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Biology of Ticks and Mites. L. Hannah Gould, MS, PhD Bacterial Diseases Branch Division of Vector-Borne Infectious Diseases Centers for Disease Control and Prevention Fort Collins, CO. Overview. Ticks, mites, and their identification Tick-borne diseases in the United States Lyme disease
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Biology of Ticks and Mites L. Hannah Gould, MS, PhD Bacterial Diseases Branch Division of Vector-Borne Infectious Diseases Centers for Disease Control and Prevention Fort Collins, CO
Overview • Ticks, mites, and their identification • Tick-borne diseases in the United States • Lyme disease • Rocky Mountain Spotted Fever • Ehrlichiosis • Babesiosis • Tularemia • Tick-borne relapsing fever • Mites
Ticks and Mites • Not insects • Four life stages • Egg • Larva (6 legs) • Nymph (8 legs) • Adult (8 legs) • Ticks: ≈ 80 species in US, 12 of public health/veterinary importance • Mites: 45,000 described species!
Ixodes scapularis • Blacklegged tick, deer tick • Transmits Lyme disease, babesiosis, ehrlichiosis • Found on eastern and north central United States • Feed on wide variety of mammals and birds
Dermacentor variabilis and D. andersoni • Dog tick, wood tick • Vector of Rocky mountain spotted fever, tularemia • Widely distributed, common • Adults feed on dogs, other medium to large mammals; larvae/nymphs feed on small rodents
Amblyomma americanum • Lone star tick • Vector of human monocytic ehrlichiosis, STARI • Widely distributed in southeastern US, Atlantic Coast • Wide host range
Soft Ticks • Take brief (< 30 minute) blood meals at night • Vector of tick-borne relapsing fever • Widely distributed • Wide host range • Live in burrows, caves, nests Soft tick, Carios (Ornithodorus) kelleyi
Lyme Disease • Identified in 1976 • Caused by Borrelia burgdorferi • Transmitted by Ixodesscapularis and I. pacificus ticks • Reservoirs include small mammals and birds • Deer enhance tick populations, not a reservoir
Erythema migrans • Occurs in 60-80% of cases • ~7-14 days after tick bite • Expands over days • Rarely painful, puritic From: Nadelman RB, Wormser GP. Erythema migrans and early Lyme disease. Am J Med 1995; 98(suppl 4A): 15S-24S.
Reported Lyme disease cases by age and sex—United States, 2003-2005
Percent of reported Lyme disease cases by month of onset, U.S., 2003-2005
Reported Lyme disease incidence by county of residence—United States, 2005 Incidence per 100,000 persons
1997 2005 Incidence per 100,000 persons Lyme disease high incidence counties, Northeastern United States
Source: http://biology.usgs.gov/luhna/harvardforest.html Lyme Disease – Emergence Source: http://rockpiles.blogspot.com/2006_05_21_archive.html “In Connecticut, the number of deer has increased from about 12 in 1896 to 76,000 today.” [Kirby Stafford Connecticut Agriculture Experiment Station]
Reforestation, Deer Populations, and Lyme Disease Expansion The Lyme disease incidence is rising due to… • Overabundant deer populations • Increased numbers of ticks • Expansion of suburbia into wooded areas • Increased exposure opportunities Source: K. Stafford, CAES
Southern Tick-associated Rash Illness (STARI) • Causes rash similar to that of Lyme disease • Transmitted by Amblyomma americanum • Southeastern and south-central United States Photo: Wormser et al CID 2005
Rocky Mountain Spotted Fever (RMSF) • Caused by Rickettsia rickettsii • Transmitted most commonly by Dermacentor variabilis and D. andersoni • 250-1200 cases/year in United States
RMSF: Signs and Symptoms • Symptoms • Fever, chills, headache, malaise, myalgias • Rash appears on day 3-5 • Maculopapular and petichial – 1st on extremities • Untreated mortality 20%; treated mortality 3-5% Early (macular) rash on sole of foot Late (petechial) rash on palm/forearm
Ehrlichiosis (Anaplasmosis) Ehrlichiachaffeensis (Human Monocytic Ehrlichiosis) • Transmitted by Amblyomma americanum • Southeastern and south central United States E. ewingii • Rare, immunosuppressed patients • Few cases in central United States E. phagocytophila (Human Granulocytic Ehrlichiosis) • Approximately 1200 cases per year in United States • Northeast, upper mid-Western United States • Transmitted by Ixodes scapularis and I. pacificus
