''Chlamydia psittaci'' is a lethal intracellular bacterial species that may cause endemic avian chlamydiosis, epizootic outbreaks in

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s, and respiratory

psittacosis Psittacosis—also known as parrot fever, and ornithosis—is a zoonotic infectious disease in humans caused by a bacterium called ''Chlamydia psittaci'' and contracted from infected parrots, such as macaws, cockatiels, and budgerigars, and from ...

in humans. Potential hosts include feral birds and domesticated poultry, as well as cattle, pigs, sheep, and horses. ''C. psittaci'' is transmitted by inhalation, contact, or ingestion among birds and to mammals. Psittacosis in birds and in humans often starts with flu-like symptoms and becomes a life-threatening pneumonia. Many strains remain quiescent in birds until activated by stress. Birds are excellent, highly mobile vectors for the distribution of

chlamydia infection Chlamydia, or more specifically a chlamydia infection, is a sexually transmitted infection caused by the bacterium ''Chlamydia trachomatis''. Most people who are infected have no symptoms. When symptoms do appear they may occur only several we ...

, because they feed on, and have access to, the

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

of infected animals of all sorts. ''C. psittaci'' in birds is often

systemic Systemic fundamental to a predominant social, economic, or political practice. This refers to: In medicine In medicine, ''systemic'' means affecting the whole body, or at least multiple organ systems. It is in contrast with ''topical'' or ''loc ...

, and infections can be inapparent, severe, acute, or chronic with intermittent shedding. ''C. psittaci'' strains in birds infect mucosal

epithelial cell Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

s and

macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer cel ...

s of the

respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to th ...

. Septicaemia eventually develops and the bacteria become localized in epithelial cells and macrophages of most

organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard instrument ** Hammond ...

s, conjunctiva, and

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syste ...

s. It can also be passed in the

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

s. Stress will commonly trigger onset of severe symptoms, resulting in rapid deterioration and death. ''C. psittaci'' strains are similar in virulence, grow readily in

cell culture Cell culture or tissue culture is the process by which cells are grown under controlled conditions, generally outside of their natural environment. The term "tissue culture" was coined by American pathologist Montrose Thomas Burrows. This te ...

, have

16S rRNA 16S rRNA may refer to: * 16S ribosomal RNA 16 S ribosomal RNA (or 16 S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome ( SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The g ...

genes that differ by <0.8%, and belong to eight known

serotype A serotype or serovar is a distinct variation within a species of bacteria or virus or among immune cells of different individuals. These microorganisms, viruses, or cells are classified together based on their surface antigens, allowing the epi ...

s. All should be considered to be readily transmissible to humans. ''C. psittaci'' serovar A is endemic among

psittacine Psittacinae is a subfamily of Afrotropical or Old World parrots, native to sub-Saharan Africa, which include twelve species and two extant genera. Among the species is the iconic grey parrot. The ''Poicephalus'' are usually green birds with dif ...

birds and has caused sporadic zoonotic disease in humans, other mammals, and tortoises. Serovar B is endemic among pigeons, has been isolated from turkeys, and has also been identified as the cause of abortion in herds of dairy cattle. Serovars C and D are

occupational hazards Employment is a relationship between two party (law), parties Regulation, regulating the provision of paid Labour (human activity), labour services. Usually based on a employment contract, contract, one party, the employer, which might be a co ...

for

slaughterhouse A slaughterhouse, also called abattoir (), is a facility where animals are slaughtered to provide food. Slaughterhouses supply meat, which then becomes the responsibility of a packaging facility. Slaughterhouses that produce meat that is no ...

workers and for people in contact with birds. Serovar E isolates (known as Cal-10, MP or MN) have been obtained from a variety of avian hosts worldwide and, although they were associated with the 1920s–1930s outbreak in humans, a specific reservoir for serovar E has not been identified. The M56 and WC serovars were isolated during outbreaks in mammals. Many ''C. psittaci'' strains are susceptible to

bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...

