Classification of Medically I mportant Arthropods

Class Insecta Class Arachnida

Other Classes

Lice (blood) Fleas (blood) Bugs (blood) Flies (blood) –except 1

Mosquitoes (blood)

Head louse Pediculus humanus var. capitis pediculosis

Body louse Pediculus humanus var. corporis pediculosis, epidemic typhus (Rickettsia prowazekii), trench fever (Bartonella quintana), relapsing fever (Borrelia recurrentis).

Pubic/Crab louse Phthirus pubis pediculosis, sexually transmitted (pubic/perineal /eyelash/armpit hairs)

Bed bug Cimex lectularius Cimex hemipterus allergy, IIry bac. infection.

Reduviid bug (Family Reduviidae) Rhodnius, Triatoma (kissing bugs), Panstrongylus. American trypanosomiasis (Chagas' disease) (Trypanosoma cruzi). Transmission from Reduviid bugs: Reduviid bugs defecate while feeding → faeces contain trypanosoma → scratching → spread of faeces around site of bite → trypanosoma enter through site of bite.

Oriental/tropical rat flea Xenopsylla cheopis plague (Yersinia pestis), endemic typhus (Rickettsia typhi), host of Hymenolepis tapeworms

[H.nana–dwarf, H.diminuta–rat]. Northern rat flea Nosopsyllus fasciatus endemic typhus (Rickettsia typhi). Human flea Pulex irritans skin irritation - female fleas burrows into human skin for laying eggs, intermediate host of Hymenolepis & Dipylidium tapeworm larvae, ?plague. Transmission of Plague from fleas: flea is infected with Y.pestis → bacteria obstruct the oesophagus of the flea → when flea draw blood from rat/human → cannot swallow → regurgitate blood with Y.pestis

Sandfly –slender long legs, erected wings on resting Phlebotomus –old world sandfly Lutzomyia –new world sandfly leishmaniasis, bartonellosis, sandfly fever –a viral disease like flu. Black fly/Buffalo gnats humpbacked appearance

Simulium Onchocerciasis/river blindness (Onchocerca volvulus) –not in Sri Lanka. Tsetse fly Glossina African Trypanosomiasis (Sleeping sickness) (Trypanosoma brucei –T.b. rhodesiense, T.b. gambiense)

Domestic fly (non-blood) Musca domestica mechanical vector –transmits several viral Bacterial & parasitic diseases (swallow & regurgitate manner) –Ascariasis, Amoebiasis, myiasis.

Mosquitoes (blood)

Anopheline Culicine

Culex

Aedes aegypti urban vector man-made small collections of clear water (tires, tins, plastic/ glass containers, flower vases, blocked drains etc.) Aedes albopictus rural vector small collections of natural, clear water (tree stumps, leaves etc.)

Dengue (DF & DHF), Yellow fever, Chikungunya.

Culex quinquefasciatus polluted, stagnant water Lymphatic filariasis (Wuchereria bancrofti).

Culex gelidus husk pits Culex tritaeniorhynchus Culex fuscocephala paddy fields Japanese Encephalitis.

Aedes – dusk & dawn biters

Mansonia

Anopheles culicifacies clear, stagnant/ sluggishly moving water (drying river banks, gem pits, rock pools) rest at an angle to the resting surface. Malaria.

Class Arachnida

Mansonia spp. rural vector breeds on the undersurface of water plants (eg: Salvinia) Brugian filariasis (Brugia malayi)

Transmits Dirofilaria repens (a filarial nematode).

Ticks (blood) Mites Spiders & Scorpions

Other Classes Class Crustacea Cyclops Intermediate host of Guinea worm (Dracunculus medinensis)

& fish tape worm (Diphyllobothrium latum)

Fresh water crabs & Crayfishes Intermediate host of lung fluke (Paragonimus westermani)

Lobsters Shrimps

Class Myriapoda Centipedes non-fatal, painful swelling around site of “bite”.

mildly venomous local signs around bite wound rarely – severe reaction with extensive tissue necrosis

Soft Ticks (Family Argasidae) Argus spp. Allergic reactions; Tick paralysis –in animals & humans; Viral – Colorado tick fever, Crimean-Congo fever; Bacterial – Rocky mountain spotted fever, tick borne typhus, Q fever; Parasitic – Babesiosis. Hard Ticks (Family Ixodidae) Ixodes sp.. all disease under soft ticks, Lyme disease (Borrelia burgdorferi).

Chiggers/Red “bugs” Trombicula larva scrub typhus (Orientia tsutsugamushi), irritating dermatitis.

Itch mite Sarcoptes scabiei Scabies.

J.E. Filarial

House dust mite Dermatophagoides pteronyssinus (European house dust mite) Dermatophagoides farinae (American house dust mite) Euroglyphus maynei Asthma & allergic symptoms. their gut contains potent digestive enzymes (notably proteases) that persist in their feces and are major inducers of allergic reactions such as wheezing. their exoskeleton can also contribute to allergic reactions

Deer fly/Yellow fly Chrysops Loiasis (Loa loa), Tularaemia (Francisella tularensis).

