Lice on Humans

Announcements

1. Twitter account -- http://twitter.com/gcbrown147

2. Speaking today: Lindsey Henderson, Rachel Leneweaver

3. On deck for Tuesday: Lauren O’Mara; Subject: Plague

A major nuisance problem recently resurfaced

Watch the UK Video (Emmy Award Winner). It covers manyof the topics covered here in a very entertaining manner.

This video is 7 minutes long.To watch that video, click: HERE

Cimicidae

• Affects many vertebrates

• 23 genera, 91 spp.• Most common pest

of humans: Cimex lectularius

• All are dorsoventrally flattened

Bedbug in action video

Curious Biofact –Traumatic Insemination

Male pierces the female's abdomen with his penis and injects his sperm through the wound into her bloodstream. Female is permanently scarred by this.

In dense colonies, high female mortality results. Interspecific matings occasionally occur (e.g. C. lectularius X C. hemipterus) and are usually fatal to the female.

Bedbug history

• Common throughout European history• First pest control company formed in the

1600’s as a bedbug control service using tobacco.

• Introduced to N. America by colonists• Suddenly disappeared from most of the

developed world in the early 1950’s• Suddenly reappeared in the mid – late

1990’s

Reasons for Reappearance

• Use of long-residual insecticides declined• Increased movement of people & material• Increased used of specific pest controls

(e.g. baits).• Improved personal/environmental

measures?– Decrease in smoking– Decrease in toxic materials for furniture/carpet

manufacturing

Medical Significance

• No substantiated significant disease transmission

• Dermatological conditions/complications from bites

• Psychological/Psychiatric associated with long-term exposure (e.g. months)– Irritability from lack of sleep– Continued discomfort from bites– Financial/family stresses

Bed Bug Control

• Bed bug control is expensive, difficult, problematic, highly disruptive.

• Thorough vacuuming.• Bedding/furniture encasement or discard.• Heat treatment effective for fabrics.

Includes carpet steamers.• Insecticide treatments are generally the

last step (though may precede encasement).

Lice on Humans

• Order Phthiraptera means lacking wings• The only parasitic order of the exopterygotes (wings

develop outside the body, gradual metamorphosis).• Highly host-specific:

– live entire lives on one host individual; – cannot live off host; – opportunistic transmission.

• More than 3,000 known spp. but there are many more unknown. Biology/taxonomy of most species is poorly known.

• Note: Some things are called “lice” which are not. E.g. plant lice, louse fly.

• There are two basic kinds of lice: sucking & chewing (biting) but many believe that it’s more complicated.

Chewing Lice

Bird Hosts

Feed on skin, feathers

Mallophaga – includes 3 suborders (cf. Table 6.1 in text)

Many are poultry pests, some affect mammalian livestock as well.

Sucking Lice

Mostly Mammalian Hosts

Feed on blood/body fluids

Anoplura – No suborders, 8 families (cf. Table 6.1 in text)

All three human pests are in thing group.

Three Louse Species on Humans

• Body Lice (“cooties”), Pediculus humanus humanus L.– Cooties – from the Malay word, “kuti,” or

Polynesian word “kutu” meaning lice.– Body lice genetics show strong correlation

with human evolution. Read this.

• Head Lice, Pediculus humanus capitis L.• Pubic or Crab Lice, Pthiris pubis L. Note

the spelling of this Phthiraptera species

Human Lice – Body LouseLays most of its eggs on clothing, esp. seams.

Transmits all of the lice-borne pathogens.

Does not persist with frequent bathing.

Hardiest louse – can live off host for 3 – 4 days.

Infestation called Pediculosis corporis

Human Head Louse• Lays its eggs on hair (cf. pic)• Infestation often identified by eggs

– Appearance and susceptibility affected by hair color & race

• Resistant to bathing• Max survival time without host is 2

days• Infestation = Pediculosis capitis

Human Crab Louse

• Mostly found on hair in pubic region

• Can also be found in armpits, beards, eyebrows.

• Can only live a few hours off host

• Resists bathing.• Not a disease threat.

Health Threats from lice

• Three main pathogenic diseases:– Epidemic Typhus– Louse-Borne Relapsing Fever– Trench Fever

• These have had important impacts on human history but are now much less common.

• Book’s discussion on these is excellent.

Epidemic Typhus (ET)

• Rickettsial disease: Rickettsia prowazekii

• Very similar infection cycle as with Triatomines & T. cruzi

• Classic ET is the acute form. Chronic form is “Brill-Zinser” disease or recrudescent typhus.

• Non-human reservoirs can be the source of another form: “Sporadic ET”

Disease pathology

• Pathogen replicates mainly within vascular endothelial cells.

• Infected cells proliferate and degenerate, results in vascular occlusion.

• Occlusion induces a focal ulcer followed by hematogenous dissemination of the pathogen systemically.

• Abrupt onset of clinical disease after ~4 weeks: headache, fever, and often a hemorrhagic rash.

• Ocular lesions sometimes occur as with all of the diseases produced by Rickettsiae.

Louse-borne Relapsing Fever

• Spirochete bacterium, Borrelia recurrentis

• Pathogen infects the louse blood stream, is transmitted when the louse is crushed & rubbed in to the skin.

• Few thousand/year, 95% of cases are in Ethiopia.

Trench Fever

• Bacterial disease, Bartonella quintana• A form of “Bartonellosis”. We’ll see

another one later.• Like typhus, transmitted in louse feces.• Often asymptomatic in healthy hosts. May

express nonspecifically in stressed hosts.• Increased association of stress & urban

environments leads to term: “Urban Trench Fever”.