Obligate Intracellular Obligate Intracellular PathogenPathogen

Obligate Intracellular Obligate Intracellular PathogenPathogenRickettsia Rickettsia

ChlamydiaChlamydia

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 ExamTue., 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