Smallpox Sagar sharma B.Sc.MLT

Smallpox HistoryLast naturally-occurring case in 1977High (30%) case fatality rateCaused at least 500 million deaths in the 20th centuryRoutine vaccination in U.S. ceased in 1972

Smallpox MorphologyCaused by variola virusFamily PoxviridaeBrick shaped, DNA virus200 nm in diameter

Variola VirusOccurs in 2 strainsvariola major90% of cases are clinically characteristic30% case fatality ratevariola minorLess severe1% case fatality rate

Physical and chemical properties of variola virus Stable and if protected from sunlight may remain viable for months at room temprature .they are susceptable to UV light and other radiations.The entire multiplication of viruses takes place in the cytoplasm of infected cell .

Smallpox PathogenesisIncubation: 12-14 days (range 7-17d)Infection occurs after implantation of virus on the oropharyngeal or respiratory mucosaDay 3-4: viral multiplication in lymph nodes; asymptomatic viremiaViral spread to spleen, bone marrow, lymph nodesDay 8: secondary viremia followed by fever and toxemia

Smallpox Clinical Presentation

After incubation period, onset of high fever (usually not infectious)Malaise, prostration with headache and backacheRash develops 1-2 days later (infectious)First appears on tongue, mouth, oropharynxSpreads to face, forearms 2-3 days laterFinally appears on trunk and legsRash becomes vesicular then pustularMost infectious from rash onset to first 7-10 days of rashDeath from smallpox occurs in 2nd week of illness due to toxemia

Smallpox Rash

Stages of rash: maculopapular vesicular pustular

Smallpox rash has centrifugal distribution (i.e., most dense on face, then extremities)

Synchronous lesions (appear during a 1-2 day period and evolve at the same rate)

Smallpox Rash Progression4357913 Papules are seen on days 3 and 4; vesicles around day 5; pustules on days 7- 9. Scab formation is apparent on day 13.

Differentiating Smallpox from Chickenpox

SMALLPOX CHICKENPOX FEVER ONSET2 to 4 days before rashAt rash onset RASH EvolutionLesions at same stageLesions appear in cropsLesions evolve at same rateLesions in different stages DistributionRash centrifugalRash centripetalRash on palms and solesNever on palms or soles DevelopmentSlowRapidPox dont burst when probedLesions burst when probedMORTALITY30%Rare

Rash DistributionSmallpox lesions are concentrated more on the face, arms and legs

Smallpox TransmissionSmallpox spreads primarily through respiratory dropletsDirect contact and contaminated clothing, bedding can also spread infectionTransmission: rash onset scabs fall offWinter and early spring most favorable for spreadVirus inactivated within 1-2 days in event of aerosol release

Smallpox Laboratory ProceduresSpecimens should be collected by recently vaccinated personnel

Vesicular or pustular fluid, scabs, scraping of skin lesions, blood samples, tonsillar swabs

Diagnosis confirmed by PCR and electron microscopy

Cultivation and host range Chicken embryo : virus grows on the 11 to 13 days old chick embryo .Variola pocks are small , shiny , white ,convex , non necrotic , non hemorrhogic lesions Tissue culture :grown in the tisue cultures of monkey kidneys, HeLa and chick embryo cells .Eosinopphilic inclusion bodies can be demonstrated in stained preprations .

Animals : the variola virus only produces similar lesions in monkeys. Scarification of rabbit cornea with variola virus leads to keratitis .Intranasal installation of the variola virus in the monkey produces a self limited attack of small pox with generalized skin lesions.

Smallpox VaccinationRoutine vaccination of civilians stopped in the U.S. in 1972

Immune status of those previously vaccinated is unclear

Beginning January 2003 smallpox vaccination for certain military personnel and smallpox response teams starts

Current vaccine, Dryvax, is same vaccine used in 1970s and contains live virus (vaccinia)

Smallpox Vaccination Adverse Effects1/10,000 persons have serious side effects including:lymphadenopathyfeverencephalitis (1/300,000)progressive vaccinia (1/2,000)eczema vaccinatum (1/26,000)death (1-2/1,000,000)

Vaccine Contraindications (Pre-exposure)For Vaccinees and Potential ContactsImmunodeficiencye.g., HIV infection, AIDS, many cancers, lupusImmunosuppressive therapyCancer, transplants, steroid therapy*, topical steroids for skin dz, inhaled steroids**Eczema/Atopic DermatitisHx or presence of eczema, including healed eczema, atopic dermatitisSkin Disorders***Disruptive or eruptive, e.g., acne, burns, impetigo, zoster, wounds, contact dermatitis, current surgical incision woundsPregnancyCurrent or planning within 4 weeks of vaccinationCurrent nursingChild age 1 yr or less in householdEye disease of the conjunctiva or cornea (Vaccinee only)Pruritic lesions, florid inflammationAllergies to Dryvax vaccine components (Vaccinee only) Polymyxin B sulfateStreptomycin sulfateChlortetracycline hydrochlorideNeomycin sulfateTetracycline

Source: CDC

Preventing Contact TransmissionUntil a scab has formed:Vaccination site must be coveredNo touching, scratching, or rubbing vaccination siteAvoid person-to-person contact with susceptible personsAvoid touching, rubbing or otherwise performing any maneuvers that might transfer vaccinia virus to the eye or surrounding skinCarefully discard vaccination site covering After handling the vaccination site covering, thoroughly wash hands with soap and running water

References R Ananthanarayan.,&CK Jayaram Paniker(Eds.). (2005).Text book of microbiology (5th Ed.).India :Orientlongman.Smallpox. (2014, Aug15). InWikipedia, The Free Encyclopedia. Retrieved 10:40,Nov 15, 2014, fromhttp://en.wikipedia.org/w/index.php?title=Microtome&oldid=607775556

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