Life cycle and method of infection

''Chlamydia psittaci'' is a small bacterium (0.5μm) that undergoes several transformations during its lifecycle. It exists as an elementary body (EB) between hosts. The EB is not biologically active, but is resistant to environmental stresses and can survive outside a host. The EB travels from an infected bird to the

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

s of an uninfected bird or person in small droplets, and is responsible for infection. Once in the lungs, the EB is taken up by cells in a pouch called an endosome by phagocytosis. However, the EB is not destroyed by fusion with lysosomes, as is typical for phagocytosed material. Instead, it transforms into a reticulate body and begins to replicate within the endosome. The reticulate bodies must use some of the host's cellular machinery to complete their replication. The reticulate bodies then convert back to elementary bodies, and are released back into the lung, often after causing the death of the host cell. The EBs are thereafter able to infect new cells, either in the same organism or in a new host. Thus, the lifecycle of ''C. psittaci'' is divided between the elementary body which is able to infect new hosts, but can not replicate, and the reticulate body, which replicates, but is not able to cause new infection.

History

The disease caused by ''C. psittaci'', psittacosis, was first characterized in 1879 when seven individuals in Switzerland were found to experience pneumonia after exposure to tropical pet birds. The causative pathogen was not known. The related bacterial species ''Chlamydia trachomatis'' was described in 1907, but was assumed to be a virus, as it could not be grown on artificial media. In the winter of 1929–1930, a psittacosis pandemic spread across the United States and Europe. Its mortality rate was 20% and as high as 80% for pregnant women. The disease's spread was eventually attributed to exposure to Amazon parrots imported from Argentina. Though ''C. psittaci'' was identified in 1930 as the agent responsible for psittacosis, it was not found to be a bacterium until examination by electron microscopy in the 1960s.

Taxonomy

For several decades, the family Chlamydiaceae contained a sole genus, ''Chlamydia''. ''C. psittaci'' was originally classified from the 1960s to 1999 as a species of this sole genus. In 1999, the order Chlamydiales was assigned two new families (Parachlamydiaceae and Simkaniaceae), and within the family Chlamydiaceae, the genus ''Chlamydia'' was divided into two genera, ''Chlamydia'' and the newly designated genus ''

Chlamydophila ''Chlamydophila'' is a controversial bacterial genus belonging to the family Chlamydiaceae. Taxonomy All Chlamydiota are anaerobic bacteria with a biphasic developmental lifecycle that depends on obligately intracellular growth in eukaryotic h ...

'', with ''C. psittaci'' becoming ''Chlamydophila psittaci''. However, this reclassification "was not wholly accepted or adopted" among microbiologists, which "resulted in a reversion to the single, original genus ''Chlamydia'', which now encompasses all 9 species including ''C. psittaci''." A new species was added to the reunited genus ''Chlamydia'' in 2013, two more were added in 2014. What were once classified as the mammal-endemic strains ''C. psittaci'' abortion, C. psittaci''

feline Feline may refer to: Zoology * Loosely, Felidae, a member of the cat family, which includes the subfamilies Pantherinae and Felinae (conventionally designated a felid) ** Following the taxonomic convention, Felinae, the subfamily of Felidae that ...

, and ''C. psittaci'' guinea pig are today three separate species, '' C. abortus'', '' C. felis'', and '' C. caviae''.

Diseases

''C. psittaci'' infection is also associated with schizophrenia. Many other kinds of infections have been associated with schizophrenia.

Genomics

Like other Chlamydia, ''C. psittaci'' is an intracellular pathogen and has thus undergone significant genome reduction. Most ''C. psittaci'' genomes encode between 1,000 and 1,400 proteins. A total of 911 core genes were found to be present in all 20 strains sequenced by Read et al., corresponding to 90% of the genes present in each genome.

Confirmation of diagnosis

In addition to symptoms and CHX,

complement fixation The complement fixation test is an immunological medical test that can be used to detect the presence of either specific antibody or specific antigen in a patient's serum, based on whether complement fixation occurs. It was widely used to diagnos ...

microimmunofluorescence Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on microbiological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to sp ...

, and polymerase chain reaction tests can be used to confirm the diagnosis.

Treatment

Tetracycline or macrolides can be used to treat this condition. The drugs are given intravenously or orally, depending on drug choice. Treatment should continue for 10–14 days after the fever subsides. In children or pregnant women, though, tetracycline should not be used. Ibuprofen or acetominophen, and fluids are also administered. Cigarette or tobacco smoke should be avoided. While taking tetracycline, dairy products should be avoided.