disease caused by Yersinia pestis involving rodents and fleas First recorded in China in 224 BCE Black death 14 th century in Europe 50 million deaths Transmitted by infected flea bites to humans ID: 912732
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Slide1
Plague
Slide2Introduction
Zoonotic
disease
caused by Yersinia pestis involving rodents and fleasFirst recorded in China in 224 BCEBlack death: 14th century in Europe; 50 million deathsTransmitted by infected flea bites to humansOccurs in many forms: -Enzootically -Epizootically -Sporadically -In epidemics
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Slide3Problem Statement
Often seen as a problem of past or an ancient disease
Continues to be a threat because vast areas exist where wild rodents are infected particularly in endemic countries
Predominantly a rural disease but there have been urban outbreaksIncluded as an agent of BioterrorismMajor concern in endemic countries -Inherent communicability -Rapid clinical course -High mortality if left untreated3
Slide4History
3 major pandemics have occurred worldwide
First as Justinian plague in 6
th century; claimed nearly a hundred million victimsSecond as Black death in 14th century in Europe; claimed nearly 50 million victimsThird in Hongkong in 18944
Slide5Problem statement
Currently, the three most endemic countries are the
Democratic Republic of the Congo, Madagascar, and Peru
From 2010 to 2015 there were 3248 cases reported worldwide, including 584 deaths (WHO)In 2015: Fifteen people have been infected with bubonic plague in United States (CDC); Four of those cases were fatalIn 2004, India reported a localised outbreak of bubonic plague in the Dangud village (8 cases; 3 deaths), district of Uttarkashi5
Slide6Global distribution of natural plague foci, March 2016 (WHO)
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Slide77
Slide8Epidemiological determinants
Agent factors
A. AgentYersinia pestis, is a gram negative, non motile, coccobacillus, that exhibits bipolar stainingOccur in abundance in buboes, spleen, blood, liver, other viscera & sputum Virulence: Exotoxin, endotoxin, fraction 1Plague bacilli can survive and multiply in soil of rodent burrows
B. Reservoir Of InfectionWild rodents are the natural reservoirs of plague; found in mountains, deserts, cultivated areas & forests
In India, the wild rodent,
Tatera
indica
is
main
reservoir & not the domestic rat
Disease maintained & spread by resistant species of wild rodents
C. Source Of Infection
Infected rodents, Fleas
& Case
of pneumonic
plague
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Slide9Host
factors
A. Age and Sex
All ages and both sexes are susceptibleB. Human activitiesHunting, grazing, cultivation, harvesting and construction activities offer opportunities for flea-man contactC. Movement of people Through transportation of rats & rat fleas & infected personsD. ImmunityMan has no natural immunityImmunity after recovery is relative9
Slide10Environmental factors
A. Season
Outbreaks usually seasonal in nature
In northern India, the “plague season” starts from September to May. With the onset of hot weather, the disease tends to die outIn south India, there is no definite plague season B. Temperature and humidityTemperature of 20-25 deg C and relative humidity of 60% and aboveC. RainfallHeavy rainfall tends to flood the rat burrows. Responsible for keeping certain states free from plague. E.g., W. Bengal.D. Urban and rural areasLess in towns due to untoward ecological conditions & lack of efficient flea vectorsE. Human dwellingsIn poor housing conditions rats & ratfleas occur all year round
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Slide11Vectors of plague
Most common & efficient vector is the rat flea,
X.
cheopisOthers: X. astia, X. brasiliensis, Pulex irritansBoth sexes bite and transmit the disease Blocked fleaA flea may ingest upto 0.5 cu mm of blood which may contain as many as 5000 plague bacilli The bacilli multiply in the gut of rat flea and may block the proventriculus so that no food can pass through
Bites & suck blood over & over again thereby regurgitating plague bacilli into the bite woundInfected flea may live for 1-4 years
Partially blocked flea is more dangerous
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Slide12Flea indicesUseful in evaluating the effectiveness of a spray programme
Total flea index:
Average no. of fleas of all species per rat
Cheopis index: More significant than total flea index - Average no. of X. cheopis per rat - If >1, indicative of potential explosiveness of situationSpecific %age of fleas: % of different species of fleas found on ratsBurrow index: Av. no. of free-living fleas per species per rodent burrow Flea indices do not in themselves indicate an imminent plague epidemic
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Slide13Human plague
Most frequently contracted from
A. Bite of infected flea
B. Direct contact with tissues of infected animalC. Droplet infection from cases of pneumonic plague13
Slide14Transmission cycles in plague
1.
