Arthropods Of Medical Importance (2/2)

Subphylum Crustacea Subphylum Uniramia Subphylum Chelicerata

Arthropods: Acari Ticks and Mites Phylum Arthropoda

Subphylum Chelicerata Large, diverse group of arthropods Includes horseshoe crabs, spiders, sea spiders, scorpions Most have 4 pairs of legs Some mites have one to three pairs External segmentation reduced Two body parts Capitulum (gnathosoma) Contains the mouthparts Idiosoma Legs and tail Most are free-living, non-parasitic Ticks and mites are parasitic Class Arachnidae Subclass Acari Order Ixodida Order Mesostigmata Order Prostigmata Order Oribatida Order Astigmata Order Ixodida Ticks Hard ticks Soft Ticks Four life cycle stages: egg, larva, nymph, adult May have one to six nymphal instars In many species, all stages are solenophagous ectoparasites In some, all instars are on one animal. In others, each instar finds a new host Increases transmission of disease Some are host specific, some are opportunistic Can live as long as 16 years without blood meal! Life span may be as long 21 years Very complex behavior Controlled by pheromones Family Ixodidae Hard Ticks Capitulum is terminal and can be seen from above Pathology Anemia Host animal can lose 2000 pounds of blood in a season Dermatitis Inflammation, swelling, ulceration and itching around bite Tick Paralysis Tick imbeds at base of skull Toxic secretions released by tick causes swelling and temporary paralysis of host Paralysis disappears when tick is removed Infection 1 of 6

Many are important vectors of diseases in humans and domestic animals Ixodes sp. Largest genus with 200 species 40 in North America Important vector of disease Lyme Disease – caused by spirochaete Borrelais burgdorferi Tick-borne encephalitis Human granulocytic erlichiosis – caused by Erlichia sp. bacteria Dermacentor sp. Most important genus medically 30 species with 7 in North America Vector for several human diseases Tick paralysis Powassan encephalitis virus Colorado Tick Fever Rocky Mountain Spotted Fever Tularemia Also vectors for disease among domestic animals Hyalomma sp. Very difficult to identify to species Fairly large ticks Very hardy Found in deserts with little shelter Will bite humans and domestic animals Important vector for disease Can be carried to other continents by migratory birds Crimean-Congo hemorrhagic fever spreads between Africa and Europe Carries West Nile Virus Also can transmit Siberian tick typhus, boutenneuse fever, Q Fever, and Ehrlichiosis Boophilus sp. Very small ticks when not engorged Spread with the spread of the cattle industry Primarily use cattle as hosts Will bite humans Important vector for Texas Cattle Fever Caused by Babesia bigemina, a Protozoan related to the malarial parasites Now eradicated in U.S. Important vector for Crimean-Congo hemorrhagic fever and several other viruses in humans Family Argasidae Soft ticks About 160 species total Not vectors for disease Five genera Antricola and Northaspis found on cave-dwelling bats in North and Central America Ornithodoros Over 100 species Parasitize mammals, including bats and humans Vector for relapsing fever in humans O. cariaceus will give nasty bite to humans Otobius – spinous ear ticks Adults do not feed; only mate, lay eggs and die Argas

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Mostly parasites of birds and bats Spends time in animal’s bedding Will bite humans Order Mesostigmata Easily recognized by spiracle just behind third coxa of third pair of legs Four families are parasitic Family Laelaptidae Large number of diverse genera Usually Ectoparasite of mammals Some on invertebrates Do not transmit disease to humans May cause dermatitis Family Halarachnidae Parasite of the respiratory system of mammals Pneumonyssus sp. are found in primates But not in humans Raillietea auris lives on ears of cattle Lives on dead cells and secretions of ear Family Dermanyssidae Parasites of vertebrates Very important economically and medically Dermanyssus gallinae – Chicken mite Common on domestic fowl Chickens, turkeys, pigeons Feed at night Hide in crevices during the day. Can kill chickens and chicks in large infestations Will bite humans Attracted to warm objects May carry western and St. Louis equine encephalitis but transmission to mammals unlikely Liponyssus sanguineus – House Mouse Mite Feed on mice but will bite humans Transmits Rickettsial pox to humans Not fatal but makes you sick for weeks Ornithonyssus bacoti – Tropical Rat Mite Most common in mice and rats Can cause severe declines in laboratory rodents Will attack humans with painful bite Some people develop severe dermatitis Does not transmit diseases to humans Does transmit filarial worm to rats Family Rhinonyssidae All are parasites in respiratory tract of birds Nasal mites Feed on blood and tissue Probably very important vector of disease in wild bird populations Order Prostigmata Spiracle is variable in position Not as hard (schlerotized) as other mites Many feed on plants. Only a few are parasitic on animals Also free-living forms in terrestrial and aquatic habitats

