Ticks
Order: IXODIDA
Family:
Ixodidae(hard)
Argasidae(soft)
Description
The hard ticks- Ixodidae- have a highly patterned scutellum covering some, or all of the back. They have forward projecting mouthparts which are visible from above.
The soft ticks - Argasidae- do not have scutellums and are soft and wrinkled in appearance. The mouthparts are not visible from above.
Habitat
Ticks are found amongst foliage and grasses, either holding on to the tops waiting for a suitable host, or down amongst the crowns. They are also found on a wide variety of hosts from dogs to humans.
Life-cycle
Once the female tick has taken a blood meal she falls off the host and drops to the ground. The female will lay her eggs several weeks later in the roots of grass and amongst vegetable debris. Once she has laid her eggs the female tick dies.
The newly hatched larvae have six legs instead of the eight which adult ticks possess. The young larvae climb up the foliage to seek a suitable host, they rest on the grasses holding on with their hind legs whilst stretching out their other limbs. Once they have found a host they select a suitable feeding area and embed their mouthparts into the skin, where they remain feeding for 3 - 4 days until they are full engorged. They then drop to the ground and find somewhere safe to moult to the next eight legged nymphal stage, called an octopod nymph. This is host seeking process is then repeated once more so that the octopod can moult to an adult. The blood meal is taken over a longer period of time, some 4 - 8 days.
The adults repeat the host finding process but the female does not feed until she has mated, then she will feed for 8 - 9 days before dropping off the host and seeking a suitable hiding place in which to lay her eggs. The males do not feed to engorgement only feeding for a few hours at a time.
If a suitable blood host is not found the tick is able to survive prolonged periods of time without food by remaining in humid areas where they can take water from the atmosphere.
Transmission
Tick-borne paralysis
- Only disease caused directly by ticks
- Tick injects narcotic saliva containing neurotoxin into host
- Associated mainly with hard ticks
- Amblyomma, Dermacentor (in N. America )
- Ixodes (in Australia & South Africa )
- Symptoms: fatigue, numbness in lower legs, muscular pain
- Death can occur due to respiratory failure
Lyme Disease
- Caused by a spirochaete, Borrelia burgdorferi, in Ixodes spp.
- Acquired by the larval nymph from field mice as it feeds.
- Transmitted to humans by the nymph.
- Symptoms: an enlarging annular skin lesion - erythema chronicum migrans (ECM) - and arthritis
- Later symptoms include involvement of the CNS
Rocky Mountain Spotted Fever (RMSF)
- A tick-borne typhus caused by Rickettsia rickettsii
- Transmitted by Dermacentor, Amblyomma, Ixodes, and Ornithodoros.
- No eschar at bite site
- Abrupt onset of fever after 6-10 days with severe headaches, muscle pains and a dry cough
- 2-3 days later, typhus rash of fine pink macules develops soles of the feet, wrists and forearms
- Similar disease caused by Rickettsia conorii and transmitted by Rhipicephalus sanguineus in the Mediterranean is known as Boutonneuse Fever (less severe than RSMF)
Colorado Tick Fever
- Virus carried by Dermacentor andersoni
- Confined to Rocky Mountain States of USA and Canada
- Symptoms: Similar to RSMF but less severe - very rarely fatal
Q Fever
- Caused by Coxiella burnetii
- Transmitted by Ornithodoros , Amblyomma and Rhipicephalus to livestock
- Transmission to humans is via domestic animals
- Symptoms: Initially resembles typhus without the rash
- Can lead to hepatitis, pnuemonitis & pericarditis
Relapsing Fever
- Caused by Borrelia spp. (spirochaete) transmitted by Ornithodoros spp.
- Transmitted via saliva and also coxal fluid from the tick
- Incubation period: 2-14 days; initial attack: 4-5 days
- Symptoms: Headache and fever, sometimes diarrhoea, bronchitis and pneumonia
- Usually 3-6 relapses, but 11 have been recorded
- Mortality is less than 10%
Babesiosis
- Caused by a protozoan, Babesia microti and transmitted by Ixodes spp. Non-specific symptoms: fatigue, fever, myalgia, sweating
Case study Lyme’s Disease
Lyme disease is the most serious arthropod-borne human disease of Europe and North America . In 1990 approximately 8000 case were reported. In the UK approximately 200 cases occur each year.
It is caused the bacteria / spirochaete/ Borrelia burgdorferi
- Phase 1 A few days after the bite a characteristic rash spreads out from the site of the bite, this lasts for 4 weeks + and is accompanied by flu like symptoms. In the UK bites are most frequent during July.
- Phase 2 After this period the bacteria can invade the body causing facial paralysis, muscular pain, spinal cord dysfunction, with symptoms like multiple sclerosis, and meningitis may also arise.
- Phase 3 Some patients, months or years later go on to develop a third phase which can cause serious fatigue and arthritis.
Lyme Disease Treatment
Effective treatment is possible with penicillin, tetracycline or cephalosporins.
Transmission
If the tick is removed in a clumsy fashion the mouth parts especially the hypostome will be left in the bite puncture, this increases the chance of secondary infection.
The best method for tick removal is:
- Place some surgical spirit on the tick.
- Then hold the tick firmly with a pair of forceps.
- Push the tick's body towards the hosts tissue and twist; this will release the barbed hypostome.
- Then pull the tick away.
Alternatively the tick may be removed by irritating it, this can be done by:
- Burning it with a cigarette or a red hot needle.
- Covering it with liquid paraffin, or Vaseline (thus preventing it from breathing).
