Pneumocystis jiroveci

Pneumocystis jirovecii, formerly known as pneumocystis carinii has been renamed to differentiate it from the Pneumocystis that causes infection in mice. The Mouse Pneumocystis is now called P carinii, while the species that cause human disease has been renamed, Pneumocystis jirovecii.

It is not the only change that happened to this pathogen. It was previously considered to be a protozoa. However, now it has been reclassified as fungus. Its wall is consist of beta-D-glucan and chitin.

It has two forms - a trophic form and a cyst form.

It was first described in Europe during 2nd WW causing infection in malnourished children. Then in 1960s it was associated with haematological malignancy, and in 1980s - HIV.

We can get an idea from its history about the risk factors. We can divide them into a few groups.

1. Children group - Malnutrition, primary immunodeficiency (like SCIDS)

2. Malignancy group - Solid tumour, multiple myeloma, haematological malignancy. Haematological malignancies have a higher risk than other types of malignancy.

3. Transplant group - SOT, HSCT, organ rejection. Amongst HSCT, the allogenic transplant has a higher risk esp in the first 9 months. Amongst the SOT, the risk is highest in the first 6 months post-transplant and in heart-lung transplants and lowest in renal transplants.

4. Vasculitis group - inflammatory disease - dermatomyositis etc

5. HIV

6. Immunosuppressive drugs - steroid (especially in combination like cyclophosphamide ), TNF alpha inhibitor (infliximab), fludarabine, alemtuzumab, Temozolomide etc.

Transmission is human to human. Up to 65% healthy individuals may have asymptomatic carriage. The carriage has been associated with COPD.

Pneumocystis pneumonia (PCP) may present with dry cough, shortness of breath, fever and dyspnoea on exertion (and in some cases at rest)

LDH

A non-specific marker. An increased LDH with a background of risk factors may suggest PCP. However, it could be elevated in other causes of lung damage like malignancy.

Beta-D-glucan

BDG can be used to diagnose PCP in the appropriate clinical setting. BDG could be elevated in other fungal infections as well. It has a good negative predictive value.

Radiology

Diffuse, bilateral, interstitial infiltrates (ground-glass pattern in CT) in the chest x-ray is the typical finding. There are many other types of findings (Lobar pneumonia, nodules, cavitation, pneumatocele, pneumothorax etc) that have been reported.

In patients on inhalation pentamidine prophylaxis, the upper lobar consolidation could be seen as pentamidine gets deposited in the lower parts of the lungs.

Microbiology

Preferred sample - bronchoalveolar lavage, induced sputum, lung biopsy

Test -

• Direct fluorescent antibody staining (used to be the common test in the NHS, now being replaced by PCR)

• PCR

Preferred drug

Cotrimoxazole 15 to 20 mg/kg (based on trim) in 3-4 divided doses PO or IV.
Nowadays, many papers coming up advocating lower doses, but they are not established practice yet.
Monitor potassium level.

If cotrimoxazole allergy - Consider desensitisation.

Alternative drugs

• Atovaquone

• Primaquine+ clindamycin (preferred in mod-severe disease)

• Trimethoprim + dapsone

• Inhalation pentamidine

Duration

21 days.