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Family Cheyletidae Most are yellow or reddish and round Except mites on feathers which are elongated Cheyletiella yasguri – common on dogs C. blakei – common on cats Both can cause mange dermatitis Rarely bite humans Family Pyemotidae Parasitize insects that feed on grain Bite humans when they harvest grain or sleep on straw mats Pyemotes tritici – straw itch mite Females reach 1 mm in length Males smaller Normal host is grain beetle but will bite people Family Psorergatidae Small to medium size mites Create intense itching Psorergates ovis – itch mite of sheep P. simplex – itch mite of mice P. bos – itch mite of cattle. Family Demodicidae Follicle mites Cigar-shaped, very small mites 100-400 um long with stumpy legs Humans host two species Demodex folliculus Live on hair follicles Demodex brevis Live in sebaceous glands Live mainly on face, particularly around nose and eye Little pathology Incidence increases with age Demodex canis Serious pathogen on dogs Causes Red Mange, with the help of bacterium Staphylococcus pyogenes Can be fatal in young dogs Demodex canis Serious pathogen on dogs Causes Red Mange, with the help of bacterium Staphylococcus pyogenes Can be fatal in young dogs Dogs that recover may be permanently hairless! Family Trombiculidae Chiggers 1200 species Most described from larva Adults and nymphs are unknown for many species Only larval stage are parasitic Nymphs and adults feed on terrestrial invertebrates Cause chigger dermatitis Vector for disease Adults are very large, covered in velvet-like setae and are red or yellow Chigger Dermatitis

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Trombicula sp. in U.S, Leptotrombidium outside U.S. Larvae do not burrow into skin Mouthparts penetrate dermis and it injects salivary secretions Particularly proteolytic enzymes Digests the cells Secretions cause cells of host to harden into tube Larvae sucks juices of digested cells until engorged and drop off Bites are concentrated where clothes restrict chigger movement Some people are sensitive to the salivary secretions Creates severe reaction around bite Intense itching Can lead to secondary bacterial infections Scrub Typhus Caused by Rickettsia tsutsugamushi, a bacterium Carried by Leptotrombidium sp. Transmitted from adult female to larvae in egg Wild rodents are reservoir Found in Southeast Asia, islands of the Indian and Pacific Ocean, and Australia Symptoms Lesion forms around chigger bite Enlarges slowly to 8-12 mm with necrotic center Rash appears and spreads to extremities Delirium and other nervous disturbances follows Mortality ranges from 6% to 60% without antibiotics Order Astigmata Lack tracheal system Absorb oxygen through skin Very small Little hardening of exoskeleton Soft bodied Very important medically and economically Frequently cause various types of mange in domestic animals Family Psoroptidae Do not burrow into skin Pierce skin at base of hairs Causes inflamation that can be severe Choroptic mange Caused by Chorioptes bovis Formerly divided into many species based on host it was on Most common feet and hind legs Can cause seminal degeneration in sheep Family Psoroptidae Otodectes sp. Fairly common in dogs, cats, and other mammals. Live in the ears Cause intense itching Psoroptic mange Caused by Psoroptes sp. Pierces skin and sucks exudate Forms a scab that covers mite Mites then thrive and reproduce into millions in a few days Can greatly affect wool production 5 of 6

Most common in wooly area Very common in domestic animals and wild animals Family Sarcoptidae Sarcoptes scabiei Has been divided into many species but probably all the same species Causes sarcoptic mange in mammals Causes Scabies in humans When human comes in contact with mangy animal Adults mate on host skin Then females burrow into skin Males and nymphs stay on surface Tunnels through the upper layer of skin, laying eggs and feeding Larvae crawl back out onto surface Causes intense itching along burrows Can result in secondary bacterial infection Family Pyroglyphidae Most are free-living Many cause house dust mite allergies Live in the house, feeding on debris Mite parts, excrement are inhaled, resulting in allergic reaction Dermatophagoides scheremetewski Causes severe dermatitis on scalp, face, and ears of humans Normal host is probably sparrows, bats or other animals Feather Mites Feed on feathers and lipids used to waterproof feathers Wide variety of genera from many different orders of mites Cause very little damage and rarely carry disease Very important for taxonomy Transferred from parent to offspring Speciation occurs faster in mites than birds

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