The Topic of This Month Vol.23 No.10(No.272)
Psittacosis is a zoonosis caused by Chlamydia psittaci infection. Infection usually occurs when a person inhales the organisms, which have been aerosolized from dried feces or respiratory secretions of infected birds. Other means of exposure include mouth-to-beak contact. In typical cases, after exposure, there is an incubation period of a week or two; high fever suddenly appears accompanying coughing in a high frequency, headaches, and moderate bradycardia and is often followed by liver dysfunction. Some mild cases spontaneously recover with only influenza-like symptom or recover by treatment as atypical pneumonia without diagnosis of psittacosis. Nevertheless, the systemic symptoms of such cases that have developed pneumonia are severer than those of C. pneumoniae -caused pneumonia. In severe pneumonia cases having received inadequate initial treatment, meningitis, multiorgan failure, disseminated intravascular coagulopathy (DIC), and even physical shock may occasionally develop taking a fatal course. In a case of a suspected psittacosis, antibiotic treatment must begin immediately. Tetracyclines are the antibiotics of the first choice, followed by macrolides and fluoroquinolones (but for pregnant women and children, macrolides are the first choice); ƒÀ-lactam antibiotics or aminoglycosides are not effective. For differential diagnosis from pneumonia due to Mycoplasma pneumoniae or C. pneumoniae , it is important to know whether possible contact with birds occurred.
The National Epidemiological Surveillance of Infectious Diseases: Since psittacosis used to be included in atypical pneumonia in the category of diseases to be reported by the sentinel clinics, the actual state was not clarified. After enactment of the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law) in April 1999, it has been listed under the category IV notifiable infectious diseases and all physicians have been obliged to notify the cases. A total of 122 cases have been notified; 23 in 1999 (April - December), 18 in 2000, 36 in 2001, and already over 45 as of August 28, 2002. The increase has largely been due to the outbreaks described below; reports of sporadic cases were also on the increase. As the symptoms reported, atypical pneumonia accompanying respiratory difficulty and severe pneumonia accounted for one third, and other main symptoms were fever, cough, and fatigue. Reported cases by prefecture are shown in Fig. 1. Except for the seven cases in Tokyo in 2001 and 10 in Shimane and eight in Hiroshima prefectures in 2002, no tendency of concentrating cases in a certain area was confirmed. According to the reports in May-June, 1999 through 2001, the bird reproductive season, cases tended to be on the increase (Fig. 2). From the end of 2001 toward 2002, such seasonal variation has become unstable due to the new outbreaks. There are more adult psittacosis cases of different ages with a peak at the 50s (Fig. 3); there were 51 male and 71 female cases. Parakeets have often been the estimated source of infection of psittacosis, accounting for 70% of bird species ascribed.
Outbreaks: In June 2001, five workers assisting a delivery of a Siberian moose at a zoo in Kanagawa Prefecture developed a febrile respiratory disease including a case of pneumonia. Epidemiological investigations and various laboratory examinations were conducted, finding a psittacosis outbreak due to inhalation or per oral infection of C. psittaci being infected on the placenta of a moose (see p. 250 of this issue). Five psittacosis cases were notified in Kanagawa Prefecture in December 2001 (see Fig. 1 and Fig. 2). Thus, it is noteworthy that mammals occasionally transmit C. psittaci to humans.
Psittacosis was confirmed in a total of 17 cases including 12 visitors during November - December 2001 and five workers of a bird park in Shimane Prefecture where about 1,300 birds were being raised. Cases were diagnosed during December 2001-March 2002 (see Fig. 2) and notified in Shimane (10 cases), Hiroshima (four cases), Osaka (two cases), and Tottori Prefectures (one case) (see Fig. 1). No aviary outbreaks had ever occurred in Japan; examination for C. psittaci in the birds, molecular epidemiological investigation of C. psittaci strains (see p. 248 of this issue) and environmental investigation were done. Serological tests of 93 workers have found infection of eight workers, including two cases with influenza-like symptoms and six asymptomatic cases besides notified cases (see p. 247 of this issue).
Problems involved in diagnostic methods: In the National Epidemiological Surveillance of Infectious Diseases, the criteria of notification are (1) Isolation of C. psittaci from sputum, blood, or autopsied specimens of various organs, (2) Detection of C. psittaci gene by PCR or PCR-RFLP, and (3) Detection of serum antibody against C. psittaci : Antibody titers of 1:4 or higher by immunofluorescence (IF). (When purified C. psittaci or C. psittaci -infected cells are used, identification of species is possible). C. psittaci can be isolated from patient's pharyngeal specimens or birds, nevertheless only at limited facilities because cultured cells are necessary and laboratory infection must be prevented. Gene detection by PCR is not so popular as yet. The diagnostic methods used in reported cases are mostly serological diagnosis by complement fixation (CF). Psittacosis CF is a conventional method. However, as Chlamydia -common antigen is used, false positive reaction may occasionally occur due to a previous infection with C. trachomatis or C. pneumoniae , which may cause troubles in diagnosis of C. psittaci infection. For more accurate psittacosis diagnosis and further understanding the actual state, it seems necessary to ask the prefectural and municipal public health institutes (PHIs) or the National Institute of Infectious Diseases (NIID) for confirmatory diagnosis by determining C. psittaci -specific antibody by micro-IF, when CF gives positive results. In the future, development of a simpler and more specific method such as enzyme-linked immunosorbent assay (ELISA) is desired.
Prevention and control: At present, it is presumed that 3 million households raise pet birds in Japan, and 30-50% of healthy (without symptoms) birds possess C. psittaci (Hiyoshi et al., presented at Annual Meeting of the Japanese Society of Veterinary Science, 1994). Such a high carrier rate has been reported also for wild birds (Miyake et al., Kansenshogaku Zassi, 60, 473-477, 1986), nonetheless only few human infections from wild birds have been reported. Although a large number of infected birds are presumably raised, the number of psittacosis case reports is small. Little has been known on the rate of human inapparent infection and the factors required for developing psittacosis, which awaits development of further studies.
There are hundreds of bird and animal parks in Japan. Many of them are providing real opportunities of mutual contact between animals and humans. In Japan, such measures have been taken as "importation tests of psittacine (parrot-type) birds", note by Director, Animal Quarantine Service, the Ministry of Agriculture, Forestry and Fisheries, April 3, 1986, and "the control of psittacosis from birds", note by Head, the Veterinary Sanitation Division, the Environmental Health Bureau, the Ministry of Health and Welfare, October 7, 1987. In response to the above-mentioned outbreak in Shimane Prefecture, the Ministry of Health, Labour, and Welfare issued "The intensive control of psittacosis from birds" to local governments to call their further attention (January 17, 2002, see p. 251 of this issue).
Treatment of diseased birds with antibiotics has been conducted under several treatment protocols (CDC, MMWR Vol. 49, No. RR-8, 2000); elimination of the pathogenic agent by antibiotic administration has been attempted (see p. 249 of this issue). Nevertheless, elimination of C. psittaci from all birds as a control of psittacosis is not realistic.
From now on, establishing adequate hygienic control systems such as quarantine of birds, improvement of methods for raising and displaying birds, and monitoring the health conditions of birds are desired for prevention of psittacosis outbreaks in animal and bird parks in the whole country. For individual prevention of psittacosis, education of animal dealers and general pet owners should be encouraged. Up-to-date information should also be propagated to physicians and veterinarians for more understanding psittacosis including rapid diagnosis.
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