The role of first line of defence mechanisms in the pathogenesis of cellulitis in broiler chickens: skin structural, physiological and cellular response factors.

The present study examined several basic attributes of first-line defence mechanisms in the skin as potential factors that may explain the susceptibility of broiler chickens to cellulitis. The variables including structural characteristics of the skin, physicochemical properties and cellular responses to the challenge with pathogens were compared between two categories of chickens, a strain of fast-growing commercial broiler chickens (susceptible to cellulitis) and leghorn chickens (resistant to cellulitis). There were substantial differences between leghorns and broilers with regard to physiological characteristics of the skin. Broiler skin was more amenable to injury and the wound-healing process was slow. Compared with leghorns, the lesions resulting from sub-dermal challenge in broilers were more severe and disseminated over a larger area. Mobilization of phagocytic cells (heterophils and macrophages) in leghorns was brisk even in the areas distant from the site of infection, whereas only few heterophils were recruited in the skin of broilers. The functional competence of heterophils in broilers was inferior when compared with leghorns. Based on the present finding, the predisposition of broilers to cellulitis appears to be primarily associated with the inferior first line of defence of their skin. Broilers in commercial situations may be at higher risk to succumb to even minor infection and eventually develop cellulitis because: (1) structural weaknesses of the skin may predispose broilers to skin injury and thus the risk of skin infection by pathogens is increased; (2) broiler skin surface is more likely to provide a conducive environment for colonization of Escherichia coli; (3) in the event of infection, poor recruitment of phagocytic cells to the site of infection may readily lead to widespread colonization of the tissue by pathogens causing cellulitis and (4) poor functional quality of the phagocytic cells that are mobilized compromise the ability of the host to contain the spread of infection.

Histopathologic and bacteriologic evaluations of cellulitis detected in legs and caudal abdominal regions of turkeys.

The objective of this study was to identify the causative agent of cellulitis in turkeys. Eighteen flocks from nine producers were sampled at the local processing plant, and 37 birds with cellulitis on legs or caudal thoracic area were obtained. None of the 37 birds with cellulitis had lesions in other organs. On gross examination, lesions were categorized into two groups: cellulitis with unopened skin lesions (type a) and cellulitis with opened skin lesions (type b). Histopathologically, cellulitis with unopened skin lesions had dermal necrosis with underlying fibrin and inflammatory exudate but cellulitis with open skin lesions had chronic granulomatous/granulation tissue-type reaction associated with foreign material. A complete bacteriologic study was conducted on 25 of 37 birds. Bacteria were isolated from 12 of the 25 birds with cellulitis lesions. No aerobic, microaerophilic, or anaerobic bacteria were isolated from the remaining 13 birds with cellulitis lesions. Escherichia coli was isolated in low numbers in mixed cultures with Proteus mirabilis, Lactobacillus spp., Klebsiella spp., and Staphylococcus spp. in 9 of 12 lesions. The remaining few cases yielded P. mirabilis in pure culture or in mixed culture with Pseudomonas aeruginosa. Types a and b cellulitis lesions in turkeys could be associated with primary contact dermatitis and skin abrasions, respectively. Their occurrence is likely associated with different management practices.

Cellulitis in broiler chickens: epidemiological trends, meat hygiene, and possible human health implications.

The present work evaluates trends in the incidence of cellulitis during the last decade using Canadian National Poultry Condemnation Records. In 1986, only 0.048% of the total slaughter broilers were condemned as a result of cellulitis lesions. Over the next 10 yr, steady increments in cellulitis condemnations were observed, and between 1986 and 1996, the percentage of cellulitis condemnation increased 11.8-fold. In 1996, more than 2.6 million broilers (0.568% of total slaughter) were condemned due to cellulitis; this constituted 30.1% of total condemnations, making it the number one condemnation category in 1996. In the context of dynamic increase in cellulitis, the problems concerning meat hygiene and possible health risk to the consumer are deliberated.

Left atrio-ventricular valve degeneration, left ventricular dilation and right ventricular failure: A possible association with pulmonary hypertension and aetiology of ascites in broiler chickens.

The results presented here are based on a collection of heart necropsy data obtained from a large population of ascitic and normal broiler chickens raised at low altitude. The hearts were subjected to gross postmortem evaluation. Generally, gross changes in the cardiac muscle predominantly consisted of various degrees of right and left ventricular enlargement and atrial enlargement, and were observed in all hearts from birds that developed ascites and in some apparently normal chickens. These hearts appeared flaccid, had a thin ventricular muscle wall, and lacked the normal tone of healthy heart muscle. Ventricular enlargement (mostly dilation) and AV valve degeneration (endocardiosis) were observed as early as 7 to 10 days of age and throughout the remaining growth period in broilers with or without ascites. The hearts from 264 ascitic and 255 apparently normal commercial broilers were used for quantitative analysis, with emphasis on dilatory changes of the ventriculi and detailed evaluation of the atrio-ventricular (AV) valves. The lesions of the AV apparatus and the degree of dilation of the ventriculi were graded according to a priori established standards, and categorized as mild, moderate or severe. Severe or moderate dilation of both the right and left ventricle were observed more frequently (P < 0.001) in ascitic birds than in normal birds. Of hearts from apparently normal birds, 34 and 61% had grossly normal right and left ventricle, respectively. Overall, 30% of ascitic birds had a grossly normal left ventricle, but some degree of right ventricular dilation was found in all ascitic birds. Prominent endocardiosis was a common feature in a majority of hearts from ascitic birds and in some apparently normal birds. Endocardiosis of the left AV valves was observed considerably more frequently (P < 0.001) than of right AV valves. Most severe lesions were found on left AV valves, and consisted of nodules or coalescing formations associated with annulus, valve cusps, chordae tendineae, and sometimes spread to the mural endocardium in the vicinity of the valve apparatus. Frequently the cusps appeared thickened and rigid, and had rolled edges. Chordae tendineae were frequently thickened, and sometimes ruptured. These severe left AV valve lesions were found most frequently (P < 0.001) in the hearts from ascitic birds (52%) in comparison to apparently normal birds (18%). The right AV valve lesions were mainly in the form of small nodules found around the orifice, and less frequently seen on the muscular leaflets of the right valve. Only in a few instances the nodules were larger, ranging from 1 to 3 mm in diameter. The severity of gross lesions on the left AV valve were indicative of stenosis and/or insufficiency of the valve apparatus. A hypothesis that left atrio-ventricular valve degeneration and left ventricular dilation should be considered as a possible aetiologic association with pulmonary hypertension, right ventricular failure, and ascites in broiler chickens is presented and discussed.

Isolation of Escherichia coli from cellulitis and other lesions of the same bird in broilers at slaughter.

Cellulitis results in substantial losses to the broiler industry due to condemnations at slaughter. This study was conducted to clarify the association between Escherichia coli isolated from cellulitis and other lesions caused by E. coli in individual birds. Fourteen flocks were sampled and 118 birds with cellulitis were examined. Escherichia coli was isolated from all but 2 of the cellulitis lesions, and serogroups O78, O1, and O2 predominated. Thirty-six birds had at least 1 other lesion in addition to the cellulitis lesion. Isolation of E. coli from cellulitis and other lesions occurred in 7 of the 14 flocks. Escherichia coli of the same serogroup were isolated from cellulitis and other lesions in some birds, suggesting that a single E. coli may sometimes be responsible for both types of lesions.