Chlamydia felis

Many metabolic processes and genes are highly conserved among Chlamydia.[6][2] Due to C. felis's, and Chlamydia in general, small genome, it is missing the genes for several essential enzymes for metabolic pathways, such as glycolysis and the citric acid cycle.[6] It cannot synthesize nucleotides, nor many cofactors or amino acids.[6] However, the bacteria's ability to synthesize and/or scavenge amino acids and nucleotides varies from species-to-species and from strain-to-strain, as shown by C. felis's ability to synthesize the tryptophan.[6][2] In order to survive, C. felis will take various metabolites, such as phosphorylated sugars, and other essential molecules from the host cell.[6] It is currently unknown exactly how the bacteria receive these molecules while residing in the inclusion.[6] It is thought that the bacteria receive host lipids by intercepting vesicles departing from the Golgi apparatus and by stealing lipid droplets and host lipid transfer proteins.[6] With the nutrients gathered from the host cell, the bacteria can perform glycolysis and the citric acid cycle.[6] The bacteria also have a fully functional electron transport chain (ETC), which includes a Na⁺ translocating NADH dehydrogenase, cytochrome bd oxidase, and a V-type ATPase.[6] C. felis uses oxygen as its terminal electron acceptor, in which the cytochrome bd oxidase is necessary.[6] The presence of a Na⁺ translocating NADH dehydrogenase suggests that instead of a proton-motive force, the bacteria uses a sodium-motive force for creating an electrochemical gradient across the plasma membrane.[6] C. felis has also been shown to have a complete pentose phosphate pathway (PPP) and gluconeogenesis pathway, as well as being capable of both creating and degrading glycogen.[6]

A bacterial culture was obtained by inoculating fertilized chicken eggs with C. felis.[2] After the strain had gone through several chicken egg passages, the strain went through four passages of McCoy cells before finally being used for genetic analysis.[2] The genome of C. felis was sequenced via whole genome shotgun.[2] Each gene was then annotated by programs BLASTP and FASTA.[2] Programs GenomeGambler, GeneHacker plus, and Glimmer 2.0 were used to predict protein-coding genes.[2] To search from transmembrane proteins, the program SOSUI was used, and tRNAscan-SE for tRNA genes.[2] C. felis has one circular chromosome that consists of around 1,100,00 base pairs.[2] Compared to non-pathogenic organisms, the size of the C. felis is relatively small.[6] The genes that C. felis does possess encode over 1,000 proteins.[2] Many of the genes are highly conserved within the Chlamydia genus.[2]

A specific plasmid is also highly conserved among Chlamydia.[2] The plasmid C. felis possess is called pCfe1 and is about 7,500 base pairs long.[2] A recent study has suggested that the plasmid is necessary for pathogenicity, though the exact mechanism is currently unknown.[8]

C. felis was originally discovered in the lungs of cats suffering from pneumonia.[4] C. felis used to be considered a strain of another member of its genus, C. psittaci until it was recognized as a separate species and reclassified as Chlamydophila felis.[2] Chlamydophila felis was then reclassified to Chlamydia felis due to dispute on the taxonomic usage of Chlamydophila, which is still disputed to this day.[3] C. felis is found worldwide.[9] It has been reported to infect humans as well, giving it zoonotic potential, though it is rare.[9] Humans that are infected can suffer from conjunctivitis and/or respiratory problems.[10] As typical of many members of its genus, C. felis is well adapted to live within its host and cannot survive for long outside of the host.[11] Thus, direct contact is necessary for the pathogen to spread and is why C. felis infection is more common in multi-cat environments.[11]

Infected cats typically contract conjunctivitis within a 2-5 day incubation period.[12] Clinical signs of infection are hyperaemia of the nictitating membrane (severity varies), blepharospasm, and discharge from the eye.[7][12][13] The infection is not deadly, but if left untreated may cause blindness and pain for the cat.[14] Infection is commonly spread among cats by ocular secretion.[7] C. felis infection is most common in multicat environments such as shelters, breeder catteries, and among stray cat communities.[7] Young cats, around the age of one year or under, are at the highest risk of infection.[7] Infection can be detected either by culturing a sample or by PCR.[7] Ocular samples are the most common, but samples can also be oropharyngeal, nasal, and/or oral.[7] The infection can be treated with antibiotics, typically with tetracyclines.[7] Vaccines for C. felis, both attenuated and inactivated, are available for cats.[7] For immunocompromised cats it is recommended that they only receive the inactivated vaccine, and only if necessary.[7]

C. felis typically has low zoonotic potential which is the likelihood that a pathogen can be spread from animal to human and still cause disease.[10] People who own or handle cats regularly are at a higher risk of contracting an infection from an afflicted cat.[10] The risk is even higher if the individual is immunocompromised or if there is poor hygiene.[10] In humans, C. felis could cause conjunctivitis, various respiratory problems, and other diseases.[10] Since most human cases are asymptomatic, it is possible that this zoonosis occurs more often than we know.[10]

C. felis is a common cause of conjunctivitis and upper respiratory problems in cats.[14] If left untreated, it leads to damage in the eyes followed by a loss of vision and, eventually, blindness.[14] While this is not fatal, it is still very uncomfortable for the cat.[14] Many countries do have a vaccine available.[10]

Up to 95% of cats with this infection come from shelters that have poor hygiene practices.[10] The presence of other animals, like in an animal shelter, increases prevalence.[10] This could have an impact on the adoption rates of animals in infected shelters.[15] People generally prefer cats that appear happy, healthy, and playful.[15] However, some cats are adopted out of pity.[15]

C. felis has been isolated from up to 30% of cats with conjunctivitis or upper respiratory tract disease.[16] Doxycyline is an antibiotic that is commonly used to treat these infections at a dosage of 10 mg/kg of body weight daily for four weeks.[13] One 100 mg capsule can cost anywhere from $0.61 to $13.26 USD.[17] This cost of treatment can be financially limiting considering that all cats within a facility, shelter, or home must be treated regardless of whether they are infected to ensure the disease is effectively eradicated.[13]