Ectoparasites 1 (Dr Smith) ATM and Intro Flashcards
What are the generic signs and symptoms of an ectoparasite infestation?
Itching, scratching, bites, soreness Generally not life threatening Infestation not infection Mild to servere discomfort, secondary itching from scratching Social stigma
What ectoparasites come under the Anthropoda phylum?
Ticks, mites, fleas and lice
What Class are ticks and mites?
Arachnida
What Class are fleas and lice?
Insecta
What are fleas and lice?
Insecta
6 legs, wingless
What are ticks and mites
Arachnida
8 legs, spiders/scorpions
What do Insecta and Arachnida have in common?
All blood-sucking parasites
Ectoparasites (live on skin)
Tend to be host specific
What is the lifecycle of a tick?
Three hosts
- Adults females drop off host to lay eggs
- Eggs hatch into 6 legged larvae
- Larvae attach to and feed on the first host (squirrel)
- Larvae detach from the host and molt into nymphs
- Nymphs attach to secondary host (rabbit)
- Nymphs molt into adults after leaving second host
- Adults attach to the third host in the spring for feeding and mating
What is the latin name for Ticks?
Ixodes ricinus
What is questing in ticks?
‘Questing’ is when ticks climb tall grass / shrubs and attach to a passing host, playing in long grass or hiking
Inspect skin at the end of the day (check especially in warm sweaty places)
What are the signs associated with tick infestation?
Move up body Exposed limbs (tops of legs and arms) Neck Do not itch Visual examination only way to detect
How are ticks treated?
No pharmacological treatment
Physical removal; use tweezers, do not squeeze or crush body, do not leave head behind
Do not try to burn off or other noxious means
Keep tick for positive identification
What are the two possible consequences of ticks (if undetected or incorrectly removed?)
Tick-borne encephalitis
Lymes disease
What is Tick-Borne Encephalitis?
A viral disease caused by ticks
-Flavivirus
-Infect the brain
Symptoms –> seek immediate medical help
What is Lymes Disease?
Bacterial disease carried by tick
-Spirochetes can be released if the head or body is crushed/left undetected
What are the symptoms of Lymes Disease?
Bulls eye rash
Flu like symptoms
Tired and general malaise
Incubation 2-100 days
What two types of mites are there?
Bed mites and scabies
What are the signs and symptoms of bed mites?
Itchy bites
- allergic reaction
- bites in straight lines; not random like in mosquitoes or flies
What is the treatment for bed mites?
Minimal; symptomatic treatment
-empirical treatment for bite reactions such as antibiotics, antihistamine, topical or oral corticosteroids
Prevention; general hygiene, hot washes 60 and airing bed clothes
What is the latin name for bed bugs?
Cimex lectularis
What is the latin name for scabies?
Sarcoptes scabiei
What are the signs and symptoms of scabies?
Epidermal skin infestation
Feed in tissue and fluids
Characterised by superficial burrows and pruritis (intense itching)
Like skin folds; fingers, buttock and breast creases
Visual signs: Ensure not impetigo or eczema; burrow marks and ink tests
Skin biopsy - scabies mites
What causes pruritus in scabies infestation?
IV-sensitivity reaction to mite, saliva, eggs or excrement
What is SMIPP? What is the consequence of it?
Scabies Mite Inactivated Protease Paralogue
Protein with no enzyme activity
Antagonist to PAR-2 on keratinocyte
Inhibit inflammatory response: aid infection by the mite
How are scabies contagious / transmitted?
Scratching, picking up the mites under fingernails or touching infected persons skin
Fomites; keyboards, toilets, clothing, towels, bedding, furniture
Survive for up to 14 days away from host
Symptoms develop after 3-4 weeks
Who are most at risk from scabies infection?
Elderly people, children, young mothers from infested children, sexually active people (STI)
How long are people infected with scabies?
Indefinite life cycles within host
Who else needs Tx once a person is found to have scabies?
Family and partner(s)
How can scabies be treated?