2008 A/L Batch – Repeat Campaign (IPD Module)© MKGR (2012)

Important Diseases Caused By Arthropods

Disease Presentation TreatmentPrevention &

ControlPediculosis

Common in people of unclean habits & bathing is infrequent Eg: Inmates of jails,

mental hospitals, refugee camps, soldiers

Transmission Head louse – brushes,

combs, hats (most prevalent in school children)

Body louse – contact or clothing (through infested fomites)

Crab louse – during coitus (sexually transmitted), rarely through toilet seats, clothing or bedding

Symptoms are the result of cutaneous irritation & IIry infection.

Itching is the earliest & most prominent symptom.

Sequelae of scratching are the most characteristic signs: bite → irritating saliva

injected → inflammation →roseate elevated papules → severe itching → scratching → IIry bacterial infection → pustules & suppurative lesions

Severe infestation may produce following in the skin: Scarring Induration Pigmentation Ulceration

Infestation of eye lashes with IIry infection may lead to: Phlyctenular conjunctivitis Keratitis

Topical application of Malathion Pyrethroids Sulphur

(adequate time should be given after application – up to 8-12 hours)

Topical application of soothing lotions This relieve itching Thus prevent scratching & allow lesions to heal

Head lice Wash hair & dry it; apply shampoo containing 1%

ɣ-benzene hexachloride (ɣ - Cl6) (as directed in package insert) or

Topical application of 0.2% pyrethrin with 2% piperonyl butoxide (as directed in package insert) or

Topical application of 0.03% copper oleate (as directed in package insert)

Body lice Treat as for head lice Alternative: 1% malathion dust with 2nd option

above Crab lice

On pubic area, treat as for head lice For infestation on eyelashes

Remove nits & lice with forceps, or Topically apply Ophthalmic ointments of

Eserine (0.25% physostigmine).

Mass delousing programmes

Needed for institutions which are overcrowded

Topical application of insecticidal powders simultaneously to body & clothing Eg: 10% DDT, 10% ɣ - Cl6

People coming in contact with lice infested individuals in typhus epidemics may be protected by wearing silk or rubber outer garments fastened tightly at wrist, ankles & neck and by impregnating clothes with repellents.

Scabies Sarcoptes scabiei is the

only known species that causes human infection.

Female mite burrow into skin & lays eggs → larvae emerge from eggs & further burrow into skin (confined to corneous layer of skin)

Preferential sites are: Interdigital spaces Flexor surfaces of wrist Forearm Elbow & axilla Inguinal region &

genitalia Diagnosed by clinical

symptoms & demonstration of larvae from material taken from burrows & vesicles.

Clinical symptoms occur due to reactions against faecal matter & excreta of larvae.

Lesions with slightly elevated reddish tracts in the skin & minute vesicular swellings (esp. in individuals with fair skin)

Initially clinical manifestations may be mild, but after weeks when the skin becomes sensitized, it leads to:

Intense itching aggravated by warmth → scratching & spreading of infestation → IIry bacterial infection → multiple papular, vesicular & pustular lesions

Acute glomerulonephritis (secondary to Streptococcal skin infection) is described as a complication of skin lesions.

Bath with hot water & soap (hot-soapy bath) → application of topical scabicides → 2nd application is seldom necessary Benzyl benzoate cream (BB cream) Permethrin Malathion 1% ɣ - Cl6 ointment

Ideally the topical scabicide preparation should be applied to all areas of the skin (from neck to downwards)

For infants, children with large areas of denuded skin & pregnant woman:

10% Crotaminton or Pyrethrin with piperonyl

Treatment of infected individuals along with their entire family.

Sterilization of all clothing, towels & beddings.

Improve and maintenance of personal cleanliness

Prevent modes of transmission via; Close personal

contacts (family, over-crowded settings)

Fomites (beddings, clothing and towels)

Myiasis

Invasion of human tissues by larval stages of domestic/house flies (maggots)

May get into skin, wounds, urinary tract, intestine & rarely atria of the heart.

Clinical presentation depends on the tissue of invasion Wounds with worms

(maggots) GIT: vomiting, diarrhoea,

mature larvae may appear with stools.

UT: dysuria, haematuria, mature larvae may appear with urine.

Community measures to control density of flies (since flies travel considerable distances, it requires community measures to control).

Screening and trapping may protect the individual homes.

Elimination of breeding places by disposal or chemical treatment of animal excrement, garbage and other decaying vegetation.

Residual spraying of the interiors of the houses and barns with appropriate insecticides.

Hanging pyrethroid-coated fiberglass strips in barns.

2008 A/L Batch – Repeat Campaign (IPD Module) © MKGR

(2012)