Chlamydial infection in animals

Chlamydophila pecorum

Clinical presentations

Encephalomyelitis

This disease is characterized by a systemic chlamydial infection, with several organs involved, most notably the nervous system. Recovery depends on the extent of central nervous system involvement (Perez-Martinez & Storz, 1985). Clinically, progressive weakness leads to paralysis, with death in 60% of affected animals 10-14 days after the onset of signs. The disease may remain enzootic, leading to outbreaks in newly introduced cattle (Harshfield, 1970). Schachter et al., 1975 showed by serotyping that a chlamydial strain associated with sporadic bovine encephalomyelitis(SBE) was distinct from strains associated with chlamydial abortion in cattle. C. pecorum strain ATCC VR-628, originally isolated from the brain of a calf with SBE ( McNutt & Waller, 1940), was proposed as the type strain for the species.

Pneumonia

Chlamydial-induced pneumonia in sheep was described as an interstitial bronchopneumonia , spreading from the bronchioles to the lung parenchyma (Dungworth & Cordy, 1962). White, 1965 was able to experimentally produce chlamydial pneumonia in young calves with a chlamydial isolate obtained from calves with pneumonia (Harbourne 1966). Calves with pneumonia have a serous, mucous or mucopurulent nasal discharge, are febrile and depressed, with a dry cough and dyspnoea. Usually the animals recover, but some remain chronically debilitated (Storz, 1971).

Polyarthritis

This disease has been described in sheep (Storz et al., 1963) and calves (Storz et al., 1966) in the USA.

In sheep, it presents as a seasonally influenced syndrome, characterised by fever, stiffness, lameness, anorexia and, frequently, conjunctivitis. Infection of the synovial tissues and associated inflammation of limb joints leads to stiffness and lameness, but joint enlargement is not usual except in long-term cases. Most lambs will overcome their stiffness with forced exercise.

In cattle, the disease is more serious and mortality is high. Infected calves are weak and stiff. Fever and diarrhoea may result. Joints, which may be grossly enlarged, are painful on palpation. Death may occur 2-10 days after the appearance of clinical signs (Storz et al., 1966).

Conjunctivitis

In sheep, chlamydial organisms have been recovered from cases of follicular conjunctivitis (Storz et al., 1967) and keratoconjunctivitis (Dickinson & Cooper, 1959). These conditions may occur in association with pneumonia or polyarthritis and may reflect localized or systemic infection. In lambs with conjunctivitis, 10-85% were found to have polyarthritis and, conversely, nearly all lambs with polyarthritis had conjunctivitis.

Early signs of chlamydial conjunctivitis in sheep included chemosis and dilation of conjunctival vessels. As the disease progresses, abundant seropurulent eye discharge is seen, sealing the eyelids in a crust. Severe inflammatory involvement is followed by neovascularisation of the cornea [new blood vessel formation], with both eyes equally affected in the majority of lambs (Stephenson et al., 1974). In uncomplicated cases, the disease is self-limiting, with full resolution of lesions.

Cattle affected by polyarthritis and pneumonia may also have conjunctivitis (Storz, 1971). Chlamydial isolates have been recovered from bovine keratoconjunctivitis cases (Dyml, 1965).

Enteritis

The intestinal tract may be the natural habitat for certain chlamydial [presumably C. pecorum] strains (Storz, 1971). However, intestinal infections may be overlooked as they are often asymptomatic, both in sheep (Wilson & Dungworth, 1963) and cattle (Wilson, 1962; Perez-Martinez & Storz, 1985). In lambs with intestinal infections, diffuse proliferation of intestinal lymphoid tissue and enlargement of the mesenteric lymph nodes were associated with a marked thickening of the terminal ileum (Piennar & Schutte, 1975).The shedding of infectious chlamydiae in faeces is likely to be an important means by which infections are spread in animals [see: C. pecorum: Epidemiology]. Stressing of carrier animals may precipitate chlamydial shedding and the onset of overt disease (Storz, 1971).

In cattle, intestinal infection with chlamydiae may result in diarrhoea in calves, in which the mucosa of the entire intestine may be congested and petechiated (Doughri et al., 1974). Chlamydiae have also been isolated from the faeces of clinically normal calves (Wilson, 1962; Wilson & Dungworth, 1965).

Metritis and infertility

In cattle, the ability of C. pecorum to cause endometritis has been demonstrated experimentally. Approximately 2-3 days after the inoculation of C. pecorum, the cows were depressed and anorexic, with a thick, yellowish vaginal discharge (Bowen et al., 1978; Wittenbrink et al., 1993). In some cases, a moderate, chronic endometritis developed. At necropsy, the uterus was filled with a purulent exudate. Cattle infected with C. pecorum had reduced fertility. In cattle experimentally infected with C. abortus strains, a sub-acute metritis developed which was less severe than that seen with C. pecorum. A serological survey of chlamydial antibody in cattle showed higher CFT titres in 2326 aborting cows compared to 1310 normally calving animals (Wilsmore & Dawson, 1986), [ PICK Comment: presumably mainly due to C. abortus].

NEXT: C. pecorum : Laboratory diagnosis.

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Topic revision: r2 - 2011-04-01 - MeWard
 
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