Obligate Intracellular Pathogen Rickettsia Chlamydia Family Rickettsiaceae: Genera • Zoonotic infection – Human microbial pathogens ~61% zoonotic – Rickettsia are arthropod-borne infections • Spotted Fever Group – Rickettsia rickettsii – Rocky Mountain spotted fever; rodent, tick • Typhus Group – Rickettsia typhi – Endemic typhus; rodent, flea – Rickettsia prowazekii – Epidemic typhus; mammal, louse Rickettsia: Gram Stain and Culture • Gram (-) small, pleomorphic coccobacilli • Gram stain poorly, observed by Giemsa stain of infected cell • Grow in phagocytic, nonphagocytic cells • Lab culture in embryonated eggs or cell tissue culture (similar for virus) • Cultivation costly and hazardous; aerosol transmission occurs easily Chlamydia, Rickettsia, Virus Rickettsia: Lab ID • Giemsa, or Immunofluorescence assay (IFA) - direct detection MO in tissue • Weil-Felix reaction – Nonspecific test – Rickettsial antibody agglutinate Proteus vulgaris – Presumptive evidence of typhus group infection – Not very sensitive or specific, many false positives • Agglutination or Complement Fixation (CF) assay - use specific Rickettsial antigen, test for infection and antibody Rickettsia: Virulence Factors • Induced phagocytosis, intracelluular growth – protected from host immune clearance • Replicates in endothelial cells – cell damage, vasculitis • Recruitment of actin - intracellular spread Rickettsia: Infection and Disease • Disease worldwide, USA • Arthropod reservoir/vector (tick, mite, louse, flea) • Diseases characterized by fever, headache, myalgias, usually rash R. rickettsii: Rocky Mountain Spotted Fever (RMSF) • USA ~500-1000 cases/year • Ticks must remain attach for hours • Incubation 7 days - headache, chills, fever, aching, nausea • Followed by maculopapular rash on extremities (including palms and soles), spread chest, abdomen • If untreated – Petechial rash, hemorrhages skin and mucous membranes – Vascular damage, MO invades blood vessels – Death up to 20%, due to kidney or heart failure Rocky Mountain Spotted Fever Rickettsia: Typhus Group • Incubation 5-18 days • Symptoms - severe headache, chills, fever, maculopapular rash (subcutaneous hemorrhaging as MOs invade blood vessel) • Rash begins on upper trunk; spread to whole body except face, palms of hands, soles of feet • Lasts ~2 weeks • Patient may have prolonged convalescence R. typhi : Endemic Typhus Fever • “typhus” “fever” • Disease worldwide in warm, humid areas (Gulf states, So Cal.; S. America, Africa, Asia, Australia, Europe) • Murine typhus - rat primary reservoir, transmitted to human by rat flea • Disease occurs sporadically • Clinically same, but less severe than epidemic typhus • Restricted to chest, abdomen; generally uncomplicated, lasts <3 weeks • Low fatality R. prowazekii : Epidemic Typhus Fever • • • • Disease C & S Americas, Africa; less common USA Human, squirrel primary reservoir Transmitted by louse; bites, defecates in wound At risk - people living in crowded, unsanitary conditions; often war, famine, natural disaster • Complications - myocarditis, CNS dysfunction • Mortality high untreated cases, up to 20% • Brill-Zinsser disease - individual may harbor MO, latent infection with occasional relapses Rickettsia: Treatment and Prevention • RMSF – Doxycycline drug of choice – Avoid ticks, wear protective clothing, use insect repellents, insecticides – In infested areas, check and remove ticks immediately • Typhus Fever – Doxycycline effective – Improve personal hygiene and living conditions, reduce lice by insecticides, control rodent population – Inactivated vaccine for epidemic typhus Family Chlamydiaceae: Genera • Chlamydia trachomatis – STD, eye infection • Chlamydophila pneumoniae – pneumonia • Chlamydophilia psittaci – pneunomia (psittacosis); birds, humans • Obligate intracellular parasite • Cell wall similar G(-) bacilli, lack peptidoglycan • Energy parasites, use ATP of host cell • Giemsa stain - Chlamydia inclusions in tissue Chlamydia: Life Cycle – Elementary Body (EB) • Circular, infectious form; 300-400 nm • Metabolically inactive • Resistant to harsh environments • 0 hour - EB binds to host cell, induced phagocytosis • Outer membrane of EB prevents lysosome fusion, survives in phagosome • 8 hours - EB reorganizes into Reticulate Body (RB) Chlamydia: Life Cycle – Reticulate Body (RB) • Noninfectious form, larger, less dense, 800-1000 nm • Metabolically active • 8-30 hours – Synthesize new materials – Multiply by binary division – Form inclusion body – Reorganize, condense into EB • 35-40 hours - cell lyses, releases EB, begins cycle again Chlamydia: Lab ID • Stain tissue – Giemsa stain – Direct fluorescent antibody (DFA) – ELISA – Less sensitive • Cell culture – More sensitive method – Grow MO in tissue culture, stain infected cells • DNA amplification test – Recently developed – Specific, sensitive – Now routine test of choice Chlamydia: Virulence Factors • Intracellular replication – protected from host immune defense • Prevent fusion of phagolysome – evades phagocytic killing • Repeated infections by C. trachoma result in cell pathology • Serotypes A-K and L1, L2, L3 - serotype identifies strain’s clinical manifestation Chlamydia trachomatis: Trachoma • • • • • • • • • “rough” “trachoma” granulations on conjunctiva Serotypes A-C Single, greatest cause blindness developing countries Infections mainly children (reservoir), infected first three months life Transmission eye-to-eye, direct contact (droplet, hand, clothing, fly) Chronic infection, reinfection common Conjunctival scarring, corneal vascularization Scars contract, upper lid turn in so eyelashes cause corneal abrasions Leads to secondary bacterial infections, blindness C. trachomatis: Lymphogranuloma Venereum • Serotypes L1, L2, L3 • Venereal disease, occurs developing, tropical areas • Primary stage - painless lesion (vesicle or an ulcer) occurs site of entry in few days, heals with no scarring; but widespread dissemination • Secondary stage - occurs 2-6 weeks later, symptoms of regional suppurative lymphadenopathy (buboes), may drain for long time, accompanied by fever and chills. Arthritis, conjunctival, CNS symptoms • Tertiary stage - urethrogenital perineal syndrome; structural changes, such as non-destructive elephantiasis of the genitals, rectal stenosis C. trachomatis: STD • Urogenital tract infection serotypes D-K • Major cause of nongonococcal urethritis; frequently found concomitantly with N. gonorrhoeae • In males - urethritis, dysuria, sometimes progresses to epididymitis • In females - mucopurulent cervical inflammation, can progress to salpingitis and PID • USA - #1 STD C. trachomatis: Inclusion Conjunctivitis • Newborns and adults • Genital tract infection source of eye infection (serotypes D-K) • Benign, self-limited conjunctivitis, heals with no scarring • Newborns infected during birth process: – 1-2 weeks, mucopurulent discharge – Lasts 2 weeks, subsides – Some develop afebrile, chronic pneumonia • In adults – causes an acute follicular conjunctivitis with little discharge Chlamydia: Treatment and Prevention • Genital tract infection and conjunctivitis: – Adult - azithromycin or doxycycline, prompt treatment of patients and partners – Newborn – erythromycin – Public Health education • Trachoma: – Need prompt treatment, prevent reinfection – Systemic tetracycline, erythromycin; long term therapy necessary – Improve living, sanitary conditions – Difficult to prevent endemic disease in developing countries due to lack of resources, medical care Chlamydophilia pneumoniae: RT Infection • Human pathogen; common infection, especially 6-25 yr. old • Most infections asymptomatic or mildly symptomatic • Sore throat, hoarseness, flulike symptoms • May cause sinusitis, pharyngitis, bronchitis, pneumonia • Accounts for ~10% hospitalized pneumonia Chlamydophila psittaci: Psittacosis • • • • • • “parrot” “parrot fever” Naturally infects avian species Mild to severe respiratory infections Human infection by contact infected bird Infection - subclinical to fatal pneumonia Commonly causes atypical pneumonia with fever, chills, dry cough, headache, sore throat, nausea, and vomiting Case Study 9 - Chlamydia • A 22-year-old man came to the emergency department with a history of urethral pain and purulent discharge that developed after he had sexual contact with a prostitute. Gram stain of the discharge revealed abundant gram-negative diplococci resembling Neisseria gonorrhoeae. The patient was treated with penicillin and sent home. Two days later, the patient returned to the emergency room with a complaint of persistent, watery urethral discharge. Abundant white blood cells but no organisms were observed in Gram stain of the discharge. Culture of the discharge was negative for N. gonorrhoeae but positive for C. trachomatis. Case Study 9 - Questions • 1. Why is penicillin ineffective against Chlamydia? What antibiotic can be used to treat this patient? • 2. Describe the growth cycle of Chlamydia. What structural features make the EBs and RBs well suited for their environment? • 3. Describe the differences among the three species in the family Chlamydiaceae that cause human disease. Class Assignment • Textbook Reading – Chapter 40 Zoonotic and Rickettsial Disease • The Rickettsiaceae • Omit: Remaining last two Sections of reading • Omit: Key Terms, Learning Assessment Questions – Chapter 24 Chlamydia, Mycoplasma, and Ureaplasma • Chlamydia • Key Terms • Learning Assessment Questions Final Exam Tue., March 20, 2012 8:30 – 10:30 am • Mycobacterium thru Ureaplasma • Lecture, Reading, Key Terms, Learning Assessment Questions • Case Study 7, 8, 9, 10 (Mycobacterium, Clostridium, Chlamydia, Legionella) • Exam Format: – Multiple Choice – Terms – True/False Statements – Short Essay • Review, Review, Review! • Repetition is the key to retention