Adult ticks and nymphs have four pairs of legs , a defined cephalothorax and abdomen ( not a separate thorax as in insects ) and no antennae . Ticks are dorsoventrally flattened ( compared with fleas , which are laterally flattened ). The scutum covers the whole dorsal surface in males but only part of the dorsal surface in females , making them sexually distinct . Genital pores are visible only in the adult stage and are placed between the second pair of legs . Ticks have forward-facing mouthparts , which include a hypostome with barbed teeth and chelicerae , both of which enter the skin . The salivary glands secrete a local anaesthetic which , along with the small , sharp chelicerae , allow the tick to bite without alerting the host . They will then ‘ cement ’ themselves to the skin to stay in place .
The length of the life cycle varies , depending on the area and species . Generally , in the UK , it takes a tick 2 – 3 years to grow from egg to adult . As an adult , the female will die after laying eggs , while the male can complete several matings over several days . In general , ticks spend a lot of their time resting and developing , with around 90 % of their life cycle spent in vegetation or a host ' s environment [ 1 ] .
Ticks will vary in the number of hosts they use . If they use one host , all feeds take place on one species of host ( e . g . cattle ), after which the female will drop off and lay eggs on the ground . The larvae and nymph of a two-host tick will feed on one host , and the nymph will drop off and reattach to another host as an adult . A three-host tick , such as Ixodes ricinus , will drop off and find a new host between every stage [ 2 ] . This is epidemiologically relevant because a one-host tick is easier to control , as all the life-cycle stages are on one host animal ( e . g . cows ). If the parasite is a twoor three-host tick , it will drop off and at subsequent stages will attach to other hosts . So , for example , the herd of cows can be treated , but there will still be other ticks on other hosts in the area , which will function as a reservoir . Treatment has a greater impact on a one-host tick than on a two- or three-host tick , because it will affect multiple life stages on the host and enhance tick control .
Ticks in northern Europe tend to search for a host in temperate conditions , when it is not too hot or windy . They will climb on to a leaf to wait for a host to brush past . Ticks may have a host preference in certain parts of their life cycle and a specific host for the adult stage . They may also have preferred feeding areas on a host [ 4 , 5 ] .
Figure 1 . Ixodes ricinus , commonly known as the sheep tick .
Life cycle and biology
The life cycle of Ixodes spp . begins when an engorged female is mated , falls off the host and lays her eggs in leaf litter . The female dies after laying around 2,000 waxy eggs . Hexapod larvae ( with three pairs of legs ) emerge and can survive for some time without feeding . When they find their host , often a mouse or rabbit , they feed for around 2 – 3 days . Once engorged , they drop off , digest their food and moult into an octopod nymph ( with four pairs of legs ).
It is often the nymph that will carry and transmit the disease , usually in spring when temperatures start to rise . The nymph feeds for around 4 – 8 days , drops off , moults and emerges as an adult . Male and female adults will find a host and , while the female is feeding / engorging , the male will mate with her . It is worth noting that Babesia canis can be passed on through the tick eggs , known as trans-ovarian transmission , so tick larvae can hatch already infected .
Ticks find hosts in a number of ways : vibrations , CO 2
, temperature , pheromones and odours , by using the Haller ' s organ on the end of the first pair of legs . Once on the host , they use their claws to hang on and move through the hair to find the skin . They may travel around the body to find specific or preferred areas , such as the axilla , ears or perianal area . They make little cuts in the skin , insert the hypostome and secrete ‘ cement ’ to keep themselves in place . This process takes time , making them easier to remove within the first 24 hours of contact with a host , which is why dog owners should be advised to check their animals as soon as they return from a walk . Once in place , they will feed . The tick may feed for up to 7 days . A 2 mg tick can take as much as 600 mg of blood .
Ticks utilise the proteinaceous material from cells in the blood but remove the fluid . Some of the fluid goes to the salivary glands and is injected back into the host . It is at this stage the protozoa can enter the host , as they reside in the salivary glands and enter at the same time as the saliva . In some diseases , such as Lyme disease , the transmission of bacteria does not usually happen for 24 hours . Therefore , if the tick is removed within this time , the risk of disease transmission is reduced .
50 Veterinary Nursing Journal