Pneumocystis: Introduction, Classification, Morphology, Pathogenicity Lab Diagnosis, Treatment, Prevention, and Keynotes

Introduction of Pneumocystis

It is thought to be a protozoan, usually found in animals and occasionally in men, especially in newborns and young children. It causes typical pneumonia ( interstitial plasma cellular pneumonia) which is often fatal. The parasites appear as small round ‘ cysts’ containing 8 uninucleated bodies inside the histiocytes. The mode of infection is not known, rats and mice are supposed to be the carriers of the organism.

  • Size of Parasite: 0.5-1.0µm in diameter
  • Site in host: Lungs
  • Mode of infection
  •   Portal of entry: Respiratory / inhalation
  • Causative agent: Cysts
  • Medium: Pulmonary exudates, droplets infection to close contact
  • Clinical symptoms: Infection is not know
  • Disease: Pneumonia

Morphology and Life cycle

  1. Rats, dogs and mice, and several domestic animals transmitted the disease. These parasites are common in infants and uncommon in adults. This parasite probably is of low virulence and multiplies to damaging proportions in hosts of lowered resistance. Thus, it is most commonly found in enfeebled, premature and malnourished infants, 2-3 months of age.
  2. This parasite is an extracellular parasite classed as a protozoan and is the cause of interstitial plasma cell pneumonia.
  3. The oval or round organisms are 1-2 m (0.5 – 1.0 µm) in diameter and are nucleated. Usually, eight of these daughter cells are found clumped together in a viscous capsule 6-9 µm in diameter. Multiplication occurs by binary fission. Transmission is probably by droplet to close contact.


Pneumonia (fatal), Pneumocystis: In man, clinical infections are primarily found in infants. The lungs of children with this disease are firm and the cut surfaces are gray and airless. Microscopically, the most striking change is the thickened alveolar septum; infiltration with plasma cells, hence the name interstitial cells pneumonia. The alveolar epithelium is thickened, and alveoli are filled with fat-laden cells, parasites, and exudates giving a foamy appearance. Up to 78% of the entire lung space may be occupied by distended plasma cells.

Laboratory Diagnosis

Laboratory diagnosis of Pneumocystis pneumonia (PCP) typically involves collecting and analyzing samples of respiratory secretions, such as sputum or bronchoalveolar lavage (BAL) fluid. Here are the common laboratory tests used for the diagnosis of Pneumocystis:

  1. Staining and Microscopic Examination: The most common method for diagnosing Pneumocystis pneumonia is by staining and examining respiratory secretions under a microscope. Special stains such as Gomori methenamine silver (GMS) or toluidine blue O can be used to visualize the Pneumocystis organisms.
  2. Polymerase Chain Reaction (PCR): PCR is a technique used to amplify DNA sequences and is a highly sensitive method for detecting Pneumocystis DNA in respiratory secretions. This test can detect the presence of Pneumocystis even when the organisms are not visible under a microscope.
  3. Immunofluorescence Assay (IFA): IFA is a test that uses antibodies to detect Pneumocystis antigens in respiratory secretions. This test is less commonly used than staining and PCR, but it can be useful in cases where other tests are inconclusive.
  4. Culture: It cannot be cultured in the laboratory using conventional methods, so this test is not routinely used for diagnosis.
  5. Blood Tests: Blood tests such as antibody tests or antigen detection assays are not reliable for diagnosing Pneumocystis pneumonia, but they can be useful for monitoring treatment response.

It’s important to note that laboratory tests for Pneumocystis can sometimes produce false-negative results, particularly in cases where the infection is mild or in patients who have recently started treatment. Therefore, a negative test result does not necessarily rule out the possibility of PCP, and clinical judgment should be used in conjunction with laboratory testing.


Pneumocystis is a type of fungal infection that can cause pneumonia in people with weakened immune systems. The treatment of this depends on the severity of the infection, the overall health of the patient, and other factors.

