Introduction.pdf

Introduction caviae and Chlamydophila felis, which generally infect Chlamydophila felis (previously feline Chlamydia birds, sheep, guinea-pigs and cats, respectively. psittaci) was first isolated in hens’ eggs in the USA Chlamydia trach...

Introduction caviae and Chlamydophila felis, which generally infect Chlamydophila felis (previously feline Chlamydia birds, sheep, guinea-pigs and cats, respectively. psittaci) was first isolated in hens’ eggs in the USA Chlamydia trachomatis is a well-characterised from cats with respiratory disease in 1942 (Baker, species. In humans, certain serovars of C. trachomatis 1942). Because C. felis was the first feline respiratory are responsible for a chronic keratoconjunctivitis pathogen to be identified, it was initially believed that known as trachoma, a major public health problem in most cases of feline upper respiratory tract disease developing regions such as North Africa and southeast (URTD) were the result of chlamydial infection.With Asia (Stamm, 1998). Other serovars cause mainly the isolation of feline calicivirus (FCV) and feline ocular, genital, or both ocular and genital infections herpesvirus-1 (FHV-1) in the late 1950s, the importance in humans, which are spread mainly by sexual of C. felis was questioned. In the late 1970s, however, transmission a number of studies re-emphasised its importance with occasional ocular transfer. Chlamydia as a conjunctival pathogen of cats. There is some pneumoniae is a major cause of pneumonia in evidence humans, and has also been associated with acute to that C. felis may occasionally be associated with chronic bronchitis, sinusitis, pharyngitis, coronary other clinical signs, such as vaginal discharge, although artery disease, asthma, cerebrovascular disease, much remains to be learned about the importance of sarcoidosis and reactive arthritis. Chlamydophilia these conditions. psittaci and C. abortus are zoonoses, causing Aetiology respiratory Chlamydiae are obligately intracellular Gram-negative and reproductive disease, respectively. bacteria. Unlike viruses, they possess both DNA and Serological studies suggest that multiple strains of RNA, their replication cycle involves binary fission C. felis exist, which may differ in virulence (Yerasimides, and they are susceptible to certain antimicrobial 1960; Kuroda-Kitogawa et al., 1993). drugs. Unlike Rickettsiae, they lack a cytochrome Randomamplification of polymorphic DNA system for electron transport and cannot synthesise fingerprinting adenosine triphosphate (ATP) and guanosine has demonstrated the existence of at least two feline triphosphate strains (Pudjiatmoko et al., 1997). Although the (GTP). Their cell walls show similarity to those major site of antigenic variation in C. trachomatis is of Gram-negative bacteria, and their DNA is also in the major outer membrane protein gene (ompA), contained within nucleoids that are not separated DNA analysis has shown that ompA is highly conserved from the cytoplasm by a membrane. The genome between different C. felis isolates (Sayada et al., sizes of Chlamydia psittaci and Chlamydia trachomatis 1994;May et al., 1996; Sykes, 1997). have been estimated to be around 1450 kb (Frutos The chlamydial developmental cycle involves an et al., 1989). alternation between the predominantly extracellular, Chlamydiae are placed within the order Chlamydiales infectious elementary body (EB), measuring 0.3_m and family Chlamydiaceae. Until recently, in diameter, and the intracellular, metabolically active a single genus, Chlamydia, was recognised, containing reticulate body (RB), measuring 0.5–1.5_m in diameter. the four species C. trachomatis, C. psittaci, C. Only the RB can divide, which occurs in an intracellular pneumoniae vacuole called an inclusion. The length of the and C. pecorum. However, results of 23S cycle in cell culture varies from 48 to 72 h. The RBs rRNA gene analysis have shown that chlamydiae can then reorganise into EBs, which are subsequently be divided into nine groups, which correlate with the released from the host cell and may enter a new, host species infected. Therefore, Chlamydiae have uninfected now been reclassified into nine species belonging to host cell, where they reorganise into RBs. two genera, Chlamydia and Chlamydophila (Everett Chlamydial EBs survive for only a few days at room et al., 1999). The genus Chlamydia includes Chlamydia temperature. Survival for up to 1 month at 4°C may trachomatis, infecting humans, Chlamydia muridarum, be possible (Baker, 1942). They are inactivated by infecting rodents, and Chlamydia suis, infecting lipid solvents and detergents, but are somewhat swine. Chlamydophila comprises Chlamydophila resistant to acids and alkalis. pecorum (previously Chlamydia pecorum), which Pathogenesis infects cattle and sheep, Chlamydophila pneumoniae Much remains unknown regarding the pathogenesis (previously Chlamydia pneumoniae), as well as four of chlamydial infections in cats. The organism new appears to have a predilection for the conjunctival species derived from Chlamydia psittaci: Chlamydophila epithelial cell. Natural transmission of C. felis, as for psittaci, Chlamydophila abortus, Chlamydophila the other respiratory pathogens, presumably occurs by close contact with other infected cats and their FCV infection had additional signs, such as oral aerosols, and via fomites. Mutual