NTA Level 5 • Semester 1 • PST05103

Cholera and Plague

Pharmaceutical Microbiology • Source Session/Topic 18

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Session 18: Cholera and Plague

Total Session Time: 120 minutes

Pre-requisites

• Human anatomy and physiology

Students Learning Tasks

By the end of this session students are expected to be able to:

• Describe Cholera and Plague (causative agents, transmission, signs

and symptoms)

• Describe treatment, prevention and control of Cholera and Plague e

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Cause and Transmission of Cholera (10 minutes)

• Cholera is an acute gastrointestinal infection caused by Vibrio

cholerae.

• Cholera is transmitted by faecal-oral route through ingestion of

contaminated water or food by human faeces leading to severe diarrhoea

and emesis associated with body fluid and electrolyte depletion

• Vibrio cholerae is a Gram negative bacterium that is oxidase positive

and motile via a polar flagellum

STEP 3: Signs and Symptoms of Cholera (10 minutes)

• Cholera is characterized by

o Profuse watery diarrhoea, vomiting, severe dehydration and

muscular cramps, leading to hypovolemic shock and death

o The stool has a characteristic “rice water” appearance

▪ non-bilious, grey, slightly cloudy fluid with flecks of

mucus, no blood and inoffensive odour

• Cholera may result in the following complications

o severe dehydration

o shock

o renal failure

STEP 4: Treatment, Prevention and Control of Cholera (15 minutes)

• Treatment options

o Replacement of fluids and electrolytes

▪ Lactated Ringer solution or, Normal saline

▪ Oral rehydration salts (ORS) if patient can drink

o Antibiotics

▪ Macrolides e.g. erythromycin

▪ Sulphonamides –co-trimoxazole

▪ Fluoroquinolones e.g. ciprofloxacin

▪ Tetracyclines –doxycycline

o Vitamins and minerals

▪ Zinc

▪ Folic acid

• Prevention and control measures include;

o Drinking water from safe sources (taps, decontaminated deep wells,

bottles)

o Boiling or treating of water to kill bacteria and make it safe for

drinking and other domestic uses

o Washing hands with liquid soap and running water after visiting

the toilet, before preparing foods, and before eating

o Avoiding consumption of uncooked street food or cooked food that

is no longer hot.

o Avoiding consumption of street prepared fresh fruits

STEP 5: Cause and Transmission of Plague (30 minutes)

• Plague is an infectious disease of wild rodents transmitted from one

rodent to another and occasionally from rodents to humans by the bites

of an infected flea. It can also be transmitted to humans through

direct contact with infected materials or by inhalation

• Plague is caused by the bacteria Yersinia pestis which is short,

pleomorphic Gram-negative rod that can exhibit bipolar staining with

special staining such as Giemsa.

• The genus Yersinia where Y. pestis belongs, is in the family

Enterobacteriaceae

• The bacteria are catalase positive, oxidase negative, and

microaerophilic or facultatively anaerobic.

• The ability of this organism to be transmitted by aerosol and the

severity and high mortality associated with pneumonic plague make Y.

pestis a potential biological weapon.

• There are 3 forms of plague infection, depending on the route of

infection:

o Bubonic plague

▪ This is the most common, caused by the bite of an infected

flea

▪ Y. pestis, enters at the bite and travels through the

lymphatic system to the nearest lymph node, replicates itself

and causes the lymph node to be inflamed, tense and painful,

turning into open sores with pus

o Septicaemic plague

▪ This occurs when infection spreads through the bloodstream,

following untreated bubonic plague causing bleeding, tissue

necrosis and shock

o Pneumonic plague

▪ This is the most virulent form and is rare

▪ It is typically caused by spread to the lungs from advanced

bubonic plague

▪ However, any person with pneumonic plague may transmit the

disease via droplets to other humans

▪ Untreated pneumonic plague can be fatal

A bubo in bubonic plague

[pic]

• Life cycle

o When a flea feeds on a rodent infected with Y pestis, the ingested

organisms multiply in the gut of the flea and, helped by the

coagulase, block its proventriculus so that no food can pass

through.

o Subsequently, the “blocked” and hungry flea bites ferociously, and

the aspirated blood, contaminated with Y pestis from the flea, is

regurgitated into the bite wound.

o The inoculated organisms may be phagocytosed by polymorphonuclear

cells and macrophages.

o The organisms are killed by the polymorphonuclear cells but

multiply in the macrophages; because the bacteria are multiplying

at 37°C, they produce the antiphagocytic protein and subsequently

are able to resist phagocytosis

o The pathogens rapidly reach the lymphatics, and an intense

hemorrhagic inflammation develops in the enlarged lymph nodes,

which may undergo necrosis and become fluctuant

o Although the invasion may stop there, Y pestis often reach the

bloodstream and become widely disseminated.

o Hemorrhagic and necrotic lesions may develop in all organs;

meningitis, pneumonia, and serosanguineous pleuropericarditis are

prominent features

o Primary pneumonic plague results from inhalation of infective

droplets (usually from a coughing patient), and it is

characterized by hemorrhagic consolidation, sepsis, and death

[pic]

STEP 6: Signs and Symptoms of Plague (10 minutes)

• After an incubation period of 2–7 days, there is sudden onset of high

fever, chills, head and body aches and painful lymphadenopathy,

commonly with greatly enlarged, tender nodes (buboes) in the neck,

groin, or axillae. This is the bubonic form of the disease.

• Nausea, vomiting and diarrhoea may develop with the early septicemic

form of disease.

• Later, disseminated intravascular coagulation leads to hypotension,

altered mental status, and renal and cardiac failure. Terminally,

signs of pneumonia and meningitis can appear, and Y pestis multiplies

intravascularly and can be seen in blood smears.

• Primary pneumonic plague results from direct inhalation of organism

into the lung. Patients often have a fulminant course with chest pain,

cough, hemoptysis, and severe respiratory distress.

STEP 7: Treatment, Prevention and Control of Plague (10 minutes)

• Treatment

o Streptomycin

o Gentamycin

o Doxycycline

o Fluoroquinolones e.g. ciprofloxacin

• Prevention and control

o Inform people of the presence of zoonotic plague and advised to

take precautions against flea bites

o Do not handle animal carcasses and avoid direct contact with

infected body fluids and tissues

o Apply standard precautions when handling potentially infected

patients and while collecting specimens

o Vaccination: Not recommended expect for high-risk groups (such as

laboratory personnel who are constantly exposed to the risk of

contamination, and health care workers).

STEP 8: Key Points (5 minutes)

• Plague is an infectious disease of wild rodents transmitted from one

rodent to another and occasionally from rodents to humans by the bites

of an infected flea.

• Plague can also be transmitted to humans through direct contact with

infected materials or by inhalation

• Plague occurs in three distinct forms namely bubonic, septicaemic and

pneumonic plague

• Antibiotics are used in the treatment of plague

• Cholera is an acute diarrhoeal disease caused by Vibrio cholerae. It

is transmitted by the faecal-oral route.

STEP 9: Evaluation (5 minutes)

• What is plague?

• Explain the life cycle of Y. pestis

References

Hugo and Russell (2011), Pharmaceutical Microbiology 8th Edition, Willey-

Blackwel publications

Karen C. Carroll et al (2013); Jawetz, Melnick and Adelberg’s Medical

Microbiology 26th Ed. McGraw Hill Co. Inc.

Greenwood et al (2012); Medical Microbiology, 18th edition Churchill

Livingstone

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