Beware of being "pigeoned"! Beware of the hidden dangers of domestic pigeons!

Author: Ma Ruirui Liu Wenjing Peking Union Medical College Hospital

Reviewer: Xiao Meng, Associate Researcher, Peking Union Medical College Hospital

With the advancement of science and technology and society, people's quality of life is constantly improving, and pets play an increasingly important role in our lives. They are not only good playmates for children, but also bring us unconditional love and companionship. However, did you know that keeping pets also comes with certain health risks. Pets may carry some pathogens, and these microorganisms may have an impact on our health. Even the familiar little pigeons that symbolize peace and friendship are no exception. Pigeons sometimes carry new cryptococci, which are mainly transmitted through the air and may cause infection when inhaled into the human body. Next, we will take you to understand the new cryptococcal infection problems associated with pigeons.

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1. What is Cryptococcus neoformans? Why does it infect humans?

Cryptococcus neoformans is a thick-capsulated, saprophytic yeast, the most important pathogenic fungus in the genus Cryptococcus, and is widely found in the soil in the natural environment, as well as in the feces of birds including pigeons. In particular, pigeon feces often accumulate in pigeon nests, providing a good environment for the growth and reproduction of Cryptococcus neoformans. Therefore, domestic pigeons have become an important potential source of infection with Cryptococcus neoformans in humans.

Cryptococcus neoformans reproduces by blastospores. When we come into contact with pigeon droppings, the spores of Cryptococcus neoformans will be inhaled into the human body through the respiratory tract, and then go down and colonize in the lower respiratory tract of humans. When the human immune function is damaged or reduced, the colonized Cryptococcus neoformans will multiply in large numbers, causing cryptococcal pneumonia; it may also continue to spread from the lungs through the blood, invade the central nervous system through the blood-brain barrier, and form cryptococcal meningitis. In addition, the spread of Cryptococcus neoformans with the blood can also cause infections in other parts of the skin and disseminated cryptococcosis.

2. What harm does infection with Cryptococcus neoformans cause to the human body?

The initial symptoms of Cryptococcus neoformans infection are relatively hidden, with 60% to 80% of patients experiencing headaches and fever, often accompanied by dizziness. Because the symptoms of infection are nonspecific, it is often misdiagnosed as a common cold. However, as the disease progresses, patients will experience more symptoms, and the clinical symptoms vary depending on the site of infection.

The following are the clinical manifestations of the most common sites of infection:

1. Although inhalation is a common route of cryptococcal infection, pulmonary infection can often be hidden without obvious symptoms. The clinical manifestations of pulmonary cryptococcosis are highly heterogeneous, ranging from asymptomatic, mild symptoms to severe respiratory distress syndrome. Common symptoms include cough, sputum, dyspnea, chest pain, hemoptysis, etc. Patients may also experience fever, fatigue, and weight loss.

2. New cryptococcal meningitis is the most common manifestation of cryptococcal disease in the central nervous system. Patients will have gradually worsening severe headaches, nausea and vomiting, positive meningeal irritation signs, impaired consciousness, memory loss, etc. Most patients have severely increased intracranial pressure.

3. Cutaneous cryptococcosis can be divided into primary and secondary, with secondary being the main type. The main difference between the two is whether the first site is the skin or other organs outside the skin. The clinical symptoms of cutaneous cryptococcosis vary, and are commonly manifested as small papules of varying sizes with an umbilicus in the center, large erythema, acne-like rashes, or ulcers formed by necrosis in the middle of the rash. Secondary cutaneous cryptococcosis usually leads to disseminated cryptococcosis.

3. How to determine whether you are infected with Cryptococcus neoformans?

An effective way to determine whether a person is infected with Cryptococcus neoformans is to conduct laboratory tests, that is, ink staining, isolation and culture, or histopathological examination of sputum, cerebrospinal fluid, blood, skin lesions, and tissue or body fluid specimens suspected of being infected with Cryptococcus neoformans. Direct microscopic examination or positive culture of Cryptococcus neoformans in specimens is the basis for the diagnosis of Cryptococcus neoformans. In addition, we can also screen for Cryptococcus neoformans through serological detection of Cryptococcus neoformans capsule antigens or molecular biology methods.

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4. How to prevent the potential pathogenic risks brought by young pigeons?

1. Pigeon breeders should strengthen the hygiene of pigeon nests, clean and disinfect them regularly (once a week), and avoid being overly intimate with pigeons.

2. For some people with underlying diseases and low immunity, such as cancer patients, patients taking immunosuppressants for a long time, etc., they should reduce contact with pigeons and be careful not to go to environments containing pigeon droppings.

3. If pigeon breeders have symptoms such as fever, headache, neck pain, etc., they should go to the hospital specialist for treatment in time. Once diagnosed, antifungal drugs should be taken as prescribed by the doctor. The treatment cycle of new cryptococcal infection is relatively long, and the course of treatment can be more than 10 weeks, mostly 1 to 2 years or even longer. During the treatment period, do not stop the medication without authorization, otherwise it is easy to relapse or other complications, so you must strictly follow the doctor's instructions.

4. Even if you don't raise pigeons, you may still be at risk of infection when passing through squares where pigeons often gather or feeding pigeons in places such as zoos. In addition, some other poultry and birds may also carry new cryptococci, so you also need to be vigilant when in contact with these animals.

References

[1] Chinese Society of Infectious Diseases. Expert consensus on the diagnosis and treatment of cryptococcal meningitis[J]. Chinese Journal of Infectious Diseases, 2018, 36(4):193-199.

[2] Cai Baiqiang, Li Longyun. Peking Union Medical College Respiratory Diseases[M]. Beijing: Peking Union Medical College Press, 2012.

[3]Xu Yingchun. Atlas of Clinical Mycology. Part 3[M]. Beijing: Peking Union Medical College Press, 2022.