zoonoses and communicable diseases common to ... - PAHO/WHO

NECROBACILLOSIS 191Occurrence in Man: Advances in laboratory technology for the isolation ofanaerobes have led to greater recognition of their role in human pathology and, consequently,to an increase in the number of recorded cases in medical facilities.Occurrence in Animals: Some diseases, such as foot rot in sheep, occur frequentlyin all countries where sheep are raised. Others, such as calf diphtheria(necrobacillary stomatitis), are less common. Bovine hepatic necrobacillosis causesappreciable economic losses in many countries due to confiscation of animals inslaughterhouses; it is more frequent in areas where cattle are fed grain in feedlots(Timoney et al., 1988).The Disease in Man: F. necrophorum causes a wide variety of necrotic lesions,empyema, pulmonary abscesses, arthritis, and ovariosalpingitic sepsis. Bacteroidesfragilis and F. necrophorum are important agents of cerebral abscesses and, occasionally,of meningitis, almost always as a consequence of an otitis media (Islam andShneerson, 1980). The formerly high incidence of septicemia caused by F.necrophorum in children and adolescents who had suffered from tonsillitis(Lemierre’s syndrome) has now diminished notably and constitutes only 1% to 2%of all bacteremias caused by anaerobes. Patients with septicemia usually exhibitexudative pharyngitis or a peritonsillar abscess, but these symptoms may disappearby the time some patients obtain medical attention (Seidenfeld et al., 1982). In mosthuman clinical specimens, only the genera Bacteroides, Prevotella, Porphyromonas,and Fusobacterium should be considered among the anaerobic bacilli (Jousimies-Somer and Finegold, 1991). Infections in man come from the normal flora of adjacentcavities.The most effective antibiotics for treating infections caused by gram-negativeanaerobes are metronidazole, chloramphenicol, and imipenem (Jousimies-Somerand Finegold, 1991).The Disease in Animals: F. necrophorum is more important in animal than inhuman pathology and is the cause of several common diseases.SHEEP: Foot rot is the most common cause of lameness in sheep. The diseasebegins with interdigital dermatitis, progresses to the epidermal matrix of the hooves,and then causes destruction of the interdigital skin and detachment of the hoof.Environmental factors, such as wet soil and grass that soften the feet, are involvedin producing the disease, along with two bacterial agents, F. necrophorum andBacteroides nodosus. F. necrophorum establishes itself first and causes inflammationand destruction of the epidermis before penetrating to deeper layers. Hoofdegeneration is due to the proteolytic properties of B. nodosus. The disease mayappear in several forms: benign, usually caused by less virulent strains of B.nodosus; virulent, with deformation and detachment of the hoof; and chronic, whichmay last years, with or without producing lameness.Other hoof diseases affecting sheep are interdigital dermatitis and infectious bulbarnecrosis. The former, caused by F. necrophorum, is characterized by an edematousand erythematous inflammation of the interdigital skin, which may be coveredby a layer of moist, gray, necrotic material. Infectious bulbar necrosis is caused byF. necrophorum and Corynebacterium pyogenes and is characterized by abscessesand suppuration of the bulbar area of the hoof, particularly on the hind feet. The diseaseresults from the interaction of both bacteria. C. pyogenes produces a factor that