Purshotam Kumar Sah Kanu's document provides an overview of plague caused by the Yersinia pestis bacterium. Some key points: - Plague is transmitted from rodents to humans by flea bites and can cause bubonic, septicemic, or pneumonic infections in humans. Left untreated it has a high fatality rate. - There have been three major plague pandemics in human history dating back over 2000 years that killed tens to hundreds of millions. The causative bacterium was isolated in 1894. - Currently most cases are reported in developing countries in Africa and Asia. Treatment involves antibiotics like streptomycin for 10 days or until fever subsides to prevent spread.

1. PLAGUE
Name: Purshotam Kumar Sah Kanu
Roll No.: MB 1318/075
Level: M.Sc Microbiology (3rd Sem)
Central Department of Microbiology
Tribhuvan University, Kirtipur
Kathmandu, Nepal

2. Introduction
• Plague, infectious disease caused by Yersinia pestis, a bacterium transmitted from
rodents to humans by the bite of infected fleas, direct contact with infected fluids
or tissue from a host inhalation of respiratory droplet.
• The bacteria, the animal reservoir and the vector in a given area are collectively
called a “plague natural focus”.
• Plague is a fatal disease, which approximately more than 200 million people have
been dead by this disease.

3. History
• Plague recorded more than 2000 years ago.
• Three pandemics:
• 1st 542 AD; Justinian plague;100 million dead in 60 years from N. Africa.
• 2nd 14th century; Black death; 25 million dead in Europe alone.
• 3rd ended in 1990s; Burma to China(1894) and Hong kong to other continents
including N. America via rat infected ships; 20 million dead in India alone.
• By the end of the 19th century, the germ theory of disease had been put on a sound
empirical basis by the work of the great European scientists Louis Pasteur, Joseph
Lister, and Robert Koch.

4. • In 1894, during the epidemic in Hong Kong, the organism that causes plague was
isolated independently by two bacteriologists, the Frenchman Alexandre Yersin,
working for the Pasteur Institute, and the Japanese Kitasato Shibasaburo, a former
associate of Koch. Both men found bacteria in fluid samples taken from plague
victims, then injected them into animals and observed that the animals died
quickly of plague.
• Yersin named the new bacillus Pasteurella pestis, after his mentor, but in 1970 the
bacterium was renamed Yersinia pestis, in honour of Yersin himself.

5. Epidemiology
• Internationally, cases of plague are typically reported from developing countries in
Africa and Asia.
• From 1990-1995, 12, 998 cases worldwide were reported to the World Health
Organization (WHO), particularly from countries such as India, Zaire, Peru,
Malawi, and Mozambique.
• In 2003,2118 cases were reported with 182 deaths worldwide.
• 98.7 percent of cases and 98.9 percent of deaths were reported from Africa.
• Australia is the only continent that has never report a case of plague.
• In the United states, natural Y. pestis loci exist in primarily rural and uninhabited
areas.

6. • 10-15 cases of plague on average are reported each year in the united states.
• In the early twentieth century, plague epidemics accounted for about 10 million
deaths in India.
• As reported in National Geographic, mass graves of plague victims were
discovered in an area of Venice called “Quarantine island.”
• In recent years, and with the potential threat for bioterrorism, the centers for
Disease control and Prevention (CDC) has specified Y. pestis as a Category A
bioterrorism agent.

7. Plague in Nepal
• It was first recorded only between 1960-1962, in Rupandehi and Mahottari
districts with 150 cases.
• Later, it was reported again in October 1967, in Nawra village of Bajhang.
• It was reported that the plague was airborne and resulted in six cases of tonsillar
plague, one case of primary pneumonic plague, and 17 cases of bubonic plague.

8. Causative Organism
• The disease is caused by the Plague bacillus, rod shaped bacteria referred to as
Yersinia pestis (family enterobacteriaceae).
• It is a non-motile, pleomorphic, gram negative coccobacillus that is non
sporulating.
• It is facultative anaerobe.
• It can infect human and animals via the oriental rat flea which called (Xenopsylla
Cheopis).
• It can reproduce inside cells, so even if phagocytosed they can still survive,
because it produces an anti-phagocytic slime layer.

9. Pathogenesis
• Colonization and growth of Y. pestis in the flea proventriculus (valve between
oesophagus and midgut) blocks passage of food, which results in efficient
transmission via flea bite.
• Phospholipase D helps the bacteria to withstand antibacterial factors active in the
flea midgut and haemin storage locus (hms) is required to colonize and for biofilm
formation in the flea.
• Y. pestis disseminates from the site of infection within macrophages and this
requires a plasminogen activator.
• Once phagocytized the disease progresses the same from bite or ingestion or
inhalation.

10. • There are two stages of Y. pestis proliferation in the host.
• Neutrophils kill the bacteria, but macrophages phagocytize them but do not kill
them and there it grows intracellularly within spacious vacuoles.
• In susceptible hosts, infected macrophages are carried to the lymph nodes --hence,
buboes-- and the liver and spleen, where the bacteria cause the macrophages to
lyse.
• Then, the bacteria grow extracellularly. Extracellular growth requires plasmid
encoded Type III secretion system and translocation of Yersinia outer protein
(Yops).
• Yops interfere with immune cell function and can cause immune cell death by
apoptosis. LcrV (V antigen) has anti-inflammatory activity.
• These virulence factors allow massive extracellular proliferation of the bacteria in
affected tissues.

