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Pneumocystosis, Pneumocystis Pneumonia (Fungal Lung Infection Caused by the Fungus Pneumocystis Jiroveci) in Dogs

Occurrence: rarer
Location of illness: Chest

Author: Dr. med. vet. Gisa Löwe | Last modified: 06.11.2025

Pneumocystosis, also known as Pneumocystis Pneumonia, is a rare but serious fungal infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. of the lungs in dogs, caused by the fungus Pneumocystis jiroveci. This infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. primarily affects immunocompromised dogs and can lead to severe respiratoryRespiratory refers to breathing or the process of breathing. Respiratory diseases affect the respiratory tract and can impair the ability to breathe effectively. diseases.

The most important facts at a glance

Pneumocystis Pneumonia is a lung infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. in dogs caused by the opportunistic fungus Pneumocystis jiroveci. This fungus is common in the environment and is normally kept in check by the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. of healthy dogs. The disease mainly occurs in dogs with a weakened immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body., which can be caused by genetic predispositions, diseases, or immunosuppressiveImmunosuppressive agents are medications or substances that specifically suppress the activity of the immune system. They are used in dogs and cats to treat autoimmune diseases, allergies, and to prevent rejection reactions after transplants. medications. Certain breeds such as the Cavalier King Charles Spaniel and the Dachshund are particularly at risk.

The infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. occurs through the inhalationInhalation is the act of breathing air or other substances into the lungs through the nose or mouth. In dogs and cats, inhalation of toxins, smoke, or allergens can lead to respiratory problems. of fungal spores, which settle in the lungs and can cause symptoms such as Cough, RespiratoryRespiratory refers to breathing or the process of breathing. Respiratory diseases affect the respiratory tract and can impair the ability to breathe effectively. distress, and Fever. DiagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. requires specialized tests such as X-rays and bronchoalveolar lavageBronchoalveolar lavage is a medical procedure in which a portion of the lung is rinsed with a small amount of sterile fluid to collect cells and other components for diagnostic purposes. It is often used to make a diagnosis of lung diseases., supplemented by PCR tests to identify the fungus. AntimicrobialAn antimicrobial substance is an agent that serves to inhibit the growth of microorganisms such as bacteria, viruses, fungi, and protozoa, or to kill them. Antimicrobials are frequently used to treat infections. drugs such as trimethoprim-sulfamethoxazole are used for treatment, and in severe cases, oxygen therapyTherapy refers to the treatment of diseases or disorders with the aim of alleviating symptoms, promoting healing, or improving quality of life. Therapies can be medicinal, surgical, or through other medical interventions. may be necessary. TherapyTherapy refers to the treatment of diseases or disorders with the aim of alleviating symptoms, promoting healing, or improving quality of life. Therapies can be medicinal, surgical, or through other medical interventions. often lasts several weeks to months, and early diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. significantly improves the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop..

Preventive measures focus on strengthening the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. through a balanced diet and regular veterinary check-ups. Research focuses on the development of better diagnostic and treatment methods, strengthening the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body., and understanding the epidemiology of the disease. Despite advances in research, challenges remain, particularly in the development of more effective diagnoses and treatments to improve the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. of affected dogs.

Causes

Pneumocystis jiroveci is an opportunistic fungus that is found in many environments and can often be present in healthy dogs without symptoms. Normally, a healthy dog’s immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. can handle the fungus without causing illness.

The infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. usually occurs in dogs that have a weakened immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body.. This can be caused by genetic predispositions, as in some breeds, or by diseases and medications that suppress the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body.. Certain breeds such as the Cavalier King Charles Spaniel and the Dachshund have a higher risk of developing this infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease., which is attributed to genetic factors.

Transmission usually occurs through inhalationInhalation is the act of breathing air or other substances into the lungs through the nose or mouth. In dogs and cats, inhalation of toxins, smoke, or allergens can lead to respiratory problems. of spores of the fungus. Under normal circumstances, the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. can eliminate these spores without problems. In immunocompromised dogs, however, the spores can settle and multiply in the alveoli, leading to inflammation and thus to the symptoms of Pneumocystis Pneumonia.