Insecticides; acaricides Permethrin cream Malathion lotion Ivermectin Benzyl benzoate
What is the 1st line treatment of scabies?
1st line is Permethrin cream 5% (Lyclear)
More effective than topical crotamiton 10% or oral ivermectin
2nd line is Malathion Lotion 0.5%
Itching treated with crotamiton (Eurax) and sedating antihistamine
What class of drug is Permethrin?
A synthetic pyrethoid Similar to the natural pyrethrins from Chrysanthenum An ion channel agonist Acts on nervous system of animals It is a neurological toxin
How does Permethrin act as a neurological toxin?
Binds to Na+ channels in animals and prolongs Na+ activation
This paralyses animal function and leads to death
How does Permethrin not cause neurological toxicity to human cell Na+ channels?
Arachnida have a different activation gate to human channels
Insects are more susceptible because of the sequence of domain II S4-S5 linker at the kdr sire (M918)
How are mutations notated in resistance diagrams for pyrethoids?
M918V
Methionine has mutated to V-something at the position 918
When is Permethrin 5% cream (Lyclear) contraindicated?
Absorption of topical cream is minimal; so there is no risk for breastfeeding but cream shouldn’t be applied to the nipple.
What are the counselling points for Permethrin 5% cream?
Itching may persist up to 3 weeks post treatment as animal material and faeces remain under skin
Suspect treatment failure if;
after 6 weeks if itching persists
new burrows appear
Treatment non-compliance - Tx over night; complete coverage and then repeat one week later
Treat personal, close contacts to avoid reinfestation
Drug resistance; if suspected, biopsy needed to genotype animal for drug resistance and then Malathion 0.05% lotion may be needed
What class of drug is Malathion?
Acetylcholinesterase (an organophosphorous compound)
It is a neurological toxin and binds irreversibly to cholinesterase (so that it cannot metabolise/remove the Ach) and promotes all cholinergic neurotransmission. This leads to post-ganglion excitation that leads to continuous muscle excitation and contraction. (Paralysis)
Is Malathion toxic to humans?
Low toxicity - only with long exposure/overdose can it cause problems.
Ingestion and metabolism of the lotion to malaoxon is far more toxic; chlorination of water promotes oxidation to malaoxon.
The malaoxon acts as an anti-cholinesterase in man; over excitation of Ach receptors
Where does ACh act on muscarinic receptors?
What associated side effects can be expected in Malaoxon poisoning?
Sweat glands, salivary glands and adrenal medulla
Side Effects: Miosis Salivation Sweating Bradychardia
Where does ACh act on nicotinic receptors?
What associated side effects can be expected in Malaoxon poisoning?
Skeletal muscle (somatic efferent system)
Fasciculation (twitching of SkM)
Paralysis - depolarising neuromuscular block
Ach also works on central nervous system by releasing NA.
What associated side effects can be expected in Malaoxon poisoning?
Anxiety, restlessness and dizziness
What class of drug is Ivermectin?
Macrolytic lactone
Derived from Streptomyces bacterium; an example of an ion channel agonist that acts on nervous system of animals
How does Ivermectin work?
It is a neurological toxin that binds and activates GluCl (glutamate gated chloride channels) by mimicking glutamate.
GluCl channels are a member of the Cys-loop ligan gated ion channel variety and are invertebrate specific. Ivermectin causes persistent opening and parylses animal function.
What are the counseling points of Ivermectin?
Oral administration
Does not cross the BBB (and no glutamate receptors in the brain anyway so safe for humans), P-glycoprotein efflux
Not given to children <5 y/o, in breastfeeding women or in renal/hepatic diseases.
What are the potential complications of scabies?
Secondary infection: Stapylococcus or impetigo due to scratching. Treat with antibiotics
Social stigma
Crusted scabies: in extreme infestations (thousands to millions) - does not itch, thick, warty crusts form, immuni deficient patients are more vulnerable. Treat with Ivermectin 200mcg/kg by mouth.
How can scabies be prevented?
Avoid sharing clothes, bed linen or towels
Dirty hotels and accomodation avoided
General hygiene
