Arthropod Vectors and Vector-Borne Disease

How many hosts (and rounds of feeding) per tick lifecycle?

3

Louping ill - incubation period

6-18 days

Trans-ovarial transmission

Adults female infected and pathogen passed on to eggs (between generations)

Tick lifecycle

Adults lay eggs - forms egg clutch. Hatch into larvae. Larvae have six legs. Feed on host, digest blood meal. Become 8-legged nymph. Attaches to new host. Feeds for 7-8 days, engorges, drops off host. Digests blood. Moults to become 8-legged adult. Adult attaches to new host (3rd host). Blood meal, engorge, drop off, digest blood. Lay eggs. Adult dies.

Arthropod vectors

Blood feeding - transmit pathogens (bacteria, viruses, protozoa, helminths)

Diagnosis of louping ill

Blood test Detecting virus in brain tissue Microscopic lesions

Ceratopogonidae (biting midges) transmit

Blue-tongue African horse sickness

Pathogen causing lyme disease + vector

Borrelia spp. Ixodes ricinus

Tick pyaemia - clinical signs

Debility, crippling lameness, and paralysis. Pyaemic abscesses in joints/organs

Fleas transmit

Dipylidium caninum Rickettsia felis Yersinia Bartonella

Drugs active against ticks

Imidacloprid Fipronil Pyrethrins and pyrethroids Amitraz Fluralaner Afoxolaner

Advantages of plunge dips

Immediate and effective treatment. Protects against sheep scab, blowfly strike, lice and keds.

Most common tick in UK of companion and livestock animals

Ixodes ricinus

Tick pyaemia - animals affected

Lambs 2-12 weeks old

Trans-stadial transmission

Larva infected and pathogen passed on between lifecycle stages (larva to adult).

Psychodidae (sandflies) transmit

Leishmania spp

Advantages of pour-on treatments

Longer protection and easier to administer

Characteristics of a biological vector

Lots of things between host/vector interact to determine risk of infection. - vector survival rate - pre-patent period (when pathogen going through lifecycle within vector) - period of infectiousness - Biting rate/meal size - Vector/host density - Distribution of infection Vector must live longer than prepatent period.

Relationship between small mammals and ticks

Main host for tick larvae. Reservoir hosts as the infection circulates in the small mammal population. From the reservoir population, pathogens acquired by larvae are transmitted transtadially to nymphs and adults which infect other hosts.

Culicidae (mosquitos) transmit

Malaria Dengue fever Yellow fever Encephalitis Filariasis Dog heartworm

Disadvantages of pour-on treatments

No immediate tick kill

Do all ticks engorge?

No, only female

How does the height of questing behaviour affect the tick's lifecycle?

Older the tick, the higher they climb before dropping off to absorb more water from damp environment. Height climbed influences type of host that tick is likely to encounter. E.g., larvae - 0.2m - rabbit Adult - 0.8m - deer

Simuliidae (black flies) transmit

Onchocerca volvulus

Why are ticks difficult to control?

Only 2% of lifecycle spent on the host = short opportunity to attack. The timing of peak activity is weather dependent and can be hard to predict.

Disadvantages of plunge dips

Operator safety Environmental toxicity Legal controls on use and disposal

Tick treatments in livestock

Plunge dips (diazinon) Pour-on (deltamethrin, alpha-cypermethrin, cypermethrin)

Why is it a good idea to inspect dogs for ticks regularly?

Regular inspection and early tick removal is important - takes time for pathogen transmission to occur... o Borrelia - at least 24 h o Babesia - at least 48h possibly several days

Deer in Lyme Borrelia lifecycle

Reproductive hosts Dead-end hosts Dilution hosts

Why can disease transmission not always be excluded when using tick treatments like Bravecto and Nexgard spectra?

Requires ticks to feed on the host for drug to work therefore possible to transmit disease.