Symptoms

Very common symptoms:

Common symptoms:

Rare symptoms:

Muscle Atrophy

The symptoms of Pneumocystis Pneumonia in dogs are often non-specific and can mimic other respiratoryRespiratory refers to breathing or the process of breathing. Respiratory diseases affect the respiratory tract and can impair the ability to breathe effectively. diseases. They usually include chronicChronic refers to a condition or disease that is long-lasting or permanent. Chronic diseases often develop slowly and can lead to persistent or recurring health problems over time. cough, DyspneaDyspnea, also known as shortness of breath, is the subjective feeling of breathlessness or difficulty breathing. It can be a symptom of a variety of conditions, including heart disease, lung disease, and anemia. (labored breathing), rapid breathing (tachypneaTachypnea or tachypoe refers to an increased respiratory rate that is above the normal range for the respective living being. It may be a sign of shortness of breath or other respiratory diseases.), and sometimes Fever. In severe cases, affected dogs may also show signs of Lethargy, loss of appetite, and Weight loss.

A characteristic feature of this infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. is the progressiveProgressive describes a condition or disease that worsens over time. This term is often used to characterize the course of an illness that causes increasingly severe symptoms or damage. worsening of respiratoryRespiratory refers to breathing or the process of breathing. Respiratory diseases affect the respiratory tract and can impair the ability to breathe effectively. symptoms that do not improve despite conventional antibiotic treatment. Cough may initially be mild but often worsens over time. DyspneaDyspnea, also known as shortness of breath, is the subjective feeling of breathlessness or difficulty breathing. It can be a symptom of a variety of conditions, including heart disease, lung disease, and anemia. (labored breathing) often occurs with minimal exertion or even at rest.

Diagnosis

The diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. of Pneumocystis Pneumonia requires a thorough clinical examination and specialized diagnostic tests. Often, a chest X-rayX-ray is an imaging technique that uses X-rays to create images of the inside of the body. It is often used to diagnose bone fractures, lung diseases, and other conditions. is taken to detect signs of Pneumonia. Typical X-ray findings may reveal diffuse interstitial patterns, indicating a general inflammation of the lung tissues.

To confirm the diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients., a bronchoalveolar lavageBronchoalveolar lavage is a medical procedure in which a portion of the lung is rinsed with a small amount of sterile fluid to collect cells and other components for diagnostic purposes. It is often used to make a diagnosis of lung diseases. (BAL) can be performed, in which a fluid sample is taken from the airways and analyzed in the laboratory. The identification of Pneumocystis jiroveci in these samples is crucial for the diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients..

In addition, PCR tests (polymerase chain reaction) can be used to detect the genetic material of the fungus. These tests are very sensitive and specific, making them a valuable tool in the diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. of Pneumocystis Pneumonia.

Therapy

Treatment of Pneumocystis Pneumonia usually requires a combination of antimicrobialAn antimicrobial substance is an agent that serves to inhibit the growth of microorganisms such as bacteria, viruses, fungi, and protozoa, or to kill them. Antimicrobials are frequently used to treat infections. drugs that are specifically effective against Pneumocystis jiroveci. Trimethoprim-sulfamethoxazole is often the drug of choice, as it has proven effective in treating this infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease..

In severe cases, additional oxygen therapyTherapy refers to the treatment of diseases or disorders with the aim of alleviating symptoms, promoting healing, or improving quality of life. Therapies can be medicinal, surgical, or through other medical interventions. may be required to support the dog’s breathing. If the dog’s immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. is weakened due to an underlying disease or medication, an adjustment to the treatment of that condition may be necessary.

