What is it?
Pneumocystosis is a rare disease defined by a fungus infection: Pneumocystis jiroveci. This fungus has infectivity in immunocompromised people whose CD4 count is less than 200 / mm3 of blood. These CD4s are proteins found on the surface of white blood cells, cells of the immune system.
Pneumocystis jiroveci infection is said to be opportunistic. Either the fungus only grows under favorable conditions. In this sense, immunocompromised individuals are more concerned with the disease.
Contamination by this infectious agent is essentially airborne. Once inhaled, it usually infects the lungs. Nevertheless, extra-pulmonary infections have been identified in patients with AIDS (Acquired Immunodeficiency Syndrome).
The symptoms generally associated with this pathology are therefore pulmonary and respiratory: cough respiratory genes (dyspnea) and often added a fever that appears some time later. Pneumocystosis can be lethal in the sense that it is not treated quickly and in the absence of adequate treatment.
Pneumocystosis is a disease caused by a microscopic fungus: Pneumocystis jirovecii.
The latter is part of Ascomycetes (family of fungi) and is responsible for severe pneumonia in immunocompromised patients, especially in individuals infected with HIV (Human Immunodeficiency Virus) and developing AIDS.
To date, this pathogen is difficult to highlight, indeed, it turns out to be non-cultivable in the laboratory.
In addition, thanks to the development of anti-retroviral drugs used in the treatment of AIDS, Pneumocystis jiroveci infection has become “exceptional” in subjects previously infected with HIV.
However, scientists have observed an increase in its incidence in other forms of immunosuppression. These other forms, however, have atypical clinical manifestations and the diagnosis is more difficult to achieve.
Symptoms of Pneumocystis
It is possible to define different symptoms associated with people with AIDS who are infected with P. jirovecii and immunocompromised but uninfected persons.
Concerning the subjects affected by HIV, two forms are observable:
- The pulmonary form: this corresponds to a progression in the associated symptoms. These clinical manifestations correspond to fever, dry coughs and dyspnea (breathing difficulties);
- The extra-pulmonary form is the result of a spread of the pathogen through the blood reaching organs and tissues other than the lungs. This extra-pulmonary form particularly affects the spleen but can also have significant consequences on the liver, the bone marrow, the pleura (membrane covering the lungs), the ganglia, the thyroid, the mastoid (postero-inferior part of the temporal lobe), the auditory canal, the retina, etc.). In addition, pseudo-tumoral digestive forms have been demonstrated in some cases of the disease. It is remarkable that the pulmonary forms of the disease are rarely associated with pulmonary forms.
For people who are immunocompromised but not affected by AIDS, they may also have atypical symptoms of the disease. These cases correspond to subjects who have undergone organ transplants with a rejection of this new organ that requires an increase in the dose of immunosuppressants. Also people with hematological diseases (leukemia, lymphoma, etc.), having undergone hematopoietic stem cell transplants, suffering from collagenosis (Wegener’s disease, periarthritis nodosa, lupus, etc.). Individuals undergoing chemotherapy may also be impacted by the development of pneumocystosis.
The symptoms associated with these cases of immunodeficiency are similar to those characteristic of HIV-related immunodeficiency, but with a more abrupt symptomatic onset and symptom progression is usually rapid.
The origins of the disease
The origin of pneumocystosis is an infection with a fungus: Pneumocystis jiroveci. This mushroom is cosmopolitan, found around the world and very ubiquitous (everywhere in the environment). Moreover, its development is opportunistic, that is to say that it is able to develop only under certain conditions. These favorable conditions of development concern particularly the immuno-depressed persons.
The development cycle of this parasite is currently not fully known. Infection is by air (inhalation). The infective form of the fungus has not yet been demonstrated; moreover, other more well-known forms have been found within the pulmonary alveoli in mammals. Beyond the lungs, this fungus has also been demonstrated through other organs: spleen, liver, heart, lymph nodes, bone marrow.
In the organs, the infectious agent forms mature cysts that release intracystic bodies. These intracystic bodies are then transformed rapidly into trophozoite (the vegetative form of the infectious agent). The trophozoite form has only one nucleus and has filopods (morphological features visible under the microscope). These morphological characteristics allow the fungus to dock with the epithelial cells of the body (cells forming the superficial layer of the skin). At the level of these epithelial cells, the fungus is able to develop rapidly.
Subsequently, pre-cysts, which after a short mononuclear stage become multinucleated.
Pneumocystis jiroveci infection is usually by an external source. Nevertheless, no environmental reservoir has yet been identified. Human-to-human transmission is also possible in the case where the infection concerns a group of people within a group (pediatric, hematology, oncology, resuscitation, etc.). This human-to-human contamination is done by air.
Risk factors for Pneumocystis
The risk factors for developing pneumocystosis are:
– a deficient immune system: immunodeficiency, caused by a primary infection with HIV (Acquired Immune Deficiency Virus);
– immunodeficiency caused by other factors: organ rejection after transplantation, chemotherapy, etc.;
– the presence of several infected persons in a care unit (oncology, hematology, etc.).
Prevention and treatment of Pneumocystis
The diagnosis of pneumocystosis is usually made through a bronchio-alveolar lavage.
In addition, different diagnostic methods exist depending on the form of the disease:
– For the pulmonary form, an auscultation of the patient allows first of all to detect a possible respiratory deficiency. In addition, chest x-ray and lung CT are needed to confirm the diagnosis. An aspect of the lungs in “frosted glass” during the realization of medical imaging is characteristic of the pathology. A blood test can also raise suspicion about the possible presence of this form through the presence of hypoxia. In the case of late diagnosis, the chest X-ray shows opacity of the lungs or “white lungs”. In this context, the subject’s prognosis is uncertain;
– For the extra-pulmonary form, the diagnosis is more complicated. Previously the use of pentamidine aerosols was recommended for patients with this form of the disease; however it is no longer relevant today.
Diagnosis through the use of molecular biology is also possible through PCR (Polymerase Chain Reaction). Nevertheless, this genomic amplification technique does not always make it possible to differentiate the healthy carriers from the sick carriers.
The cure for pneumocystosis is made with 2 drugs:
– cotrimoxazole as first intention;
– isethionate when the patient is intolerant to the first.
Side effects are widely observed in nearly half of patients. These adverse effects include: rash, fever, development of leukopenia (abnormally low levels of white blood cells, white blood cells), anemia (abnormally low levels of iron in red blood cells), thrombocytopenia (abnormally low levels number of circulating platelets), elevation of transaminases (enzymes present in many organs), etc.