Most common tick in the world (except UK)

Rhipicephalus sanguineus (brown dog tick)

Which anti-tick product repels ticks from feeding for the longest time in dogs and cats?

Seresto collar - repels ticks from feeding for up to 8 months

Pathogen causing pyaemia in lambs + vector

Staphylococcus aureus Ixodes ricinus

Lice transmit

Swine pox fever Bovine anaplasmosis

Risk factors associated with tick-borne disease

Warmer climate Changes in leisure activities - more walking, hiking, etc. Increasing population of hosts Host species encroaching urban areas Travelling pets

Why are deer sometimes "dilution" hosts?

When deer are not competent hosts for the pathogen, they divert ticks away from competent hosts and effectively remove circulating pathogens from the system. Ticks bite deer but do not increase the rate of transmission, only increase the population of ticks.

Relationship between deer and ticks

Wild deer = reproductive host for adult ticks. Adults reproduce after feeding on deer. Deer abundance and tick abundance strongly correlated.

Anaplasmosis - clinical signs

· Sustained high temperature, anorexia, and depression. · Suppresses the animal's immune system predisposing it to further diseases. · Lambs - louping ill, tick pyaemia and respiratory disease. · Naive pregnant sheep likely to abort and may develop severe metritis (inflammation of the uterus) if untreated. · Naïve rams may be infertile for up to one month after infection. · Cattle (pasture fever) and deer rarely show clinical signs of disease but may act as reservoirs of infection.

Direct effects of tick feeding

· blood loss, anaemia · inflammation, · bacterial infection · restlessness, poor feeding · reduced body condition and lower productivity. · tick paralysis

Saliva-assisted transmission (SAT)

Transmission at co-feeding

Why are deer sometimes "dead-end" hosts?

in the case of pathogens like Lyme Borrelia, deer are not competent hosts, they do not transmit infection - so deer are described as dead-end hosts.

Biological vectors

pathogen must go through stage of lifecycle in vector. Can regurgitate pathogens in saliva, blood, or faeces

Mechanical vector

pathogen on external surfaces and mechanically transmitted = less efficient

Prevention of redwater fever (babesiosis)

· Identification of risk areas · Prophylactic treatment of cattle about to be moved to a risk area · Tick control · Vaccine not yet available in UK

Redwater fever (babesiosis) - clinical signs

· Increased temperature · Diarrhoea which ceases after around 36 hours and then becomes constipation · Red urine (due to haemoglobin produced by the rupture of the red blood cells) which becomes darker with time. · Tachycardia · Abortion · Death is rare

Characteristics of a mechanical vector

· Interrupted feeds - i.e., if bite painful and host reacts. · Short re-feeding interval · High fly mobility - move quickly from host to host to transfer pathogens. · High survival of pathogens on insect · Less important in terms of transmitting disease compared to biological vectors.

Tick pyaemia - pathology

· Staphylococcus aureus is the main cause of the pyemic abscesses. · Bacteria enter bloodstream either by direct inoculation during tick feeding or from local superficial wounds.

Louping ill - clinical signs

- fever, depression, inappetence. - Acute phase: muscular trembling, unsteady or high stepping gait - Seizures and paralysis - coma and death

Pathogen causing babesiosis in cattle + vector

Babesia divergens Ixodes ricinus

Predisposition to tick pyaemia

Anaplasma infection High risk areas for Ixodes ricinus

Pathogen causing anaplasmosis + vector

Anaplasma phagocytophilum Ixodes ricinus "Tickborne fever"

Tick borne disease of livestock in Europe

Anaplasmosis Louping-ill Babesiosis (red water) Pyaemia

Tick-borne disease of dogs and cats in europe

Anaplasmosis Lyme disease (dogs) Babesiosis Ehrlichiosis Hepatozoonosis

Which arthropod group carries the widest range of pathogens?

Ticks

Questing behaviour

climb up vegetation and sit, wave legs around (tasting air), grab hold of hosts