Psittacosis, an Uninvited Guest

Abstract

Psittacosis is a zoonotic disease caused by the bacteria Chlamydia psittaci. It commonly presents with flu-like symptoms and community-acquired pneumonia (CAP). The bacteria is transmitted from birds to humans. The most common bird is parrots. Here, we present a cluster of cases of psittacosis in a family which led to the hospitalization of all the five members of the family. All the five patients presented with fever, weakness, dry cough, and dyspnea on exertion. Chlamydia psittaci immunoglobulin M was detected by indirect immunofluorescence assay. The family had a history of contact with parrots. The patients were treated with doxycycline and recovered without any complications. Psittacosis is an uncommon cause of CAP which can have a wide range of presentations, from being asymptomatic, to flu-like symptoms or to fulminant disease. Elaborate history and a high degree of suspicion are very important to come to the diagnosis. The infection is easily treatable with appropriate antibiotics. Public awareness and education regarding the zoonotic transmission of disease can reduce disease incidence.

INTRODUCTION

Psittacosis is a zoonotic disease transmitted to humans from pet birds such as parrots, parakeets, cockatiels, pigeons, and poultry, like turkeys and ducks.[1]

Human infection occurs when they are exposed to infected birds. People commonly affected are poultry workers, veterinarians, and the owners of pet birds. Infected birds may or may not have any clinical symptoms but can shed the bacteria through respiratory secretions or via droppings. When it gets dried, the infected particles mix with the air and can infect someone through inhalation.[1] Previously, it was thought that human-to-human transmission does not occur.[2] However, now it is found to be more contagious, and there were clusters of reported cases of human-to-human transmission.[3]

In general, psittacosis causes mild illnesses such as fever, headache, malaise, and dry cough. The incubation period is from 5 to 14 days (can last as long as 28 days).[1,2] Avian chlamydiosis presents with loss of appetite, breathing difficulties, inflamed eyes, and diarrhea. Most of the people affected with psittacosis respond to antibiotics and recover without any serious complications.

As symptoms of psittacosis are similar to any other respiratory illness and often indistinguishable from viral, bacterial, mycoplasmal, or other atypical pneumonias,[4] it is not very commonly reported. Hence, history of contact with birds and strong suspicion are very important to diagnose this infection.[5] Direct detection of bacteria is not always available.

CASE REPORT

Two patients (mother and daughter aged 45 and 23 years, respectively) were admitted to our hospital with complaints of fever, headache, severe weakness, and dry cough for the past 10 days and dyspnea on exertion for the last 3 days. In both the cases, episodes of fever started 10 days prior to the admission. Initially, it was low grade in nature and subsided with oral antipyretic drugs. It was accompanied by occasional chills. Maximum temperature ranged between 102°F and 102.5°F. Both the patients suffered from dry cough (with occasional scanty expectoration), headache, and weakness for the same duration. They had experienced dyspnea on exertion with chest pain and several bouts of coughing 3 days prior to admission, which was progressive in nature. There was one episode of fainting in case of the daughter. There was no documented history of recent travel. The history was unremarkable excepting for the purchase of two parrots from a local pet market. One parrot died after 5 days of purchase and another died 5 days after the death of the first parrot.

Further detailed history revealed that the remaining three members (50/M, 20/F, and 13/M) of the family also had similar symptoms and were admitted to another hospital. The clue to the case was a history of contact with parrots, which died within a fortnight of purchase.

Table 1 summarizes the demographic details, signs and symptoms, and laboratory and radiological findings (Figure 1b- demonstrates Chest X-ray findings of Case-1) of both the patients.

Table 1.

Clinical and laboratory parameters of both patients

Parameters		Case-1		Case-2
Age/Sex		23/female		45/female
Duration of fever		10 days		10 days
Tmax		102.5°F		102°F
Heart rate		118/min		100/min
Respiratory rate		24/min		28/min
BP		60/90 mmHg		130/80 mmHg
SpO2		94%		95%
Chest auscultation		Bilateral diminished vesicular breath sound with left basal crepitations.		Bilateral diminished vesicular breath sound with right sided crepitations.
Chest X-ray		left lower lobe and right upper zone pneumonia		Bilateral patchy pneumonia
HRCT thorax		bilateral multifocal consolidation with mild right pleural effusion		Bilateral patchy opacity with mild bilateral pleural effusion.
Hb%		9.8g/dl		11.1g/dl
WBC		5000		7400 cu/mm
Neutrophil/ Lymphocytes		60/32%		72/21%
Platelet		1.87 lacs/cumm		4.81 lacs/cumm
C- Reactive protein		2.1 mg/dl		7.1 mg/dl
SGOT & SGPT		46 & 66		120 & 102
Urea & Creatinine		15 & 0.7 mg/dl		16 & 0.6 mg/dl
Procalcitonin		0.53 ng/ml		-

BP: Blood pressure, Hb: Hemoglobin, SGOT: Serum glutamic-oxaloacetic transaminase, SGPT: Serum glutamic pyruvic transaminase, WBC: White blood cell, HRCT: High-resolution computed tomography

Figure 1.

(a) Chlamydial inclusion bodies with the indirect immunofluorescence test, (b) Chest X-ray of a 23-year-old female showed left lower lobe and right upper zone pneumonia

Blood culture, sputum culture and AFB stain, other atypical organisms for pneumonia from the throat and nasopharyngeal swab done by a comprehensive respiratory panel, a multiplex polymerase chain reaction (PCR) (Biofire, FilmArray Respiratory Panel 2 (RP2) version 1.7, Biomerieux) was found negative.

