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Tick-associated Infections

Ticks are obligate blood-sucking members of class Arachnida (arthropods -mites, spiders, scorpions)

Two families of are known to transmit disease to humans

Ixodidae: Hard ticks (egg, larva, nymph, adult)

Argasidae: Soft ticks

Ixodidae: These ticks remain attached for hours to days during Lyme Disease blood meal. 3 out of 13 genera transmit disease to humans




Argasidae: 1/5 genera transmit disease to humans, Lyme disease, lime disease


Tularemia: Clinical Manifestations

Systemic disease, incubation: 1 to 21 days (average 3 days)

Local or generalized

Tularemia: Clinical Manifestations

Most consistent sign is fever (temperature >39.5C)

Symptoms/signs: Chills, headache, vomiting, diarrhea, fatigue, myalgias

Physical findings: Lymphadenopathy (regional), skin lesions, hepatosplenomegaly, pharyngitis

Skin lesions: Chronic erythema nodosum, erythema multiforme


Ulceroglandular (40%): Cervical lymphadenitis, papule is located distal to nodes

Glandular: Late suppuration (30%) - fluid is usually sterile

Oculoglandular: Painful conjunctivitis, preauricular nodes

Oropharyngeal: Ingestion of improperly cooked meats


Pneumonic: Aerosol or hematogenous spread; patchy infiltrate (74%)

Typhoidal: Hilar lymphadenopathy (32%) and similar symptoms

to sepsis_ Other Manifestations: Meningitis, osteomyelitis, pericarditis, peritonitis, hepatic abscess, rhabdomyolysis

Differential diagnosis: Cat-scratch disease, tuberculosis, toxoplasmosis, Yersinia, syphilis, EBV, HSV, Bartonella, actinomycosis, sporotrichosis

Tularemia: Treatment

Drug of choice: Streptomycin 30 mg/kg/day in two equal doses for seven days (until patient afebrile for five days) or twice daily for three days; then once daily 15-20 mg/kg for four days

Alternatives: Gentamicin (5 mg/kg/day in two to three equal doses, IV/IM)

Amikacin, chloramphenicol, tetracycline, erythromycin

Mortality is less than 1%

Prevention: Hunting precautions and avoidance; vaccine

Rickettsia: Microbiological Characteristics

Pleomorphic coccobacilli, obligate intracellular parasite (except Rochalimaea and Bartonella)

Contain both DNA and RNA, multiply by transverse binary fission, characteristic red color

Rickettsia: Microbiological Characteristics

Occur under natural conditions in mites, lice or fleas; humans are incidental hosts and do not contribute to survival