Treatment can take several weeks to months, depending on the severity of the infection and the dog’s response to therapyTherapy refers to the treatment of diseases or disorders with the aim of alleviating symptoms, promoting healing, or improving quality of life. Therapies can be medicinal, surgical, or through other medical interventions.. It is important that treatment is not stopped too early, as this could lead to a relapse of the infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease..

Prognosis and follow-up care

The prognosis for dogs with Pneumocystis Pneumonia varies and depends heavily on the speed of diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients., the severity of the infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease., and the dog’s general health. Dogs that are diagnosed and treated early have a better prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop..

However, treatment can be lengthy, and in some cases, the infection may progress despite therapy. In dogs with severe symptoms or those whose immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. is severely weakened, the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. may be more guarded.

A full recovery is possible, but regular veterinary follow-ups are important to monitor the progress of treatment and to detect possible relapses early.

Prevention

Since Pneumocystis Pneumonia mainly affects immunocompromised dogs, preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. is largely aimed at strengthening and supporting the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body.. A balanced diet, regular veterinary check-ups, and avoiding stressStress refers to the state of an organism reacting to external stimuli or demands. In veterinary medicine, stress can have physical or psychological effects on animals, impacting their health and well-being. are basic measures that can strengthen the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body..

For dogs that need to take immunosuppressiveImmunosuppressive agents are medications or substances that specifically suppress the activity of the immune system. They are used in dogs and cats to treat autoimmune diseases, allergies, and to prevent rejection reactions after transplants. medications, it is important to dose these medications in such a way that the suppression of the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. is minimized without endangering the underlying disease. Regular blood tests can help monitor the immune status and make adjustments to the medication.

There are currently no specific vaccinations against Pneumocystis jiroveci, so exposureExposure refers to the Contact with or subjection to certain substances, environmental factors, or pathogens. In veterinary medicine, this can include Contact with toxins, allergens, or infectious agents that can cause health problems in dogs and cats. to potential sources of infection should be avoided as much as possible. This can be achieved by minimizing contact with infected animals and avoiding environments with high spore loads.

Outlook on current research

Pneumocystis Pneumonia (PCP) in dogs is a relatively rare but serious disease caused by the fungus Pneumocystis jiroveci. This fungus is widespread in the environment and can lead to severe lung infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. in immunocompromised dogs. Research on PCP in dogs is currently focused on better diagnostics, treatment options, and understanding the epidemiology of the disease.

A significant advance in diagnostics is the use of polymerase chain reaction (PCR) tests, which allow veterinarians to identify the fungus more quickly and accurately. Traditionally, the diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. was made by examining lung tissue samples, which is invasiveInvasive describes medical procedures or pathogens that enter the body or penetrate tissue. In medicine, invasive procedures can range from minimally invasive techniques to open surgery. and often risky for the patient. PCR tests offer a less invasiveInvasive describes medical procedures or pathogens that enter the body or penetrate tissue. In medicine, invasive procedures can range from minimally invasive techniques to open surgery. method to determine the presence of Pneumocystis jiroveci, thus improving the chances of early treatment.

Regarding treatment, there is ongoing research into the effectiveness of various antifungals. So far, trimethoprim-sulfamethoxazole (TMP-SMX) and pentamidine are the main drugs used to treat PCP in dogs. However, scientists are also investigating alternative treatment options, as some dogs may develop resistanceResistance refers to the ability of microorganisms to withstand the effects of antibiotics, antifungals, or other antimicrobial drugs. Resistance can also refer to the body's ability to be insensitive to diseases or toxins. to these drugs or are unable to tolerate them due to side effects.

Furthermore, the role of the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. is being intensively researched. Dogs that develop PCP often have a weakened immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body., whether due to genetic factors, other diseases, or the use of immunosuppressiveImmunosuppressive agents are medications or substances that specifically suppress the activity of the immune system. They are used in dogs and cats to treat autoimmune diseases, allergies, and to prevent rejection reactions after transplants. drugs. Research is focused on how the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. of dogs can be strengthened to minimize the risk of infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease. and support recovery.

