About Ticks – In Cattle

Ticks are not insects, but acarines, their closest relatives are mites, spiders and scorpions. Whereas adult insects have six legs, adult acarines have eight.

Free-living ticks tend not to walk very far. They mostly climb onto vegetation and wait for the next suitable host to come along (Figure 1). All ticks feed on blood during some stage of their life. When a potential host comes near, the waiting ticks become active; they wave their front legs about in what is known as questing behaviour. This is probably triggered by the host animal’s exhaled air (dry ice, which releases CO₂, can be used to attract free-living ticks to traps in the ground).

Whereas 1-host ticks are fairly host-specific (although cattle ticks can be found on goats, hairy sheep, horses, and other animals, they prefer cattle), 2- and 3-host ticks infest animals of a variety of species. The larvae and nymphs will take their blood meal on small ground-dwelling animals or birds. This means that they can be carried over long distances by these intermediate hosts in the absence of any livestock host animals. The bush tick (Haemaphysalis longicornis) and the paralysis tick (Ixodes holocyclus) are 3-host ticks.

Adult ticks’ bodies basically consist of an abdomen, from which protrude the four mouthparts (held closely together, until the tick attaches to take a blood meal), and the eight legs (Figure 2). There is no head and the commonly held belief that the head will break off and remain when the tick is pulled off the host is incorrect.

Kinds of ticks

Ticks can be divided into soft ticks (Argasidae; argasid ticks) and hard ticks (Ixodidae; ixodid ticks). Soft ticks are poorly represented in Australia. It is the hard ticks which are of economic importance to Australian livestock producers. These include the cattle tick (Rhipicephalus australis, previously known first as Boophilus microplus, and then as Rhipicephalus microplus), the bush tick (Haemaphysalis longicornis) and the paralysis tick (Ixodes holocyclus).

Hard ticks can be distinguished by their life cycles into 1-, 2- or 3-host ticks. The cattle tick is a 1-host tick. The bush tick and the paralysis tick are 3-host ticks. The time that an adult tick spends feeding on cattle is determined by its life cycle. Treatment for tick infestations varies depending on the kind of tick present.

Cost and impact of ticks

Ticks cause direct damage to their hosts in a variety of ways.

• Their bite wounds affect the subsequent quality of the leather made from those hides and skins (Image 1).
• The bite wounds can become infected by bacteria, which can lead to complications.
• Fresh tick bite wounds can, in exceptional circumstances, attract flies and lead to flystrike.
• Heavy tick burdens lead to anaemia and loss of live weight.
• Some ticks are toxic, and can cause tissue damage at the site of attachment, or affect the nervous system, as in the case of paralysis tick.
• Ticks can also be indirectly harmful by transmitting diseases such as Anaplasmosis and Babesiosis (jointly known as tick fever in Australia) and theileriosis (bovine anaemia).

The annual cost of the direct and indirect impact of ticks on cattle, combined with the cost of chemical treatment, was estimated at AUD $160 million in 2015.

Tick life cycles and life stages

Hard ticks have three life cycle stages: larvae hatch from eggs and have six legs; they shed their skin (moult) to become nymphs, which have eight legs; nymphs moult to become adults, which are male or female.

Males have a hard covering (scutum) over their backs; in females, the scutum covers only a small portion of the tick’s back, allowing the rest of the body to expand when she takes a blood meal.

The three stages each spend a number of days on a host taking a blood meal before they moult to the next stage. Fed and unfed stages differ markedly in size. Newly hatched larvae are very small and are often called ‘seed ticks’ because they look no larger than some grass seeds. When engorged, they are approximately pin-head size. Engorged nymphs are approximately match-head size, whilst engorged adult females vary in size according to species. Engorged female ticks on Australian livestock can be 10–15mm long.

The hard ticks are further distinguished by their life cycles into 1-, 2- or 3-host ticks. In Australia 1-host and 3-host ticks affect cattle.

One-host ticks

The cattle tick is a 1-host tick (Figure 1).

A larva finds a host and remains on it until it drops off as an engorged adult, approximately 21 days later. The moulting from larva to nymph and nymph to adult occurs on the one host. Each of the three stages lasts 5 to 7 days. Engorged female ticks drop off the host and lay their eggs on the ground (approximately 2,000 to 3,000 eggs in the case of the cattle tick) and these hatch to new larvae in approximately 3 weeks. The spent female tick dies. The cattle tick can therefore complete its life cycle, from newly laid egg to engorged adult, in approximately 6 weeks.

Depending on how successful the larvae are in finding the next host, cattle ticks can complete several life cycles in a year.

Three-host ticks

In a 3-host tick life cycle each stage engorges on blood from a different host for around 5 to 7 days then drops to the ground—the larvae and nymphs to moult, and the adult female ticks to lay their eggs and die. Each stage has to find a new host. This means that it can take as long as two years for a 3-host tick to complete its life cycle from egg to engorged adult (Figure 3).

Paralysis tick, bush tick, wallaby tick and bandicoot tick are 3-host ticks.

Signs of ticks and tick-borne diseases

Ticks are seldom seen on cattle, until the females are nearing engorgement, a day or two before they drop off. Large tick burdens, as can occur in the case of cattle tick, are seen more easily. Cattle that carry large numbers of ticks can be depressed, in poor body condition, and anaemic (pale mucous membranes).

Signs of tick fever and theileriosis (bovine anaemia) are often non-specific and can include depression, loss of appetite, weight loss, fever, anaemia, jaundice, abortion, recumbency (lying down and unable to rise), and death.

Cattle with Anaplasmosis (one of the causes of tick fever) can also become constipated. The passing of red urine (red water) is a sign of a number of disease conditions in cattle, including tick fever. These diagnoses need to be confirmed either with a stained thin blood film examined under the microscope, or from blood samples sent to the laboratory.

Tick paralysis starts with weakness in the hindquarters, which can lead to recumbency and death.