Update on the diagnosis and management of Macrorhabdus ornithogaster (formerly megabacteria) in avian patients

Macrorhabdus ornithogaster, a yeast found only at the junction between the ventriculus and proventriculus, can infect a wide range of birds. Infection is often subclinical but can also result in gastrointestinal signs. Direct observation of the organism in the feces is a specific but somewhat insensitive means of diagnosis. At least three antifungal drugs are reported to be effective for treatment but resistance to one or more of these drugs may occur.

Disseminated Aspergillus flavus infection in broiler breeder pullets

Increased morbidity and mortality occurred in a 5-wk-old broiler breeder replacement pullet flock. The affected broiler pullet flock was housed on the first floor of a two-story confinement building. Mortality increased to 0.1%/day compared to the flock on the second floor, which had mortality levels of less than 0.01%/day. Clinical signs in the affected chickens included inactivity, decreased response to stimuli, and anorexia. No respiratory or neurologic signs were observed. On necropsy, affected pullets were dehydrated and emaciated and had disseminated variably sized single or multiple heterophilic granulomas that contained intralesional septate and branching fungal hyphae. Lesions were extensive around the base of the heart in the thoracic inlet and in the kidneys. Other affected organs included eyelid, muscle, proventriculus, ventriculus, intestine, liver, spleen, lung, and heart. Aspergillus flavus was cultured from the visceral granulomas. The source of flock exposure to the organism was not determined.

Viral and bacterial agents associated with experimental transmission of infectious proventriculitis of broiler chickens

Proventriculitis of broilers can be reproduced by oral inoculation of day-old chicks with a proventricular homogenate from affected 3-wk-old broilers. The objective of the following studies was to isolate from this homogenate viral and bacterial isolates that could produce proventriculitis. A monoclonal antibody to infectious bursal disease virus (IBDV) was used to precipitate virus from the homogenate. A primary chicken digestive tract cell culture system was also used to isolate virus from a 0.2-microm filtrate of the homogenate, and a bacterium was also isolated from the homogenate. In trial 1, day-old birds were orally inoculated with either proventriculus homogenate or monoclonal antibody immunoprecipitated IBDV (MAB-IBDV). At 4, 7, 14, and 21 days postinfection (PI), 12 birds from each treatment group were subjected to necropsy. In trial 2, day-old birds were orally inoculated with either infectious proventriculus homogenate, suspect virus isolated in cell culture and propagated in embryo livers and spleens, or a bacterial isolate. Twelve birds from each treatment were subjected to necropsy at days 7, 14, 21, and 28 PI. In trial 3, treatments were maintained in negative pressure isolation chambers, and an additional treatment included virus plus bacterial isolate. Twenty-four birds from each treatment were subjected to necropsy at day 21 PI. In trial 1, infectious homogenate decreased body weight and relative gizzard weights at 4, 7, 14, and 21 days PI. Proventriculus relative weight was increased at days 7, 14, and 21 PI, and proventriculus lesion scores were increased at days 14 and 21 PI. Bursa/spleen weight ratios were decreased at day 14, and feed conversion was increased at days 4 and 21. The MAB-IBDV treatment decreased proventriculus and gizzard relative weights at day 4 PI, increased proventriculus lesion scores and bursa/spleen weight ratios at day 14, and decreased heterophil/lymphocyte ratios at day 21. In trial 2, all infected birds had significantly higher mean relative proventriculus weights at 21 days PI and had higher 4-wk mean proventriculus scores as compared with both control groups. In trial 3, birds treated with homogenate and birds treated with both suspect virus and the bacterial isolate had significantly higher proventriculus lesion scores; higher relative weights of proventriculus, gizzard, liver, and heart; lower body weights; and lower relative bursa weights compared with the saline control group. These studies suggest that infectious proventriculitis has a complex etiology involving both viral and bacterial infection.

[Megabacteria-associated proventriculitis in poultry in the state of Brandenburg, Germany]

During the second half of the year 2000, we have diagnosed a megabacterial-associated proventriculitis in 13 laying hens and 4 cocks from 14 different flocks and one turkey. All birds were submitted for necropsy because of progressive runting, increased mortality and poor laying performance in the herds. Routine diagnostic workup included necropsy, histology, bacteriology, parasitology and virology. At necropsy, the proventricular of the birds were enlarged. The walls were thickened and the mucosa covered with cloudy, grey-white mucus. Petechial haemorrhages and ulcerations predominantly at the proventricular-ventricular junction and sloughing of the necrotic koilin layer of the ventriculus were inconsistently present. Megabacteria (approximately 40-50 by 2-4 microns, gram-positive to gram-labile, rod-shaped organisms) were present in large numbers in touch preparations of the proventricular mucosal surface. In some of the preparations, the megabacteria showed a branching pattern similar to fungal hyphae. By histopathology, all birds showed moderate to marked, diffuse lympho-plasmacytic proventriculitis. Heterophilic exudation was present in the terminal portion of the proventriculus, where the greatest numbers of the organism were found. Megabacteria were present in the mucus covering the mucosal surface and the lumina of the superficial proventricular crypts, occasionally invading the luminal epithelium. Megabacterial infection was in general associated with other diseases such as avian tuberculosis, salmonellosis, coccidiosis, chlamydiosis and various other bacterial and parasitic infections. Only in one hen no other concurrent infectious organism was detected. The turkey had histomoniasis. Wild birds were regarded as probable source of infection, since all affected birds were kept under conditions allowing contact to wild birds and we have diagnosed megabacterial infections in wild-living green finches earlier.

