Mites and Humans Chapter 25

AnnouncementsAbout the test …Speaking today: Carolina EscomillaSpeaking Thursday: Morgan BiggerstaffNext Tuesday: April NipperGuest Lecture Thursday: Dr. Lee TownsendRead Chapter 26 for Thursday: TicksRead Chapter 24 for next Tuesda: Spiders

Mites

• Class Arachnida, Subclass Acari• This subclass includes the ticks (next lecture). Note:

There is a discrepancy in the taxonomy of ticks between Chaps 25 & 26. We will follow that of Chap 26.

• This lecture discusses the non-tick groups of the Acari• One of the most common but least recognized sources

of arthropod-borne human suffering in the US.• Very large group. Includes many plant pests, beneficial

species, and external parasites of other arthropods.• An important characteristic of the group is the ability to

rapidly develop resistance to chemical insecticides.• Although small, they can typically endure extremely

adverse environments. This is why they sometimes create acariasis.

Mite Morphology

• Most have piercing/sucking mouthparts, some have chewing mouthparts. All are different from insects

• Most are 8-legged except for the 1st instar which is 6-legged.

• All are extremely tiny. A big one is the size of a period in your textbook. Some adults live inside hair follicles. Some live inside trachea of insects.

Identification

• Only a few specialists are adept at it.

• Based on external morphology– setal pattern– mouthparts– reproductive organs

Mites of Medical Importance

• Acariasis - rare

• Allergies – extremely common

• Dermatitis

• Skin-Invading Mites (follicle, Sarcoptes)

• Disease Transmission

• Psychological Disorders

Allergies & House Dust Mites

House Dust Mites

• Extremely common & prolific• Body fragments & fecal material are allergens• Many products/services available allergy control• Many of these promote claims that have become

urban legends:– Pillow weight & HDM– Feather pillows are worse than synthetic – opposite is

true– Many more myths here

Chiggers & Dermatitis• Mites in the family trombiculidae• Pierce skin, suck fluid• Only the 1st instar larvae feed on humans,

other stadia are predators• In our area, most common in late

spring/early summer.• Especially common near flower beds

Skin-Invading Follicle Mites

• Demodex spp. mites.• Host specific – most common

human species are D. folliculorum & D. brevis

• Lives in pores of hair follicles, esp. on the face & esp in eyelashes

• Incidence increases with age

Skin-Invading Sarcoptes

• Sarcoptes scabiei is the human scabies mite.

• Also cause mange in many animals.

• Clinical forms of scabies:– Papular– Bullous– Nodular– Crusted

Papular Scabies – most common

Pruritic rash means an itching rash.

Bullous Scabies

Nodular Scabies

Norwegian or Crusted Scabies

Mange is a bigger Vet problem

• Demodectic Mange (Red Mange)– Caused by follicle mites– Host loses control because

of another problem– Not normally contagious

• Sarcoptic Mange– Caused by Sarcoptes

mites– Highly contagious

Demodectic

Sarcoptic

Pathogens Transmitted by Mites

• Rickettsialpox– Transmitted by house mouse mite– A spotted fever rickettsia

• Papule dries, becomes scab (eschar)• Generic systemic symptoms

• Scrub Typhus (Tsutsugamushi)– Transmitted by various chigger spp. – Different spp. have different

seasonal/geographic distributions.– Chiggers themselves are reservoirs.

Rickettsialpox eschar

Scrub Typhus primarily a problem in Asia & Pacific Islands (inc. Aust.)

Fly Management Continued

Spinosyns for Diptera Control

• Different mode of action from other nerve poisons (mostly used on adults)

• Wide use in agriculture• Can be used in rotation with other

larvicides• Classified as “Reduced Risk”• Active area of work with new

applications still being found.– e.g. promotion of wound healing.

Larvicides:Insect Growth Regulators

• Methoprene is the most common.

• Advantages – Harmless to non-insects, inexpensive, rapid acting

• Disadvantage – no additional effect on adults, affects other insects (including beneficials)

• Examples• PreStrike Granules

• Methoprene is the most common.

• Advantages – Harmless to non-insects, inexpensive, rapid acting

• Disadvantage – no additional effect on adults, affects other insects (including beneficials)

• Examples• PreStrike Granules

Larvicides: Microbial AgentsBacillus sphaericus & Bacillus thuringiensis israelensis (Bti)Bacillus sphaericus & Bacillus thuringiensis israelensis (Bti)

• Advantages– Non-target Safety– Control for 30+ days

• Disadvantages– Short window of treatment

opportunity– May have disagreeable

odor/appearance

• Examples

– Mosquito Dunks

– Mosquito Quick Kill Granules

– VectoLex

• Advantages– Non-target Safety– Control for 30+ days

• Disadvantages– Short window of treatment

opportunity– May have disagreeable

odor/appearance

• Examples

– Mosquito Dunks

– Mosquito Quick Kill Granules

– VectoLex

Larvicides: Physical Smothering Agents

“Suffocates” mosquito• Advantage:

– Also acts on pupae and ovipositing adults

– Can be used to treat very large areas

• Disadvantage:– Oil film– Subsurface larvae

• Examples:– BVA, Golden Bear– Agnique (monomolecular)

Adult Fly Management

• Personal Protection

• Exclusion (buildings, small areas)

• Insecticides– Residual– Non-residual

• Other– Trapping in sensitive areas– Mating Disruption

Personal Protection

• Stay indoors at dusk & during evening hours

• Long shirts and pants• Repellants

– Deet: • N,N-diethyl-metatoluamide• 30%

– Non-deet: • Eucalyptus oil • Avon Skin-So-Soft• Citronella oil

Repellents – Two TypesPersonal Small Space

Protects a single individual

Effective Range ~ 1 foot

Protects a small group of people

Effective Range ~ 10 feet

Mechanical Exclusion

• Shut them out

• Netting and Screening– 16-18 mesh

Adulticides

• Nonresidual Area Sprays– Contact insecticides, droplets must make

direct contact with mosquito

• Dominant Products– Sumethrin + PBO (Anvil)– Resmethrin (Scourge)

Non-residual adulticiding is used for large-area space treatments using

ULV equipment• ULV = “Ultra Low Volume”

– Very small droplets;8 to 30 microns

• Prefer low air currents:– 3.2 kph to 12.9 kph– Excessive wind & updrafts

reduce control but some is necessary for dispersal

• Disadvantages: – Gets everywhere: in

residences, on food, etc.– Expensive– Products may act by temporary

repellency

Perimeter treatments use residual pyrethroids

• “Pyrethroids” synthetic derivatives of chrysanthemum extracts•Advantages

•Provides weeks of control• Residual but do not move in the food chain

• Disadvantages• Extensive non-target arthropod effects• Fairly expensive