Initially, both the patients were admitted to some other hospital for primary management, but later, they were shifted to our hospital for further management. Both of them were managed with moist oxygen and, initially, empirical antibacterial piperacillin/tazobactam against probable bacterial infection and oseltamivir to cover for influenza infection. Pneumobact panel immunoglobulin M (IgM) (indirect immunofluorescence assay by Vircell) was performed, and Chlamydophila psittaci infection was detected (IgM antibody titer1:20 dilutions) [Figure 1a]. After getting this report, the antibiotic and antiviral were stopped and doxycycline (100 mg) twice daily was started. The patients gradually responded to treatment, and fever subsided after 4 days of admission. Their clinical and hemodynamic parameters stabilized. They were discharged on day 7 of admission with doxycycline for 10 more days (a total of 14 days of therapy). After 2 weeks of follow-up visit, they were found to be fine with radiological clearance.

DISCUSSION

Chlamydophila psittaci is quite an uncommon but not unknown cause of community-acquired pneumonia (CAP) in this part of the country. In general, psittacosis causes mild illness such as fever, headache, malaise, and dry cough. Most of the people recover without any serious complications and with proper treatment. Patients with pneumonia are often diagnosed by chest X-ray or computed tomography scan. Radiological findings of psittacosis usually vary from lobar or interstitial infiltrates with or without atelectasis and homogeneous ground glass appearance. Here, in both the patients, there was mild pleural effusion, which is an uncommon feature in psittacosis, and indeed, there are suggestions that it is rare enough to reconsider the diagnosis.

It is a challenge to identify the causative organism for such an atypical zoonotic origin pneumonia because of its complex biology and intracellular habitat. It is difficult to diagnose as it cannot be isolated in conventional culture and needs cell culture for its isolation. There are few stains such as methylene blue, Giemsa, modified Gimenez, and indirect immunofluorescence, which can identify the elementary bodies of Chlamydophila psittaci, but none of these can specifically identify this bacteria. That is why it is believed that this disease is grossly underdiagnosed and hence underreported. Indirect immunofluorescent assay (microimmunofluorescence “MIF”) kits to detect Chlamydophila psittaci IgM antibodies in human serum or plasma is a reliable method. It is the gold standard serological test to diagnose psittacosis.[6] A titer of antibody above 1:16 is considered significant evidence of psittacosis.[2] Organism isolation from the cell culture is difficult as it is labor intensive, time-consuming, and potentially hazardous. Identification of these bacteria by nucleic acid amplification tests is highly recommended as it gives a sensitive and specific diagnosis. A combination of PCR and serological tests is key to the diagnosis of chlamydiosis.[7] The limitation with PCR is that it is not widely available and the cost of this diagnostic modality is very high.

There are a number of world reports of this zoonotic disease among bird dealers, poultry workers, laboratory persons, and veterinary workers from around the globe. The outbreaks are sporadic. Five European countries have reported an unexpected rise in a number of psittacosis cases in the late part of 2023 and the beginning of 2024. It led to the death of five people. In an outbreak notice, the WHO has mentioned that there were reporting of such cases from various European countries like Austria, Denmark, Germany, Sweden, and The Netherlands. In most of the cases, people had a contact history with wild and domestic birds. Austria reported 14 cases, and Denmark reported a sharp increase in 23 cases; among them, four were fatal from late 2023 through mid-January 2024. Germany reported a spurt of five cases in December 2023, a total of 14 cases in 2023. The Netherlands has reported increased cases since late December, with 21 cases reported. All patients were hospitalized, and one died. Sweden reported 26 cases from November to December 2023. Some of the reported cases developed pneumonia and resulted in hospitalization.[8] Argentina also reported an outbreak of psittacosis, which was first reported on April 17, 2024, in ProMED. There were around 60 cases of psittacosis, which presented with atypical pneumonia, and among them, 20 were confirmed positive by laboratory testing. Many of the affected patients have no history of contact with birds.[9] Wu et al. from China reported a cluster of 4 cases of Chlamydia psittaci pneumonia, of whom three were of the same family and the fourth person was from whom the bird (duck) was purchased. In 2021, during the COVID-19 pandemic, China reported a family outbreak of human psittacosis Li et al. from China reported a family outbreak of human psittacosis in the year 2021 during the COVID 19 pandemic, followed by two additional reports of the whole family being affected by psittacosis was reported by Xiao et al., 2022 and Jing et al., 2023.[10] However, in India, most of the cases were solitary; outbreaks or clusters of cases have almost never been reported. This is probably the first cluster of psittacosis cases that is being reported.

The prognosis depends on the severity of disease, the presence of any comorbidities, and the time of starting specific antibiotics. In a meta-analysis, it is shown that a 1% incidence of CAP is caused by Chlamydophila psittaci.[11] The fatality rate is up to 10% if not treated with appropriate antibiotics.[2] A 94.23% cure rate has been observed if proper antibiotic is administered timely.[12]

Tetracyclines are the drug of choice for psittacosis, but it is contraindicated in children <8 years. Macrolides are the drug of choice for children. Patients with severe presentation should be treated with doxycycline. Beta-lactam antibiotics are ineffective in the treatment of psittacosis.[1]

As psittacosis is difficult to diagnose, a high degree of suspicion for psittacosis and proper history taking help in the early diagnosis of this entity. Proper antibiotic therapy reduces morbidity associated with this condition greatly.[13]

CONCLUSIONS

Psittacosis is a comparatively rare cause of CAP in our country, with a vast range of clinical manifestations varying from being asymptomatic to fulminant disease. This infection is curable with appropriate antibiotics. A vivid and lucid case history, along with high degree of suspicion, is very important. Public awareness and education regarding the zoonotic transmission of disease can reduce disease incidence.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Research quality and ethics statement

The authors followed applicable EQUATOR Network guidelines (http://www.equator-network.org/), notably the CARE guideline, during the conduct of this report.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.