick conditions in small stock

Figure 5 Foot abscess in small stock is caused by primary damage by ticks.

Figure 6 Karoo paralysis is a tick toxicosis caused by Ixodes rubicundus.

Figure 7 Severe tick infestation with foot ticks can cause lameness in small stock.

Figure 8 Heartwater in small stock is a severe problem in certain areas.

Selection of tick control methods in livestock and game

Deciding what tick control strategy to use in South Africa is complex, because of the many factors involved: the host species, the species of tick, the predominant tick-borne diseases, and the type of farming.

Part 1 is dedicated to a general discussion of tick control methods, as well as a summary of the problems of tick-borne diseases. Acaricides are still the mainstay of tick control in animal health, and therefore much of this section is dedicated to their use, management, efficacy and resistance. In the absence of a specific tick vaccine for South African conditions, acaricides will continue to be used as the main control measure – but need to be used judiciously to maximise their useful life.

Part 2 presents a brief discussion of tick-borne diseases, which will be dealt with in much more detail in Monograph 3 of the series.

Part 3 approaches tick control methods based on the main target tick species, because of the very different conditions and also the different tick-borne diseases. In livestock the authors adopt a geographic approach based on the distribution of tick species and the tick-borne diseaseswhich occur in various parts of South Africa.

GENERAL TICK CONTROL METHODS

ACARICIDES

For an overview of the history of acaricide use in South Africa, see Monograph 1 of this...

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