Plague (Black Death)
Plague is an infectious disease caused by the bacterium, bacillus Yersinia pestis, usually found in small mammals and their fleas that affect humans and other mammals.
Plague disease is spread between animals via their fleas and it can transmit from animals to humans.
Humans usually become infected with plague after bitten by a rodent flea that is carrying the plague bacterium Yersinia pestis or by handling an infected animal with plague.
Plague is also known as “Black death”.
Epidemiological Triad
Agent – The causative agent of Plaque disease is bacterium Y. Agent Y. Pestis is present in infected rodents and their fleas.
The natural survival of plaque is wild rodents such as field mice, skunks, which are found in mountains, forests and deserts.
In India, the main reservoir of plaque is Tatera Indica not the Rattus rattus.
Host – Plaque can affect both the sexes and all ages of people. People, who are at risk, are hunters, harvestors and cultivators.
Bacteria is present in abundance in blood, spleen, liver and other viscera of infected person.
Bacteria is present in sputum of cases of pneumonic plaque.
Environment – Heavy rainfall, Human dwellings, rodent density area,Temperature of 20-25 degree C, Humidity of 60% or above.
Causes of Plague
Yersinia pestis, plague bacteria is transmitted to humans through the bites of fleas that have previously fed on infected animals, such as- Rats, Mice, Cats, Rabbits, Dogs, Voles.
The bacteria can also enter in body if a break in skin comes into contact with an infected animal’s blood.
Domestic dogs and cats may become infected with plague from bites of flea or from eating infected rodents.
Types of Plague Disease
Plague is divided into three main types –
1. Bubonic Plague
2. Septicemic Plague
3. Pneumonic Plague
The difference between these three forms of plague is the location of infection –
In pneumonic plague; infection is in the lungs,
In bubonic plague; lymph nodes, and
In septicemic plague; within the blood
Diagnosis is done by testing blood, sputum, or fluid from a lymph node
1. Bubonic Plague
Bubonic Plague occurs when human become bitten from infected flea bite or when handling infected tissue or body fluids of a plague infected animal. It results in primary bubonic plague or septicemic plague. Symptoms include swollen of lymph nodes.
People and animals being infected when to visit places where rodents have recently died from plague, there risk of being infected from flea bites.
Flea bite exposure can result in primary bubonic plague or septicemic plague.
Dogs and cats are also bring plague infected fleas into the home..
Cats are more susceptible to plague, and can be infected by eating infected rodents. Sick cats cause risk of transmission of infectious plague droplets to their owners or to veterinarians.
2. Septicemic Plague
Septicemic plague most commonly spread by bites from infected fleas. It is a life threatening infection of blood, when the Humans get bitten by infected flea or become infected when handling tissue or body fluids of a plague infected animal.
For example, a hunter skinning a infected animal without using proper protective measures may become infected with plague bacteria.
3. Pneumonic Plague
Pneumonic Plague occurs when inhalation of respiratory droplets or small particles from a patient has pneumonic plague.
Person with plague pneumonia, may cough droplets containing the plague bacteria into air, these bacteria-containing droplets are inhaled by another person t can cause pneumonic plague.
Typically this requires direct and close contact with the person with pneumonic plague.
Pneumonic plague can occur either by breathing of Y. pestis (primary) or as a result of septicemic spread of bacteria during bubonic plague (secondary).
Pneumonic plague, which mainly affects the lungs, is spread by inhaling infectious respiratory droplets into the air by a sick animal or person.
Mode of Transmission
1. Commensal rodents (rats and mice) – to rat fleas – to man
2. Wild rodent – to man
3. Man – to man
Plague bacteria can be transmitted to humans through –
Plague is spread between animals and humans by the bite of infected fleas, direct contact with infected tissues, fluid, and breathing of infected respiratory droplets.
1. Bite of infected vector fleas – Fleas bite
Plague is a serious bacterial infection; humans become contaminated primarily by the bite of infected fleas.
2. Contact with contaminated fluid or tissue
Through direct contact with infected materials, that fed on infected rodents or by humans handling infected animals.
Humans can become infected when handling unprotected contact with infectious tissue or body fluids, or contaminated materials of a plague-infected animal.
3. Infectious droplets – Transmitted from person to person
Inhalation of respiratory droplets or small particles from a patient with pneumonic plague, it affects the lungs.
Incubation Period
Incubation Period depend upon the type of plaque –
1. Bubonic plague
2. Septicaemia plague
3. Pneumatic plague
Human infected with Yersinia pestis often develop symptoms after an incubation period of 1 to 7 days.
Incubation period of Pneumonic plague can be 24 hours.
Clinical Manifestation
Symptoms of plague disease depend on how the patient exposed to the plague bacteria.
There are three main clinical forms of plague infection; bubonic septicaemic and pneumonic plague.
If the bubonic plague is left untreated, plague bacteria can invade into the bloodstream.