Another area of research is the epidemiology of the disease. Studies are being conducted to determine which dog breeds and age groups are most commonly affected and which environmental factors increase the risk of infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease.. This information is crucial for developing preventive measures and controlling the spread of the disease.

In summary, while research on Pneumocystis Pneumonia in dogs is making progress, many challenges remain. The development of more effective diagnostic and treatment methods remains a central goal to improve the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. for affected dogs.

Frequently asked questions (FAQs)

What is Pneumocystis Pneumonia in dogs? Pneumocystis Pneumonia is a lung infection caused by the fungus Pneumocystis jiroveci. It mainly occurs in dogs with a weakened immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. and can lead to severe respiratoryRespiratory refers to breathing or the process of breathing. Respiratory diseases affect the respiratory tract and can impair the ability to breathe effectively. problems.
What symptoms do dogs with PCP show? The most common symptoms include Cough, Dyspnea (labored breathing), rapid breathing, Fever, and general weakness. Affected dogs may also show Weight loss and loss of appetite.
How is PCP diagnosed in dogs? The diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. is often made through a combination of clinical symptoms, X-rays of the lungs, and special tests such as PCR to identify the fungus. Sometimes lung tissue samples are also necessary.
Can PCP be cured? Yes, with the right treatment, PCP can be treated successfully. However, the prognosisThe prognosis is the prediction of the likely course and outcome of a disease based on the general state of health, the nature of the disease, and the response to treatment. It can provide information on how a disease is expected to develop. depends heavily on the dog’s health and the speed of diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and treatment.
Which dogs are most at risk of developing PCP? Dogs with weakened immune systems are most at risk. These include dogs with genetic immune defects, those taking immunosuppressiveImmunosuppressive agents are medications or substances that specifically suppress the activity of the immune system. They are used in dogs and cats to treat autoimmune diseases, allergies, and to prevent rejection reactions after transplants. medications, and dogs with other serious diseases.
How is PCP treated in dogs? The standard treatment usually includes antifungals such as trimethoprim-sulfamethoxazole (TMP-SMX). In severe cases, other medications and supportive measures such as oxygen therapyTherapy refers to the treatment of diseases or disorders with the aim of alleviating symptoms, promoting healing, or improving quality of life. Therapies can be medicinal, surgical, or through other medical interventions. may also be necessary.
Can PCP be transmitted to humans? No, the fungus Pneumocystis jiroveci, which causes PCP in dogs, is not transmissible to humans. It is a species-specific infectionAn infection is the colonization and multiplication of pathogens such as bacteria, viruses, fungi, or parasites in an organism, which often, but not always, leads to a disease..
Are there preventive measures against PCP? There is no direct preventionPrevention includes measures taken to prevent diseases or injuries. In veterinary medicine, this includes vaccinations, parasite control, and health monitoring. against PCP, but strengthening the immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. and avoiding immunosuppressiveImmunosuppressive agents are medications or substances that specifically suppress the activity of the immune system. They are used in dogs and cats to treat autoimmune diseases, allergies, and to prevent rejection reactions after transplants. medications, if possible, can reduce the risk. Regular veterinary check-ups also help keep your dog’s immune systemThe immune system is the body's defense system against infectious agents such as bacteria, viruses, fungi, and parasites. It comprises a complex network of organs, cells, and molecules that work together to protect the body. healthy.
How long does recovery from PCP take? The recovery time varies depending on the severity of the disease and the individual health of the dog. With timely diagnosisA diagnosis is the identification of a disease or condition by its symptoms and/or results from diagnostic tests. It is the first step in the management and treatment of patients. and treatment, some dogs can recover within weeks, while others require a longer recovery period.
Are certain breeds more susceptible to PCP? Some studies suggest that certain breeds, such as the Cavalier King Charles Spaniel, may be more susceptible to PCP due to genetic predispositions. However, further research is needed to confirm this.