Pneumocystosis is a rare disease defined by infection with a fungus: Pneumocystis jiroveci. This fungus has an infectious power 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. (5)

Infection with Pneumocystis jiroveci is said to be opportunistic. Either, the fungus only develops under conditions which are favorable to it. In this sense, immunocompromised subjects are more affected by the disease.

Contamination by this infectious agent is essentially aerial. When inhaled, it usually infects the lungs. Nevertheless, extra-pulmonary contaminations 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 to a fever which appears some time later. Pneumocystosis can be lethal in the sense that it is not taken care of quickly and in the absence of adequate treatment. (1)

Pneumocystosis is a disease caused by a microscopic fungus: Pneumocystis jirovecii.

The latter is part of the Ascomycetes (family of fungi) and is responsible for severe pneumopathies in immunocompromised patients, especially in individuals infected with HIV (Human Immunodeficiency Virus) and developing AIDS. (3)

To date, this pathogen is difficult to demonstrate, in fact, it turns out to be non-cultivable in the laboratory.

Moreover, thanks to the development of anti-retroviral drugs used in the treatment of AIDS, infection with Pneumocystis jiroveci became “exceptional” in subjects previously infected with HIV.

However, scientists have observed an increase in its incidence in other forms of immunosuppression. However, these other forms present atypical clinical manifestations and the diagnosis is more difficult to achieve. (4)

It is possible to define different symptoms associated with people with AIDS and infected with P.jirovecii and people who are immunocompromised but not infected.

 Regarding subjects affected by HIV, two forms can be observed: (5)

• the pulmonary form: this corresponds to a progression in the associated symptoms. These clinical manifestations correspond to fever, dry coughs and dyspnea (difficulty breathing);
• the extra-pulmonary form results from the spread of the pathogen through the bloodstream reaching organs and tissues other than the lungs. This extra-pulmonary form particularly impacts the spleen but can also have significant consequences on the liver, bone marrow, pleura (membrane covering the lungs), lymph nodes, thyroid, mastoid (postero-inferior part of the temporal lobe ), ear canal, retina, etc.). In addition, digestive pseudo-tumor forms have been demonstrated in certain cases of the disease. It is remarkable that the pulmonary forms of the disease are rarely associated with the pulmonary forms.

For people who are immunocompromised but not affected by AIDS, they may also present with atypical symptoms of the disease. These cases correspond to subjects who have undergone organ transplants with a rejection of this new organ which requires an increase in the dose of immunosuppressants. Also people with hemopathies (leukemia, lymphomas, etc.), having undergone hematopoietic stem cell transplants, suffering from collagenosis (Wegener’s disease, periarthritis nodosa, lupus, etc.). Individuals undergoing chemotherapy can also be impacted by the development of pneumocystosis.

Symptoms associated with these cases of immunodeficiency are similar to those characteristic of HIV-related immunodeficiency but with a more abrupt onset of symptoms and symptom progression is generally rapid. (5)

The origin of pneumocystosis is an infection with a fungus: Pneumocystis jiroveci. This fungus is cosmopolitan, is found all over the world and very ubiquitous (everywhere in the environment). In addition, its development is opportunistic, that is to say that it is able to develop only under certain conditions. These favorable conditions for development particularly concern immunosuppressed people.

The development cycle of this parasite is currently not fully understood. Infection occurs through the air (inhalation). The infectious form of the fungus has not yet been demonstrated, moreover, other more well-known forms have been observed in the pulmonary alveoli in mammals. Beyond the lungs, this fungus has also been demonstrated through other organs: the spleen, liver, heart, lymph nodes, bone marrow. (5)

At the organ level, the infectious agent forms mature cysts which release intracystic bodies. These intracystic bodies then transform rapidly into trophozoite (vegetative form of the infectious agent). The trophozoite form has a single nucleus and has filopodia (morphological characteristics visible under a microscope). These morphological characteristics allow the fungus to attach to the body’s epithelial cells (cells forming the surface layer of the skin). At the level of these epithelial cells, the fungus is able to develop rapidly.

Then, pre-cysts are formed which, after a short mononuclear stage, become multinucleated.

Infection with Pneumocystis jiroveci is usually done by an outside source. However, no environmental reservoir has yet been identified. Human-to-human transmission is also possible in the case where the infection concerns a set of people within a group (pediatric, hematology, oncology, resuscitation services, etc.). This human-to-human contamination occurs by air. (5)

The risk factors for developing pneumocystosis are:

– a deficient immune system: immunodeficiency, caused by a primary infection with HIV (Acquired Immunodeficiency Virus);

– immunodeficiency caused by other factors: organ rejection after transplantation, chemotherapy, etc. ;

– the presence of several infected people in a care service (oncology, hematology, etc.).

The diagnosis of pneumocystosis is generally made through bronchio-alveolar lavage. (1)

In addition, different diagnostic methods exist depending on the form of the disease: (5)

– for the pulmonary form, auscultation of the patient first of all makes it possible to detect a possible respiratory deficiency. In addition, a chest x-ray and a scan of the lungs are needed to confirm the diagnosis. A “ground glass” appearance of the lungs when performing medical imaging is characteristic of the pathology. A blood test also allows suspicion as to the possible presence of this form through the presence of hypoxia. In the event that the diagnosis is late, the chest x-ray shows an opacity of the lungs or also called “white lungs”. In this context, the subject’s vital 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 by the use of molecular biology is also possible through PCR (Polymerase Chain Reaction). However, this genomic amplification technique does not always make it possible to differentiate healthy carriers from sick carriers.

The curative treatment of pneumocystosis is done with 2 drugs:

– first-line cotrimoxazole;

– isethionate when the patient is intolerant to the first.

Side effects are widely observed in almost half of patients. These adverse effects include: skin rashes, fever, development of leukopenia (abnormally low level of leukocytes, white blood cells), anemia (abnormally low level of iron in red blood cells), thrombocytopenia (abnormally low level the number of circulating platelets), an increase in transaminases (enzymes present in many organs), etc.