A comparative study of the pathogenesis of malabsorption syndrome in broilers

Five malabsorption syndrome (MAS) homogenates from The Netherlands and Germany were used to reproduce MAS in broilers. We studied the histopathology after inoculation of 1-day-old broiler chicks and the agents that might be involved. Generally, the MAS homogenates induced signs that differed in severity and pathobiology. We could distinguish and classify the inoculated groups best by histopathology: proventriculitis, lesions in the small intestines in combination with proventriculitis, or lesions of the small intestines only. Lesions in the small intestine had more impact on weight gain depression than lesions in the proventriculus. In three out of five inoculated groups, microscopic lesions of the pancreas were found. Reovirus was detected in the inoculated groups by virus isolation and seroconversion, and reoviral antigen was detected by immunohistochemistry of the small intestine. Also, enteroviruslike particles were detected in three of the five inoculated groups, although not in the most affected group. Additionally, bacteriophages and bacteria (hemolytic Escherichia coli, Pasteurella hemolytica, and Enterococcus durans) were isolated from inoculated chicks. The role these agents play in pathogenesis of MAS is still unsolved.

[Proventriculitis in domestic fowl (Gallus gallus var. dom. L., 1758) caused by megabacteria]

Three cases of a disease similar to going light syndrome in budgerigars in a flock of young laying hens in Turkey are reported. In all cases megabacteria in association with E. coli could be isolated. The causing agent appeared to be large, rod-shaped, gram-positive or gram-labil, and catalase test positive bacteria with cytochromoxydase activity. Subcultivation of these bacteria could not be achieved.

Role of the Yersinia pestis hemin storage (hms) locus in the transmission of plague by fleas

Yersinia pestis, the cause of bubonic plague, is transmitted by the bites of infected fleas. Biological transmission of plague depends on blockage of the foregut of the flea by a mass of plague bacilli. Blockage was found to be dependent on the hemin storage (hms) locus. Yersinia pestis hms mutants established long-term infection of the flea's midgut but failed to colonize the proventriculus, the site in the foregut where blockage normally develops. Thus, the hms locus markedly alters the course of Y. pestis infection in its insect vector, leading to a change in blood-feeding behavior and to efficient transmission of plague.

Catarrhal proventriculitis associated with a filamentous organism in pet birds

Catarrhal proventriculitis due to infection by an unidentified organism was diagnosed in 79 of 534 pet birds examined histologically. It was more prevalent in domestic birds (70 cases) than in imported ones (9 cases). A high incidence of the disease was encountered in budgerigars (Melopsittacus undulatus) and it was occasionally found in finches (Poephila gouldiae gouldiae), parakeets (Psittacula Krameri manillensis), Amazona parrots (Amazona aestiva aestiva) and cockatiels (Nymphicus hollandicus). The agent was a large filamentous rod, and was stained positively with Gram, GMS and PAS methods. Histologically, it induced a mild to moderate exudative or proliferative inflammation in the proventriculus. All the cases had an erosion in the gizzard. Ultrastructurally, the organism had a eukaryotic nucleus and three cell-wall layers. Concurrent infections were very common, including adenoviruses (37 cases), giardiasis (31 cases), candidiasis (13 cases), papovaviruses (11 cases) and knemidocoptic mites (11 cases).

Megabacteriosis in exhibition budgerigars

Megabacteriosis is a common cause of illness and death in exhibition budgerigars. The clinical signs are variable but include weight loss, difficulty in swallowing, vomiting, diarrhoea and sudden death due to haemorrhage. Significant lesions are confined to the proventriculus which becomes inflamed, dilated and ulcerated, and loses its normal architecture, and to the gizzard in which there are degenerative changes in the koilin layer.