Commensal
rats Rat fleas Man Basic cycle in epidemic bubonic plague2.Wild rodents Wild rodent fleas or direct contact Man3. Wild rodents, peridomestic rodents, commensal rodents Wild rodent fleas, peridomestic rodent fleas, commensal rodent fleas Man4. Man Human flea (Pulex irritans) Man5. Man Man
When primary case of bubonic plague develops secondary pneumonic plague; infects contacts through respiratory route
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Slide15Types Of Human Plague
3 types
A. Bubonic plague (IP: 2 to 7 days)
B. Septicaemic plague (IP: 2 to 7 days)C. Pneumonic plague (IP: 1 to 3 days)15
Slide16Bubonic Plague
Most common type
Infected rat flea usually bite on lower extremitiesBacilli proliferate in the regional lymph glandsTypical features-Sudden fever, chills, headache, prostrationPainful lymphadenitisWithin few days: Greatly enlarged tender lymph nodes (buboes) in groin, axillaBubonic plague cannot spread from person to person because bacilli are locked up in buboes
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Slide17Pneumonic Plague
Primary pneumonic plague is rare; Incidence < 1%
Generally follows as a complication of bubonic-
septicaemic plagueHighly infectious : Spread from man to man by droplet infection17
Slide18Primary
septicaemic
plague is rare, except for accidental lab infections
Bubonic plague may develop into septicaemic plague in face of an overwhelming infectionClinical signsSigns of sepsis ± buboNecrosis of extremitiesMicrothrombi block capillaries“Black Death”Mortality (untreated): 100%18Septicaemic Plague
Slide19Laboratory Investigations
1.
Staining:
Smear from clinical material (bubo fluid, sputum) fixed with alcohol & stained with Giemsa’s or Wayson’s stainBipolar bacilli2. Culture from blood (transport in Cary-Blair media)3. Serology from acute & convalescent specimens4. Other methods: Inoculation of guinea pigs or mice or immunofluorescent microscopic test19
Slide20Prevention and Control
1. Control of cases
a
. Early diagnosis: During epidemic situations, diagnosis can be made clinically “Rat falls” provide a useful warning of possible outbreaks Plague suspected humans and rodents must be examined bacteriologically to confirm the presence of plagueb. Notification: Case notification (Human or Rodent) is required by international health regulationsc. Isolation: All patients of pneumonic plague as well as suspects; Also for bubonic plague if possible
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Slide21d. Treatment:
Drug of choice is
Streptomycin
: 30mg/kg body weight daily i.m. in 2 divided doses for 7 to 10 days Tetracycline, orally, 30-40mg/kg body weight daily is an alternative drug and sometimes given in combination with streptomycin Gentamycin, 2mg/kg of body weight loading dose, then 1.7mg/kg body weight every 8 hours i.v Sulphonamides, used if other drugs are not availablee. DisinfectionSputum, discharges & soiled articles21
Slide222. Control of fleas
Most effective method to break the chain of transmission is destruction of rat fleas by insecticides
Should precede or coincide anti-rodent measures
DDT (10%) and BHC (3%), used as dustIn areas of resistance to one or both of these, dust of carbaryl (2%) or malathion (5%) is usedSpraying required upto radius of 5 miles around each infected locality
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Slide233.
Control of rodents
Continuous mass destruction of rodents is an important plague preventive measure
Long term policy for control of rodents should involve improvement of general sanitation, housing & quality of life23
Slide244.
Vaccination
Only for prevention & not for control To be effective, vaccination should be carried out at least a week before an anticipated outbreak and the vaccine should be given in 2 doses at 7-14 days gap subcutaneously Immunity starts 5-7 days after inoculation & lasts for about 6 months requiring boosters six-monthly For biologists, geologists & anthropologists & travellers to hyperendemic areas
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Slide255. Chemoprophylaxis
Highly recommended
Should be offered to all plague contacts, medical, nursing, and public health personnel exposed to the risk of infection
Drug of choice is tetracyclineFor adult dose is 500mg, 6 hourly for 5 daysCheaper alternative is sulphonamide, 2-3 g daily for 5-7 days25
Slide266.
SurveillanceEssential in areas where natural plague foci exist, or where there is history of past infection Should cover all aspects of rodent & human plague, e.g., microbiology, serology, entomology, mammalogy, epidemiology & ecology26
Slide277
.
Health education
Essential part of any plague control programmeEmphasis must be placed on the need for the prompt reporting of dead rats and suspected human casesMedical practitioners should keep plague in mind for differential diagnosis of any cases of fever with lymphadenopathy, or when multiple cases of pneumonia occur27
Slide28Epidemiological Investigations
Objective:
Determination of the source of infection & the distribution, prevalence, & potential spread of plague in human population
Must be based on direct contact with villages & other communities affected by plagueWHO should be informed promptly of the occurrence of any epidemic or isolated case of plague28
Slide29Thank you
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