Ehrlichiosis (Anaplasmosis) • Ehrlichiachaffeensis (Human Monocytic Ehrlichiosis, HME) • Transmitted by Amblyomma americanum • Southeastern and south central United States • E. phagocytophila (Human Granulocytic Ehrlichiosis, HGE) • Approximately 1200 cases per year in United States • Northeast, upper mid-Western United States • Transmitted by Ixodes scapularis and I. pacificus • E. ewingii • Rare, immunosuppressed patients • Few cases in central United States
Distribution of 3 Tick Species for HME and HGA Ixodes scapularis Ixodes pacificus Amblyomma americanum Overlapping distribution (I. Scapularis and A. americanum)
Signs and symptoms Fever Malaise Headache Myalgia/Arthralgia Anorexia Chills/Sweating Nausea/Vomiting Rash Cough Diarrhea Abdominal pain Severe clinical spectrum Disseminated intravascular coagulation Pancytopenia Encephalitis Meningitis Pulmonary Infiltrates Gastrointestinal bleeding Respiratory failure Renal failure Fatalities Clinical Presentation of Human Ehrlichioses
Babesiosis • Caused by Babesia microti • Transmitted by Ixodes scapularis • Reservoir in white-footed mice • Northeastern and mid-Western US • Rare, few cases each year • Clinically more severe in immunocompromised and elderly
Tularemia • Caused by bacterium, Franciscella tularensis • Transmitted by: • Tick (Dermacentor variabils, D. andersoni, Ambloymma americanum) or deerfly bite • handling infected sick or dead animals • eating or drinking contaminated food or water • inhaling airborne bacteria • 200 cases per year in United States • Most cases in south-central and western United States • Symptoms dependent on the route of infection
Tick-borne Relapsing Fever(TBRF) • Caused by Borrelia hermsii, B. parkeri, B. turicatae • Transmitted by Ornithodoros spp. soft ticks • Ticks feed quickly and painlessly at night • Rodents are primary reservoirs • Sporadic cases in the western U.S. (~25/year) • Associated with rustic cabins, high altitude • Recurrent fevers
Reported Cases of Tick Borne Relapsing Fever by County-- United States, 1990-2000 Number of Cases: Arizona 11 California 82 Colorado 30 Idaho 19 Nevada 13 New Mexico 4 Oregon 3 Texas 18 Utah 6 Washington 60 Wyoming 1
Tick Paralysis • Caused by toxin produced by Dermacentor ticks • Acute, ascending, flaccid paralysis • Reversed upon removal of tick • May result in death if tick is not removed • More frequent in young girls
Tick Testing and Tick Bite Prophylaxis • Neither generally recommended following tick bites • For Lyme disease, tick bite prophylaxis (single 200 mg dose doxycycline) recommended only when: • Tick reliably identified and attached for ≥ 36 hours • Can be started w/in 24 hours • Infection rate ≥ 20% • Doxycycline not contraindicated • Always monitor site of tick bite and health closely following a tick bite
Vaccination against tick-borne diseases • Vaccine for Lyme disease removed from market in 2002 • Vaccines not available for other tick-borne diseases
Proper Tick Removal • Use fine-tipped tweezers to grasp tick close to skin • Pull tick’s body away from skin (avoid crushing head) • Clean skin with soap and water • Properly dispose of tick DON’T: use petroleum jelly, a hot match, nail polish, or other products to remove a tick.
Family Trombiculidae:Chiggers • Eastern US; most common in southern states • Larvae attach to skin for 4-6 days • Cause intense itching and dermatitis • Chigger mites can vector scrub typhus http://mdc.mo.gov/nathis/arthopo/chiggers/
Scabies • Scabies or Itch mite, Scarcoptes scabei • Close contact/crowded conditions • Female mites burrow into skin and lay eggs, larvae return to surface to molt • Finger webs, folds of wrists, bends of elbows/knees
Other Mites Causing Dermatitis • Many species cause dermatitis: • Chicken Mite • Northern fowl mite • Tropical rat mite • House mouse mite • Grain mite • Straw itch mite • Cause intense itching and irritation • Infestations common after floods, rat/bird control Ornithonyssus bacoti Tropical Rat Mite
Suspected Mite Dermatitis Images: L.H. Gould, 2005
House Dust Mites • Allergen-symptoms include sneezing, itchy, watery eyes, runny nose, respiratory problems, eczema and asthma • Require damp environment • Feed on dander • “Dust control” http://creatures.ifas.ufl.edu/urban/house_dust_mite_fig1.htm