Here are some common treatments for PCP:

  1. Antibiotics: Antibiotics such as trimethoprim-sulfamethoxazole (TMP-SMX), pentamidine, or dapsone are often used to treat Pneumocystis infections. These medications can help kill the fungus and prevent the infection from spreading.
  2. Corticosteroids: Corticosteroids may be prescribed to reduce inflammation in the lungs and improve breathing. They are often used in combination with antibiotics.
  3. Oxygen Therapy: Oxygen therapy may be needed if the infection has caused severe lung damage and the patient is having trouble breathing. Oxygen can be delivered through a face mask or nasal cannula.
  4. Antifungal Medications: In some cases, antifungal medications such as amphotericin B may be used to treat Pneumocystis infections.
  5. Supportive Care: In addition to medication, supportive care may be needed to manage symptoms and complications of the infection. This may include hydration, pain relief, and respiratory support.

It’s important to consult with a healthcare professional for the appropriate treatment of PCP. Treatment may vary based on the severity of the infection and the patient’s overall health.

Prevention of Pneumocystis

Preventing Pneumocystis infection is important, especially for people with weakened immune systems. Here are some ways to prevent Pneumocystis infection:

  1. Prophylactic Antibiotics: People who are at high risk of Pneumocystis infection, such as those with HIV/AIDS or undergoing immunosuppressive therapy, may be prescribed prophylactic antibiotics such as trimethoprim-sulfamethoxazole (TMP-SMX) to prevent the infection.
  2. Good Hygiene: Practicing good hygiene can help prevent the spread of Pneumocystis. This includes washing your hands regularly, avoiding close contact with sick people, and covering your mouth and nose when coughing or sneezing.
  3. Avoiding Exposure: People with weakened immune systems should avoid exposure to sources of Pneumocystis, such as contaminated soil, bird droppings, or certain types of mold.
  4. Immune System Support: Maintaining a healthy immune system can help prevent Pneumocystis infections. This includes getting enough sleep, eating a healthy diet, exercising regularly, and managing stress.
  5. Vaccination: There is no vaccine currently available for Pneumocystis, but vaccination against other infections such as influenza and pneumococcal disease can help reduce the risk of complications and strengthen the immune system.

Keynotes on Pneumocystis

Here are some keynotes on Pneumocystis:

  1. Pneumocystis is a type of fungus that can cause pneumonia in people with weakened immune systems, such as those with HIV/AIDS, cancer, or undergoing immunosuppressive therapy.
  2. Symptoms of Pneumocystis pneumonia may include fever, cough, shortness of breath, chest pain, and fatigue. These symptoms can develop slowly over several weeks or come on suddenly.
  3. Pneumocystis pneumonia is typically diagnosed through a combination of a physical exam, chest X-ray, and laboratory tests such as a bronchoscopy or lung biopsy.
  4. Treatment for Pneumocystis pneumonia often includes antibiotics such as trimethoprim-sulfamethoxazole (TMP-SMX), corticosteroids, oxygen therapy, and antifungal medications.
  5. Prophylactic antibiotics may be prescribed to prevent Pneumocystis infection in people who are at high risks, such as those with HIV/AIDS or undergoing immunosuppressive therapy.
  6. Good hygiene practices, avoiding exposure to sources of Pneumocystis, immune system support, and vaccination against other infections can all help prevent Pneumocystis infection.
  7. People with weakened immune systems, such as those with HIV/AIDS or cancer, are at higher risk of developing Pneumocystis pneumonia and should take extra precautions to prevent the infection.
  8. Early diagnosis and prompt treatment of Pneumocystis pneumonia are important to prevent complications and improve outcomes.
  9. It’s important to consult with a healthcare professional for personalized recommendations on how to prevent and treat Pneumocystis based on individual health status and risk factors.
  10. With appropriate treatment and management, most people with Pneumocystis pneumonia can recover fully, but the condition can be serious and even life-threatening in people with weakened immune systems.

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