Ticks

Question 1

Tick morphology and characteristics

Answer 1

Larva, nymph and adult stages feed on blood and look very similar (hemimetabolous)

Toothed mouthpart (hypos tome)

very small larvae (<2 mm) but large adults (0.5-2.5cm)

long lived (months-years)

resistant to environmental stresses and can survive long periods of time without hosts and feeding

high reproductive potential (<15,000 eggs per female)

Question 2

How can ticks be classified

Answer 2

Soft - Argasidae

Hard - Ixodidae

Question 3

Differences between hard and soft ticks

Answer 3

Hard ticks spend a long time on the host and drop off into vegetation

soft ticks spend a short time on the host and drop off into the home

mouthparts/gnathosoma/capitulm of hard ticks visible and hidden in soft ticks

hard ticks have a scutum/shield but soft ticks do not

Question 4

life cycle of hard ticks

Answer 4

egg, larva, nymph, adult

each stage feeds only once

attach to host for days (larva and nymph) or weeks (adults –> adult female feeds once, drops off the host, lays 1000s of eggs and dies

1000s of larvae quest on the tips of vegetation and await hosts

large adults less common on humans than larvae or nymph

rest in cooler shaded vegetation to moult and wait for hosts

Question 5

types of hard tick

Answer 5

one-host ticks - all stages on 1 individual (Boophilus)

two host ticks - larva, nymph on 1, adult on second individual (Hyalomma)

three host ticks - each stage on a different individual (Ixodes, Dermacentor, Rhipicephalus, Haemaphysalis)

Question 6

Features of hard ticks

Answer 6

chelicera
hypostome
palp

Question 7

why do hard ticks have high vector potential

Answer 7

Firmly attached and persistent blood feeders
trans-ovarial transmission (passed to offspring)
trans-stadial transmission (passed between egg-larval-nymph-adult)
ticks are both reservoir and vector
they are long lived
slow feeding aids in dispersal while attached
wide host range in many spp

Question 8

Why are hard ticks important in humans

Answer 8

vectors to humans for arboviruses, rickettsias, spirochetes, other bacteria

tick paralysis

Question 9

Human disease transmission by hard ticks

Answer 9

Tick borne encephalitis 
Omsk haemorrhagic fever 
Kyasanur forest disease 
Crimean congo haemorrhagic fever
Colorado tick fever 
Rocky Mountain spotted fever 
Mediterranean spotted fever 
African tick bite fever 
Q fever 
Human ehrlichiosis
Lyme disease 
Tularaemia 
Tick paralysis

Question 10

Kyasanur forest disease

Answer 10

400-500 human cases per year

Haemaphysalis ticks In Southern India - 3 host

larvae on birds in forest and nymphs on small mammals and monkeys

foresters, herders and their cattle pick up adult ticks

trans-stadial transmission of virus in tick but also amplification within monkeys in the forest - monkey deaths are sentinel to human outbreaks

agric development and deforestation results in a decrease in disease and disease is spreading out of the Kyasanur forest

vaccine exists for KFD

Question 11

Tick paralysis

Answer 11

Hard ticks only as they are attached for a long time

Toxin in saliva pumped continually during feeding

5-7 days after tick attaches - ascending paralysis, speech, swallowing, breathing difficulties, respiratory failure and death

easily confused with poliomyelitis

younger children most effected

removal of ticks results in quick recovery

Question 12

Control of hard ticks

Answer 12

Treatment of livestock and pets with any range of insecticides applied by dipping or ear tags

ivermectin at 4 week intervals

personal protection

treatment of infested areas - UL V suitable

Question 13

Soft ticks (Argasidae) of importance

Answer 13

Ornithodoros sp

Painful bites, sometimes in large numbers within houses

Vector of tick borne relapsing fever in humans

Vector of African swine fever virus (pigs)

Question 14

Soft ticks life cycle

Answer 14

eggs, larvae, nymph 1, 2, 3, 4, adult

Question 15

tick borne relapsing fever

Answer 15

only very important soft tick transmitted human disease

various Borrelia sp. transmitted by various Ornithodoros sp in most of the tropics and subtropics –> most important in Africa

East Africa - Borrelia duttonii and Ornithodoros moubata - no non human reservoirs

West Africa - Borrelia crocidurae - zoonotic and humans occasional

Question 16

What species cause tick borne relapsing fever in East Africa

Answer 16

Borrelia duttonii

Ornithodoros moubata

Question 17

What species causes tick borne relapsing fever in West Africa

Answer 17

Borrelia crocidurae

Question 18

How is tick borne relapsing fever transmitted

Answer 18

Spirochetes enter the tick haemocoele, multiply, then enter the salivary glands, the coxal organs and the ovaries (~3days)

transmitted through the saliva and coxal fluid but not in the faeces

Trans ovarial and trans stadial transmission of B. duttonii (tick reservoir for <10 generations)

Question 19

Symptoms of tick borne relapsing fever

Answer 19

High fever
Head, muscle and joint aches

recurring fever, roughly 3 days on and 7 days off

febrile episode ends with a ‘crisis’ - very high fever of up to 41.5 C for 10 to 30 mins

flush phase - sweats and rapid drop in body temperature

patients who are not treated will experience several episodes of fever before illness resolves

Question 20

Lab tests for tick borne relapsing fever

Answer 20

Unlike other spirochetes, TBRF ca. reach high levels in blood during the febrile phase which can be detected by microscopy

Question 21

Treatment of tick borne relapsing fever

Answer 21

Tetracycline - 500mg/ 6 hourly/ 10 days

Erythromycin when tetracyclines are contraindicated

Neuronal complications - ceftriaxone 2g/day for 14 days

Question 22

Control of soft ticks

Answer 22

Sweeping floors

Improved housing with solid floors

Improved beds - raised off the floor will prevent tick biting

repellants

insecticide treated bednets