Pneumocystis jirovecii
Pneumocystis pneumonia (PCP) is a severe lung infection caused by the fungus Pneumocystis jirovecii, primarily affecting individuals with weakened immune systems, such as those with HIV/AIDS, cancer patients undergoing chemotherapy, and organ transplant recipients. In healthy individuals, this fungus resides harmlessly in the respiratory tract, but in immunocompromised patients, it can lead to life-threatening pneumonia. Symptoms of PCP include shortness of breath, fever, nonproductive cough, and rapid heart and breathing rates. Diagnosis typically involves observing the fungus in respiratory fluid, supported by imaging techniques like chest X-rays or CT scans. Treatment options include antibiotics like trimethoprim-sulfamethoxazole, with alternatives for those allergic to sulfa drugs. Preventative measures, known as chemoprophylaxis, are crucial for at-risk patients, particularly those with HIV. The high mortality rate associated with untreated PCP underscores the importance of early diagnosis and intervention.
Pneumocystis jirovecii
Disease/Disorder
Also known as:Pneumocystis carinii
Anatomy or system affected: Chest, lungs, respiratory system
Definition: A small fungus that normally lives in the respiratory tract of most people, but causes pneumonia in those with dysfunctional immune systems.
Key terms:
alveoli: terminal branchings of the respiratory tree that act as the primary sites of gas exchange in the lungs
immunosuppression: reducing the activity or efficiency of the immune system
Causes and Symptoms
Pneumocystis jirovecii, a single-celled fungus, commonly lives in the respiratory tracts of healthy people without causing any harm. However, in people whose immune systems do not work properly, P. jirovecii can cause pneumocystis pneumonia (PCP). During World War II, premature and severely malnourished infants were diagnosed with PCP. Later, other cases were observed in immunosuppressed patients: cancer patients receiving chemotherapy, and transplant recipients being treated with immunosuppressants. PCP is one of the most common and severe opportunistic infections in patients with human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS); according to the AIDS InfoNet in 2014, more than 85 percent of people with HIV would end up with PCP without therapy. In 2014 the Centers for Disease Control and Prevention (CDC) estimated that the incidence of PCP among US patients hospitalized with HIV/AIDs was 9 percent. According to the CDC, the mortality rate for immunocompromised patients who have PCP but do not receive treatment is close to 100 percent; with treatment, the mortality rate ranges from 5 percent to 40 percent.
The life cycle of P. jirovecii consists of three different stages: the trophozoite or trophic stage, the sporozoite or precystic form, and the cyst, which contains several spores. Trophozoites live within the alveoli of the lung and are probably the infective form, and transmission occurs by means of airborne transmission.
The symptoms of PCP include shortness of breath upon exertion (dyspnea), fever, nonproductive cough, weight loss, chills, and, rarely, coughing up blood (hemoptysis). PCP patients also have an abnormally fast heart rate (tachycardia, over 100 beats per minute), rapid breathing (tachypnea, more than 20 breaths per minute), and mild crackles and coarse rattling (rhonchi) when they breathe.
Treatment and Therapy
The nonspecific nature of PCP symptoms necessitates other diagnostic tests to confirm the diagnosis. Observing the organism from respiratory tract fluid by means of various tissue stains provides the most definitive confirmation of PCP. Polymerase chain reaction (PCR) tests have been used successfully as well, but are not yet routinely available. Chest x-rays, computed tomography scans, or Gallium-67 scans can provide evidence that the patient has PCP, but are not conclusive.
Even though P. jirovecii is a yeast-like fungus, it does not respond to antifungals, with the possible exception of echinocandin. The first choice for treatment consists of oral or intravenous trimethoprim sulfamethoxazole (TMP-SMX; Septra, Bactrim, Sulfatrim). Patients with sulfa allergies or who have PCP infections that are resistant to TMP-SMX should be given a combination of clindamycin and primaquine or intravenous pentamidine. Patients with severe inflammation and fluid in their lungs are treated with corticosteroids to clear their lungs so that they can breathe.
To prevent PCP (chemoprophylaxis), patients usually take TMP-SMX, or dapsone, dapsone plus pyrimethamine, atovaquone, or aerosolized pentamidine. Smoking cessation can also decrease the rate of recurrent PCP infections.
HIV/AIDS patients who show the symptoms of PCP begin treatment immediately before completion of diagnostic tests. Babies born to mothers infected with HIV begin preventative treatment 4–6 weeks after birth.
Bibliography
“Fact Sheet 515: Pneumocystis Pneumonia (PCP).” AIDS InfoNet. New Mexico AIDS Education and Training Center, U of New Mexico Health Sciences Center, Intl. Assoc. of Providers of AIDS Care, 16 Apr. 2014. Web. 19 Mar. 2015.
“Fungal Diseases: Pneumocystis Pneumonia.” Centers for Disease Control and Prevention. CDC, 13 Feb. 2014. Web. 19 Mar. 2015.
Gallant, Joel E. Johns Hopkins HIV Guide. Burlington, MA: Jones and Bartlett Learning, 2012.
Miller, Robert F., Laurence Huang, and Peter D. Walzer. “Pneumocystis Pneumonia Associated with Human Immunodeficiency Virus.” Clinics in Chest Medicine 34, no. 2 (June 2013): 229–241.
“Pneumocystis Infections.” MedlinePlus. US Natl. Lib. of Medicine, Natl. Inst. of Health, 10 Feb. 2015. Web. 19 Mar. 2015.