11. Infectious dose, Incubation, Colonization
• In humans, the infectious dose of Y. pestis has been estimated to range from 100
organisms to 20,000 organisms.
• The incubation period of the bubonic, septicemic, and pneumonic plague types
ranges from 2-6 days.
• Y. pestis colonizes macrophages, reaches lymph nodes, escapes the macrophages,
and proliferates extracellularly.
• Left untreated, Y. pestis is able to spread to the bloodstream and cause secondary
infection as well as septicemic plague in rare cases.
• Y. pestis is also able to colonize lung tissue as pneumonic plague.

12. Mode of transmission in humans
• Air droplet
• Direct physical contact
• Indirect physical contact
• Fecal-oral transmission
• Vector borne transmission

13. Virulence factors
• Plasminogen activator: facilitates the adhesion and invasion of the bacterium to
the extracellular matrix of the host tissue.
• Siderophores: Yersiniabactin(Ybt); organism capable of scavenging
iron from human and of enhanced growth.
• Anti-phagocytic antigens: Factor 1 (f1) and V antigen increases Y. pestis
resistance to phagocytosis by macrophages.
• Type III secretion system: Y.pestis utilizes a T3SS in order to evade host immune
responses.

14. Clinical Features
The symptoms of Y. pestis present in different
ways:
Bubonic plague
oIt usually results from the bite of an infected
flea or by introduction of contaminated fluid or
tissue into an open wound.
oAfter an incubation period of 2 -6 days, there
is acute onset of symptoms such as fever,
headache, chills and weakness.
oIt is also common to see gastrointestinal
symptoms like nausea and vomiting.
oAbout 24hrs after start of these symptoms,
swollen, extremely tender lymph nodes known
as buboes, filled with multiplying Y. pestis
appear.
oThese buboes typically form from lymph
nodes that were closet to the site of infection.

15. Septicemic Plague
 When the bacteria enters the blood stream
directly and multiply there, it’s known as
septicemic plague.
 It can either develop primarily, often
through the introduction of contaminated
fluid or tissue into an open wound or
secondarily as a result of untreated
bubonic plague.
 There is a sudden onset of symptoms
including fever, chills, nausea and
vomiting.
 Later on in the course of the disease
purpura, a rash caused by bleeding into
the skin and disseminated vascular
coagulation can develop.
 Tissue blackening and death specially in
the fingers, toes and the nose is also seen.

16. Pneumonic Plague
• It is a highly contagious form of the disease. Primary pneumonic plague develops
when a person inhales infectious droplets emitted by a pneumonic plague sufferer.
• Secondary pneumonic plague can develop when untreated bubonic or septicemic
plague spreads to the lungs.
• Symptoms include fever, headache, weakness and a developing pneumonia which
includes symptoms of cough, chest pain and shortness of breathe.
• As the disease progresses, hemorrhages, necrosis of the tissue and pulmonary
abscesses are other common symptoms.
• In the end stages of untreated pneumonic plague, Adult Respiratory Distress
Syndrome (ARDS) and shock can sometimes be seen.

17. Diagnosis
Specimen: Pus or fluid, Sputum, blood, throat swab
or washings, skin swabs and scrapings are also
collected.
Microscopy: Gram staining, methylene blue and
giemsa’s staining of sputum and aspirate from lymph
node show bacilli with bipolar staining.
Culture: Trypticase soy agar with 5% sheep blood
and incubated for 24hrs at 28°C
The colonies should be gray-white, translucent, little
to no hemolysis and be non lactose fermenter.
It should test positive for catalase, but negative for
oxidase, urease and indole test.
Serological test: antibodies to F1 antigen appear
towards the end of first week of the illness and may
be detected by passive haemagglutination, ELISA or
complement fixation test.

18. Treatment
• Streptomycin is the antibiotic of choice for treating Yersinia pestis infections.
• Other possible antibiotics include gentamicin, chloramphenicol, tetracyclines, and
fluoroquinolones.
• The antibiotic levofloxacin has also been recently approved by the Food and Drug
Administration as appropriate treatment.
• Antibiotic dosages are typically administered for the full period of ten days or for
three days after the fever has subsided.
• It is also important to hospitalize and quarantine any suspected or confirmed cases
of Yersinia pestis in order to provide effective treatment and prevent the spread of
the disease if it develops into secondary pneumonic plague.

19. Prevention and control
• Diminish the possibility of rodent infestation around homes by clearing away
cluttered debris and apply flea control products for pets that roam freely in the
open.
• Means of prevention can also be applied in hospital settings where the possibility
of transmission can be high.
• Standardized procedures of handwashing and utilization of gowns, latex gloves,
and protective devices should be followed to protect all body orifices from coming
into contact with Y. pestis.
• Restrictions of patients suspected with plague should be enacted to prevent the
spread of disease to other individuals.

20. BIBLIOGRAPHY
• Park K. (2015) Park’s Textbook of Preventive and Social medicine,23rd Edition.
Bhanot, India.
• https://www.cdc.gov/plague/transmission/index.html
• https://www.who.int/news-room/fact-sheets/detail/plague
• https://microbewiki.kenyon.edu/index.php/Yersinia_Pestis_(Pathogenesis)
• https://english.onlinekhabar.com/history-of-epidemics-in-nepal-part-i-6-deadly-
diseases-that-killed-hundreds.html
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2427975/pdf/bullwho00199-
0004.pdf