Disease Control 3

1. TICKS

There are two well-defined families of these parasites, the Ixodidae species or hard ticks and the Argasidae species or soft ticks and the two groups differ from each other markedly in appearance, habits and life histories. From the veterinary point of view, the hard ticks are by far the more important.

Members of the family Ixodidae have a hard dorsal shield which covers the entire upper surface of the male and a relatively small area just behind the head of a female nymph or larva. This dorsal shield or scutum bears a pattern which is characteristic for each species of tick. Sometimes the scutum is uniform in colour and the pattern is made up only of pits, grooves and minute indentations, but in some ticks, a colour pattern is also present.

LIFE CYCLE

The fully fed female drops off her host and, after a few days, lays a single large batch of several thousand eggs in a crack in the ground. She then dies. After a period of weeks or perhaps months, depending on the species of ticks and also the temperature and humidity, minute 6-legged larvae (pepper- ticks) hatch. These pepper-ticks attach themselves to animals. After feeding for a while there is a period of quiescence while structural changes take place inside the skin of the larva.

When the changes are complete, the larva becomes a nymph which in turn feeds and moults into an adult.

The adults mate and the females drop off to lay their eggs and die. The males remain on the host for weeks or months before they drop off and die.

According to their habits, ixodidae ticks may be divided into three groups:

• One-host ticks

These remain on the same host from the time they attach themselves to it as larvae until they finally drop off as fully-fed adults e.g. Boophilus decoloratus, the Blue Tick.

• Two-host ticks

The larvae attach themselves to a host and moult into nymphae which feed on the same host and then drop to the ground and moult. When adults emerge, they have to find a new host on which to feed e.g. Rhipicephalus evertsi, the Red-legged Tick.

• Three-host tick

These require three different hosts:

• The Larva Stage   – 1 host
  • The Nymph Stage – 1 host
  • The Adult Stage    – 1 host

Most of the Ixodidae family belong to this group, examples being the Brown Ear Tick, Rhipicephalus appendiculatus, and the Tropical Bont Tick, Amblyomma variegatum.

The life cycles of the three types of ticks are shown below.

Figure 1: Life Cycle of the One Host Tick

Figure 2: Life Cycle of the Two Host Tick

Figure 3: Life Cycle of the Three Host Tick

2.    TICK BORNE DISEASES

The following is a list of diseases which are spread by ticks:

DISEASE	SPREAD BY
Heartwater	Bont Tick
Redwater	1 Host, 2 Host or 3 Host Ticks
East Coast Fever	Brown Ear Tick
Gonderiosis Theileriasis	Brown Ear Tick
Corridor Disease	Brown Ear Tick
Anaplasmosis (Gallsickness)	Blue Tick
Sweating Sickness	Bont-legged Tick
Biliary Fever of Horses	Bont Tick, Brown Ear Tick
Cattle Tick Fever	Bont Tick

3.    DIP-RESISTANT TICKS

Throughout Africa ticks have steadily built up resistance to the dips that have been used to control them. The problem of resistance is caused by the irregular and improper use of chemical dips, and many farmers cause the problem on their farms. When ticks develop resistance to a particular dip, this resistance is permanent and is made worse by the fact that there is a resistance to all the other dips made with the same chemical basis. It is most important that the development of resistant ticks should be delayed for as long as possible by the correct and regular use of cattle dip. The dip used in a spray race should be freshly mixed at the correct strength for each dipping.

The dip mixture in a plunge dip should be at the correct strength and should be checked regularly and brought up to strength by adding fresh dip. If ticks become resistant to a dip, the farmer has to change to the next dip up the resistance ladder. Dips at the top of the ladder are much more expensive than those at the bottom.

TICK RESISTANT LADDER

ACTIVE INGREDIENT OF DIP	DATE WHEN RESISTANCE FIRST DETECTED
Fluasuron	–
Invermectines – Injectable	–
Amidines ( Amitraz)	1995
Pyrethroids	1987
Carbonates	1967
Organophosphates	1967
*Toxoplan (Toxaphene)	1950
*BHC	1952
*DDT	1950
*Arsenic   *No longer on the market	1941

• Ivermectines are injectable only, and are only registered for blue tick control.
  • Fluasurons (Acatak and Deadlin Extreme) are only available as a pour-on and are very effective against ticks.
  • Amidines (Amitraz and Cymiazol), Pyrethroids, Carbonates and Organophosphates are all available for plunge dips, sprays or as a pour-on.
  • Organophosphates were very effective against ticks, but there is widespread resistance to them by ticks, especially blue ticks. They are now used mainly in combination with other dips.
  • Pyrethroids – resistance by ticks developed quickly, but they are still very good for  fly control.
  • Amidines are very good against ticks, causing detachment of the ticks, No effect against flies. Some resistance is developing.

4.       SITE SELECTION FOR A DIP

A few hints on site selection particularly where a new dip is installed because so often the incorrect sites are selected and there is very little which can be done afterwards.

Special consideration should be given to the following:

• There must be an abundant supply of water;

• The dip must be conveniently situated in relation to the paddock;

• The approaches must be on hard ground otherwise the surrounding vegetation will be destroyed, resulting in soil erosion, a common problem around dips;

• The dip should be situated on relatively high ground to allow for suitable drainage;

• Where the plunge or bath is situated, the entrance and exit should be uphill;

• There are various designs for the layout of the handling facilities around the dip and it is advisable to consult a specialist prior to making final decisions. See the lecture on Beef Cattle;

• The capacity of a plunge dip should be 13 000 to 14 000 litres and, as the bath is being filled from a tank of known capacity, the level of the water should be marked on the wall every 200 litres (using marked with paint);

• Every plunge dip should have a roof for draining off rainwater to the mixture, and also to prevent excess evaporation. This will result in an increase in concentration;

• A special room should be erected in order to store dip and other equipment normally required at the dip;

• Dip strength should be checked regularly and brought to strength prior to every dipping; and

• It should be remembered that the dip and handling facilities are most important in a cattle enterprise and the layout and design must be accurately planned.

Source: upload.wikimedia

Figure 4: Sprayrace for Cattle