Ticks therefore solely rely on a host animal for food while production of the host animal is heavily reduced and in severe cases fatalities happen.
In Zimbabwe, tick-related problems are mostly seen during the rainy season while isolated cases may be recorded in winter months. This has prompted farmers to put more attention to tick control during the summer months from November to May, with little attention during the rest of the year. Tick control programmes implemented on the farm must take cognisance of tick developmental stages and formulate a continuous integrated approach year round.
With unrestricted movement of animals throughout the year and unavailability of paddocks and fences, animals tend to play a major vector role in spreading ticks across plots and farms.
During winter months, when animals are freely moving and ticks are at their early developmental stages, animals do not carry the alarming engorged ticks implying that they can go for long periods without notice.
Ticks undergo development in four stages of their life cycle: egg, the six-legged larva, eight-legged nymph and adult ticks. Larvae and nymphs change to the next stage after digesting blood from a host animal and this normally happens during winter months.
Most of the ticks have a three-host life cycle, whereas each of the three active stages feed on a different host animal. Larvae feed on one animal, drop to the ground and moult to a nymph. The nymphs must attach to another animal, engorge, drop to ground and moult to an adult. The adult tick feeds on a third animal. An engorged (blood-fed) female tick will produce a single large batch of above 1 000 eggs and then die. Control of this cycle is mostly emphasised on the “visible” engorged tick during the summer months.
The larvae and nymphs generally feed on small to medium-sized hosts, while adult ticks feed on larger animals.
Larval ticks will be clustered on the egg mass after hatching and when ready to feed, ascend on blades of grass or similar vegetation to wait for a host.
Ticks assume a “questing” position by clinging to the leaf, litter or vegetation with the third and fourth pair of legs. Due to differences in susceptibility to desiccation and host preference, immature ticks generally remain in the low vegetation, while adult ticks may seek a host at a higher level in the vegetation.
Ticks detect their hosts through several host odours (including carbon dioxide, ammonia, lactic acid, and other specific body odours), body heat, moisture, vibrations, and — for some — visual cues like a shadow. Slow moving dairy animals which produce lactic smells are more at risk to ticks in search for hosts. This behaviour of ticks means that they are more prevalent during periods when paddocks are full of grass and bushes. As grass become taller, mature ticks climb to grass tips exposing animals to mature ticks more than nymphs and larvae.
Tick control programmes
Ticks are difficult to control because they use multiple hosts and exhibit four developmental stages making it difficult to thwart them with one method at once. This means that they can either be on the ground as eggs, on the grass waiting for a host or attached to one of the multiple hosts. Tick control programmes normally target the accessible host (cattle). This has its own challenges from drug selection to spraying and dipping techniques. Farmers usually have a preferred drug which is used again and again (sometimes wrongly) until the types of ticks on the farm become resistant to the drugs.
As a rule of thumb, farmers dip cattle weekly in summer and fortnightly in winter. This regime is effective when the choice and use of drug is correct. With high infestations on the farm, reducing the population of ticks is not as easy as following this routine dipping programme. The tendency is to skip or delay dipping in winter because there are no”visible” signs of infestation.
During this period ticks will be on the nymph and larvae stages and isolated cases of tick borne diseases may be diagnosed on the farm. This is because animals are presumed to be “tick free” as the early stages of tick development cannot be seen easily by a naked eye. To reduce tick numbers on the farm it may be worthwhile to run a full winter season on weekly dipping and try to reduce tick levels before reverting to the conventional fortnightly dipping in the next year. This is expensive in the first year but when this approach is implemented together with other management practises of controlling animal movement it proves to be worthwhile.
Several tick control drugs are available for use in Zimbabwe. These are formulated and tested locally and they can buy from reputable manufacturers and suppliers locally. Farmers need to know and understand types of ticks prevalent in their areas to be prepared to avert disease challenges that they are likely to encounter at farm levels. For this and other tick related problems that you may encounter, Windmill (Pvt) Ltd has a team of experts who are dedicated to assist you solve such challenges.
Written By Claude Ndavambi, 0772433496/ firstname.lastname@example.org(Technical Advisor – Windmill Animal Health and Stock Feeds Division)