grooming and ulceration, selfgrooming in addition to conjunctivitis. Dual infection are probably important means of natural with FCV appears to be more common than with inoculation. It is unclear whether natural transmission FHV-1, although this may relate to the ease of by the venereal route occurs in cats. The incubation detection period in experimentally infected cats is of FCV compared with FHV-1.Coinfections with approximately 3–5 days. feline immunodeficiency virus (FIV) prolong the Infections caused by chlamydiae tend to follow a duration of conjunctivitis and chlamydial shedding chronic, insidious course, often progressing through and, in cats with existing FIV infection, superinfection asymptomatic stages. chlamydiae may be capable of with C. felis may accelerate the clinical progression of passing through periods of delayed development FIV infection (O’Dair et al., 1994). Both Mycoplasma interspersed species and Bordetella bronchiseptica can complicate with production of new crops of infectious EBs. C. felis infections (Shewen et al., 1980; Sykes, 1997). Human chlamydial infections of up to 20 years’ Other bacteria, including those that normally colonise duration the healthy conjunctival sac, can also act as secondary have been reported in the literature. It is unclear invaders and worsen disease. whether chronic disease is the result of repeated Clinical signs reinfection Respiratory and ocular disease or the presence of persistent chlamydiae. Since the discovery of C. felis, there has been much Persistent chlamydiae in the form of atypical RBs controversy regarding the extent of disease attributable have been identified in the joints of humans with to the organism. Chlamydophilia felis is primarily a reactive arthritis. Localisation of persistent Chlamydiae conjunctival pathogen, capable of causing acute to to deeper tissues, such as the subsynovial layer in chronic conjunctivitis, with blepharospasm, chemosis patients with arthritis (Beutler et al., 1995),may afford and congestion and a serous to mucopurulent ocular protection from the continual rapid cell turnover discharge, but no dyspnoea or coughing (Plates 27.1 characteristic of epithelial tissues. and 27.2). Mild pulmonary lesions may result from Chlamydophilia felis may also be capable of entering aerosol exposure (Hoover et al., 1978), but as these are a persistent state within tissues. Conjunctivitis clinically insignificant, C. felis is no longer known as the associated with C. felis may persist for several months. ‘feline pneumonitis agent’. Transient pyrexia, reduced Organisms have been isolated from the conjunctiva appetite and weight loss may occur shortly after for up to 215 days after experimental infection, infection, although most cats cease conjunctival shedding at although many cats remain well and continue to around 60 days after infection (Wills, 1986; O’Dair eat. An acute-phase reactant response was shown to et al., 1994). Persistent elevations in serum titres to C. accompany pyrexia in experimentally infected cats felis, despite apparent cessation of shedding, also (TerWee et al., 1998). Clinical signs improve after a few suggest weeks, but mild conjunctivitis frequently persists for that some cats may be capable of harbouring several months. Nasal discharge and sneezing may persistent chlamydiae. The intestinal tract may be occur in some cats. The strain and/or the route of a site of persistent infection in cats, as has been infection shown in birds and ruminants. Prolonged rectal and may influence the extent of respiratory tract vaginal excretion by cats with experimentally induced involvement. Sneezing and nasal discharge without chlamydial conjunctivitis has been documented concurrent ocular involvement is highly unlikely to be (Wills, 1986). The occasional finding of C. felis in the associated with C. felis infection (Sykes et al., 1999b). spleen, liver and peritoneum of cats has not been In contrast to ocular chlamydial infections of other consistent, host species, C. felis infection is rarely associated with and the significance of the presence of organisms corneal damage. Reported cases of corneal in these locations remains unclear (Baker, 1944; involvement, Dickie & Sniff, 1980; Hoover, 1980). including punctate keratitis and scarring, did Chlamydial disease may be exacerbated by not exclude the possibility that corneal disease was superinfection attributable to dual infection with other pathogens, with other microorganisms. In one study, 8% such as FHV-1 (El-Sheikh, 1978; Tabatabayi & Rad, of cats had both chlamydial and either FCV or FHV-1 1981). One study showed that simultaneous inoculation infection (Wills et al., 1988a). Cats with concurrent of a Streptococcus species isolate with C. felis was more likely to be associated with keratoconjunctivitis. Corneal ulceration occurred in half of the cats infected (Darougar et al., 1977). The ability of the organism to cause corneal disease may also be dependent on strain and/or host factors. Chlamydophilia felis has occasionally been isolated from cases of neonatal conjunctivitis in kittens (Sykes, 1997; Wills & Gaskell, 1994), although most kittens appear to be protected by maternally derived antibody (MDA; see below) (Plate 27.3).Whether or not such cases are associated with genital infection in the queen, as occurs in humans infected with C. trachomatis, is unclear.