The pathogenesis of velogenic Newcastle disease virus infection of chickens of different ages and different levels of immunity

Chickens of 7 weeks or 20 weeks of age were divided into three groups according to their antibody status (high, low, absent) and were infected with a velogenic viscerotropic Newcastle disease virus. To follow patterns of viral replication, birds were necropsied at regular intervals up to 22 days and organs were sampled from each bird. In non-immune birds, virus could be isolated from all organs examined. In birds with antibody, virus was most frequently isolated from the proventriculus, cecal tonsil, bursa, and brain. However, because no one organ could be recommended for all situations, all four should be sampled for field diagnosis. In immune birds, although clinical signs were either mild or absent, widespread virus replication occurred up to 19 days post-challenge.

Characterization of a gram-positive bacterium from the proventriculus of budgerigars (Melopsittacus undulatus)

The cellular, cultural, and biochemical characteristics of eight isolates of a large gram-positive bacillus that are commonly observed as apparently normal flora in the proventriculus of budgerigars (Melopsittacus undulatus) were determined. The bacterium was highly pleomorphic and changed markedly in both diameter and length when subcultured on agar media. The bacterium was facultative anaerobic and capnophilic, hemolytic on blood agar, and formed flat colonies with irregular edges after incubation for several days. All isolates grew on sodium azide agar but did not grow on MacConkey agar. The isolates were catalase-negative and oxidase-negative and did not reduce nitrate. All isolates failed to utilize arginine, lysine, ornithine or tryptophane but produced acid from glucose, galactose, levulose, maltose, melibiose, starch, and sucrose. All isolates produced acetoin from glucose and hydrolyzed esculin. The eight isolates could not be identified to either genus or species level based on the descriptions of currently classified organisms in the division Firmicutes as described in Bergey's Manual of Systematic Bacteriology.

Histamine distribution in the gastrointestinal wall of germ free and conventional chicken: evidence of the role of the digestive microflora

The digestive microflora produces a decrease of the mucosal histamine content in the wall of the chicken colon but has no significant incidence in the upper part of the digestive tract. The anatomical and physiological particularities of the chicken digestive tract permitted to observe that wall histamine concentration depends on different factors. Endogenous factors control the wall histamine content in the proventriculus, independantly of the diet and/or of the presence of a microflora. Diet has a specific incidence upon the gastrointestinal wall of the host in the crop and in the colon. The colon microflora decreases the effect of the diet essentially when the chicken are fed a semi synthetic diet. Interactions between the diet and the microflora could induce physiopathological manifestations.

Haematological findings in budgerigars with megabacterium and Trichomonas infections associated with 'going light'

Eighteen budgerigars with clinical signs of 'going light' were euthanased and examined post mortem; ingluvitis caused by Trichomonas gallinae infection was present in seven birds, proventriculitis associated with the presence of megabacteria in eight birds and in three birds both conditions were present. Haematological examinations of blood taken from the living birds showed that those with T gallinae infection had normal white cell counts whereas those in which megabacteria were present had significant leucocytosis and heterophilia. Some birds in both groups were anaemic. The findings suggest that infection with megabacteria may be responsible for a proportion of cases of 'going light' in budgerigars and that haematological examination can establish this diagnosis in living birds.

Delayed replication of Marek's disease virus following in ovo inoculation during late stages of embryonal development

Several oncogenic and non-oncogenic isolates of Marek's disease virus (MDV) were inoculated into embryonated eggs on embryonation day (ED) 16 to 18, and embryos or chicks hatching from inoculated eggs were examined for infectious virus and viral internal antigen (VIA) in lymphoid organs. There was no evidence of extensive replication of MDV in any of the embryonic tissues examined. Levels of VIA peaked 4-5 days after chicks hatched. This indicated that MDV remained inactive during embryonation and did not initiate pathogenic events until chicks hatched. Because HVT replicated rapidly in the embryo but MDV did not, in ovo inoculation of HVT simultaneously with oncogenic MDV or several days after MDV resulted in significant protection (P less than 0.025) of hatched chicks against Marek's disease (MD). Little protection was obtained if HVT was given simultaneously with MDV or after MDV to chicks already hatched. The relative susceptibility of the embryo to extensive replication of the vaccine virus but not the challenge virus apparently accounted for protection against MD in chicks hatching from dually infected eggs.

Colonization of Lactobacillus acidophilus in gnotobiotic chicks

Germ-free chicks hatched in flexible film gnotobiotic isolators were dosed orally at 2 days of age with a pure culture of Lactobacillus acidophilus. The chicks monoassociated with L. acidophilus were killed at 2 weeks of age to obtain gastrointestinal tract specimens for histological sectioning. Both light microscopy and transmission electron microscopy were performed to determine colonization and adhesion of lactobacilli. This strain of L. acidophilus was found associated with epithelium from three segments of the gastrointestinal tract (crop, proventriculus, and duodenum) of the gnotobiotic chick. The electron micrographs showed not only a close relationship between the Lactobacillus organism and the crop epithelia, but also an attachment through physical contact.