1. Symptoms of Bubonic Plague
Patients develop symptoms –
1. Sudden onset of fever and Chills
2. Headache
3. Fatigue or malaise and weakness
4. Muscle aches
5. One or more swollen, tender and painful lymph nodes (called buboes) – typically develop in the first week after you become infected
Buboes may be –
a. Situated in the groin, armpit or neck
b. About the size of a chicken egg
c. Tender and firm to the touch
2. Symptoms of Septicemic plague
Septicemic plague may develop from untreated bubonic plague occurs when plague bacteria multiply in bloodstream.
Signs and symptoms include –
1. Fever and chills
2. Extreme weakness
3. Abdominal pain
4. Diarrhea and vomiting
5. Shock
6. Possibly Bleeding from mouth, nose or rectum, or under your skin
7. Skin and other tissues may turn blackening and death of tissue (gangrene) occurs, especially most commonly on fingers, toes, and the nose.
3. Symptoms of Pneumonic Plague
Pneumonic plague is the most dangerous form of the disease and is the only form of plague that can be spread from person to person by infectious cough droplets affects the lungs.
This disease develops from inhaling infectious droplets or may develop from untreated bubonic or septicemic plague after the bacteria spread to the lungs, may cause respiratory failure and shock.
Signs and symptoms can begin within a few hours after infection, symptoms include –
1. High fever
2. Headache
3. Weakness
4. Nausea and vomiting
5. Developing pneumonia with –
a. shortness of breath
b. Difficulty breathing
c. Chest pain
d. Cough, with bloody mucus (sputum)
Pneumonic plague developed rapidly and may cause respiratory failure and shock within two days of infection. Pneumonic plague needs to be treated with antibiotics within a day after signs and symptoms first appear, if not treated may be fatal.
Pathophysiology of Plague
1. Plague bacillus, Y. pestis, enters at the bite site of human and travels through the lymphatic system to the nearest lymph node
2. Bacteria replicate itself and swollen one or more lymph nodes develop in the first week after you become infected
3. The lymph node then becomes inflamed, tense and painful, and is called a ‘bubo’
4. At progress stages of the infection, inflamed lymph nodes turn into open sores and filled with pus.
5. Bacteria spread, enter into blood stream causesepticemic plague
6. Bubonic plague progresses and spread to the lungs (severe type of plague called pneumonic plague)
Laboratory Investigation
To identify Y. Pestis bacteria take sample of pus from a bubo, blood or sputum.
1. Smears of fluids or sputum
2. Blood culture
3. Serological test – To detect Y. pestis antigen
4. Immunofluorescence microscopy test
5. Rapid dipstick test
Treatment
Cases detected with plaque should be treated with antibiotics. it can be easily treated with antibiotics
Antibiotic is effective treatment against plague bacteria and also use of standard preventative measures.
Antibiotic used in treatment – Streptomycin Tetracycline
Prevention and Control of Plague
1. Early diagnosis/ treatment
No effective vaccine is available for plague. Antibiotics treatment can help prevent infection if at risk of infection or have been exposed to plague.
2. Vaccination
Vaccination should be only for prevention of plaque. According to WHO, Plague vaccine is a vaccine used against Yersinia pestis to prevent the plague, not for control. The vaccine is a killed plaque vaccine.
Immunization schedule for prevention of Plaque
Vaccine Primary dose Booster dose Route
1st dose 2nd dose
Killed plaque 1.0 ml 1.5 ml 1.0ml S/C
Vaccine for males
Killed plaque 0.75ml 1.0ml 0.75ml S/C
Vaccine for females
The plague vaccine is given with an interval of 14 days between two doses and Booster is recommended 6 monthly to high risk people.
3. Chemoprophylaxis
All the personnel who come in contact with plaque should be given chemoprophylaxis. Personnel’s mainly are – doctors, nurses, family members.
The drug used for chemoprophylaxis is tetracycline or sulphonamides.
4. Rodent-proof your home
5. Keep your pets free of fleas.
6. Wear protective measures when handling potentially infected animals
7. Control of fleas – Use insect repellent
8. Disinfection of infected materials
9. Environmental sanitation
Proper disposable of food waste into the covered dustbins
Complications of Plague
Complications of plague may include –
1. Gangrene. Blood clots in the tiny blood vessels of fingers and toes that disrupt the flow of blood and cause that tissue to die. The portions of fingers and toes that have died, may need to be removed (amputated).
2. Meningitis – Plague may cause inflammation of the membranes that surrounds brain and spinal cord (meningitis).
Plague FAQ
1. What is plague?
Plague is a disease caused by bacillus Yersinia pestis bacterium. Plague is also known as “Black death”.
This disease spread between animals via their fleas and it can transmit from animals to humans.
2. How do people get infected with plague?
Humans infected with plague infection after bitten by a rodent flea that is carrying the plague bacterium Yersinia pestis or by handling plague infected animal.
3. What are the different types of plague?
There are three forms of Plague –
1. Bubonic Plague – infection is in lymph nodes
2. Septicemic Plague – infection within the blood
3. Pneumonic Plague – infection is in the lungs
4. How is plague treated?
Antibiotic is an effective treatment against plague disease. Antibiotic used in treatment ; Streptomycin ,Tetracycline
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