''Chlamydia psittaci'' is a lethal intracellular bacterial species that may cause

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

avian chlamydiosis,

epizootic In epizoology, an epizootic (or epizoötic, from Greek: ''epi-'' "upon" + ''zoon'' "animal") is a disease event in a nonhuman animal population analogous to an epidemic in humans. An epizootic disease (or ) may occur in a specific locale (an ...

outbreak In epidemiology, an outbreak is a sudden increase in occurrences of a disease when cases are in excess of normal expectancy for the location or season. It may affect a small and localized group or impact upon thousands of people across an entire ...

s in other

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s, and respiratory psittacosis in

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s. Potential hosts include feral birds and domesticated poultry, as well as

cattle Cattle (''Bos taurus'') are large, domesticated, bovid ungulates widely kept as livestock. They are prominent modern members of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Mature female cattle are calle ...

pig The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...

sheep Sheep (: sheep) or domestic sheep (''Ovis aries'') are a domesticated, ruminant mammal typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to d ...

, and

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...

s. ''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 Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...

. 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 w ...

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

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

of infected animals of all sorts. ''Chlamydia psittaci'' in birds is often systemic, 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 a thin, continuous, protective layer of Cell (biology), cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial (Mesothelium, mesothelial) tissues line ...

s and

macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

s of the

respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respirato ...

Septicaemia Sepsis is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage of sepsis is followed by suppression of the immune system. Common signs and s ...

eventually develops and the bacteria become localized in

epithelial cells Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

and macrophages of most

organ Organ and organs may refer to: Biology * Organ (biology), a group of tissues organized to serve a common function * Organ system, a collection of organs that function together to carry out specific functions within the body. Musical instruments ...

conjunctiva In the anatomy of the eye, the conjunctiva (: conjunctivae) is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with gobl ...

, and

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

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 ...

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 cell (biology), cells are grown under controlled conditions, generally outside of their natural environment. After cells of interest have been Cell isolation, isolated from living tissue, ...

, have

16S rRNA 16S ribosomal RNA (or 16Svedberg, 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 genes coding for it are referred to as ...

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

s 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 Cell (biology), cells are classified together based on their shared reactivity ...

s. All should be considered to be readily transmissible to humans. ''Chlamydia psittaci'' serovar A is endemic among psittacine birds and has caused sporadic

zoonotic A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a virus, bacterium, parasite, fungi, or prion) that can jump from a non-human vertebrate to a human. When h ...

disease in humans, other mammals, and

tortoise Tortoises ( ) are reptiles of the family Testudinidae of the order Testudines (Latin for "tortoise"). Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like o ...

s. 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 Dairy cattle (also called dairy cows) are cattle bred with the ability to produce large quantities of milk, from which dairy products are made. Dairy cattle generally are of the species '' Bos taurus''. Historically, little distinction was ...

. Serovars C and D are occupational hazards for

slaughterhouse In livestock agriculture and the meat industry, a slaughterhouse, also called an abattoir (), is a facility where livestock animals are slaughtered to provide food. Slaughterhouses supply meat, which then becomes the responsibility of a mea ...

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 A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

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 virus that infects and replicates within bacteria. The term is derived . Bacteriophages are composed of proteins that Capsid, encapsulate a DNA or RNA genome, and may have structu ...

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

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

s. 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 Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

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 Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of the endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membra ...

phagocytosis Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...

. However, the EB is not destroyed by fusion with

lysosome A lysosome () is a membrane-bound organelle that is found in all mammalian cells, with the exception of red blood cells (erythrocytes). There are normally hundreds of lysosomes in the cytosol, where they function as the cell’s degradation cent ...

s, 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'', 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 ''C. psittaci'' abortion, ''C. psittaci'' feline, and ''C. psittaci''

guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy ( ), is a species of rodent belonging to the genus ''Cavia'', family Caviidae. Animal fancy, Breeders tend to use the name "cavy" for the ani ...

are since 1999 three separate species, '' C. abortus'', '' C. felis'', and '' C. caviae''. New species continue to be described from inside of what was thought to be ''C. psittaci''. Being a pathogen with a very broad host range, ''C. psittaci'' has a lot of opportunities to recombine with other ''Chlamydia''. Genotypes of ''C. psittaci'' are defined by the partial ompA sequence, which is immunologically relevant and can be amplified by PCR. The main types are A-F, E/B, with G, G1, G2, 1V, 6N, Mat116, R54, YP84, CPX0308, I, and J considered provisional. This has since been expanded into a seven-partial-gene MLST scheme. The MLST scheme technically yields "sequence types" distinct from genotype assignment, but it usually recovers the genotype grouping anyways.

Psittaci-abortus intermediate

Phylogenetic trees show a relatively recent branch between ''C. psittaci'' and ''C. abortus''. There are also many strains intermediate in position between strains clearly defined as belonging in either species, such as 84/2334 isolated from a parrot. Vafin et al. (2007) believe that this intermediate position should be its own species "''C. parapsittaci''", which includes the genotypes C (strains GD, CT1, Par1), D (NJ1, 92-1293, TT3, 7344/2), G (strains Rostinovo-70, 250, PP-87, KC-93), F (strains VS225, 7778B15), and non-grouped strains WC, 84/2334, and R54. Genotypes C, D, and F are isolated from avians; G is isolated from livestock abortions in the former Soviet Union; and WC was isolated from a mammal. For the Rostinovo-70 strain, ''omp1'', ''omp2'', 16S, 23S, plasmid (all partial) sequences are available. All G genotype strains have the exact same plasmid sequence as the one in 84/2334, and the exact same 23S sequence as the three strains from genotype C. Two provisional genotypes were defined in 2017: G1, G2. These too reflect an intermediate position, though because the author was unaware of Vafin's results, there was no comparison with Vafin's ompA sequences. A new species was effectively published in 2019, ''C. buteonis'', which consisted of one type strain RSHA from a red-shouldered hawk. This species occupies an intermediate position. Longbottom et al. (2021) sequenced the whole genome of 84/2334. They find its entire genome, alongside that of genotypes G1 and G2, to be closer to ''C. abortus'' than to ''C. psittaci'', despite the fact that it has a plasmid (typical ''C. abortus'' does not carry one). Analyses of seven MLST housekeeping gene fragments also find the same for genotype 1V, leading to the suggestion to transfer these three genotypes plus 84/2334 to ''C. abortus''. On the other hand, ''C. buteonis'' was shown to be closer to ''C. psittaci'' than to ''C. abortus'' on MSLT, and intermediate with a long branch of its own on whole-genome NeighborNet. Vafin's four strains were not analyzed. WC and genotypes C, D, F were solidly placed in ''C. psittaci''.

Diseases

''Chlamydia 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 A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

reduction. Most ''C. psittaci'' genomes encode between 1,000 and 1,400

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s. 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, microimmunofluorescence, and

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...

tests can be used to confirm the diagnosis.

Treatment

Tetracycline Tetracycline, sold under various brand names, is an antibiotic in the tetracyclines family of medications, used to treat a number of infections, including acne, cholera, brucellosis, plague, malaria, and syphilis. It is available in oral an ...

macrolide Macrolides are a class of mostly natural products with a large macrocyclic lactone ring to which one or more deoxy sugars, usually cladinose and desosamine, may be attached. Macrolides belong to the polyketide class of natural products. ...

s 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. Cannabis or tobacco smoke should be avoided. While taking tetracycline, dairy products should be avoided.