Megabacteria in Budgerigars

Introduction

Megabacteriosis is a common cause of morbidity and mortality in British exhibition Budgerigars. This is caused by a large organism, the so-called Megabacteria, which forms a mat within the proventriculus of affected Budgerigars. This leads to a chronic debilitating condition.

Initially there is a subclinical carrier state, which then leads to a chronic proventriculitis and proventricular enlargement. Secondary changes can also occur in the liver due to anorexia Clinical signs vary and can include vomiting, passing of whole seeds and emaciation. Infection is widespread and it is assumed that the main route of distribution is the purchase of infected birds into an exhibition stud.

Treatment is possible with oral amphotericin, classically considered an antifungal drug. Problems can occur with treatment as this drug has poor systemic uptake and many birds are unable to recover clinically due to the proventricular damage. Diagnosis of infection is best performed at post mortem. Grossly there is an enlarged proventriculus and possible liver changes. In early cases this may be difficult to detect. Gram stained slides of deep smears from the proventricular mucosa, reveal the large Gram positive rods - the Megabacteria. Histo-pathologically there is a chronic proventriculitis and Megabacteria can be seen in the sections. In some cases the Megabacteria have been identified in impression smears of the liver and spleen. The proventricular changes have also been identified in birds that have been treated and are clear of the Megabacteria but failed to respond clinically. This is now termed Megabacteria Associated Disease (M.A.D.). This can lead to emaciation and death in the absence of the Megabacteria. A study of the disease in a British exhibition stud was undertaken and control measures implemented to limit the spread, or eliminate the disease. Selection and culling of affected birds alone does not appear to reduce incidence.

Material and Methods

The stud comprises of a fluctuating adult population of two hundred birds with around three hundred chicks being reared each season between October and May. Birds are exhibited between June and September. The stud is not closed with a few birds being introduced each year. Surplus birds are sold throughout the year. Megabacteria were first identified in the stud by proventricular smears and histo-pathology in February 1996. No secondary disease processes were identified in infected individuals by gross post mortem, culture of proventricular swabs or histo-pathology throughout this initial investigation. Birds were given presumptive treatment with amphotericin by crop tube twice daily for ten days. Many cases failed to respond and were subjected to post mortem examination. Histo-pathology and Gram stained smears of the proventriculus showed there was no Megabacteria but the birds were suffering from a chronic proventriculitis that would be compatible with such an infection. These birds were suffering from Megabacteria associated disease.

Currently two forms of amphotericin are being used in the UK to treat this condition

1. "Fungilin" (Squibb) amphotericin solution 100mg/ml. Dosage regimes vary from 0.05 to 0.3ml twice daily by crop tube exactly twelve hours apart for ten days. Problems arise with this as this regime is poorly tolerated by the birds and individuals may regurgitate the drug. Water and food consumption is depressed. It is also practically difficult for a fancier to administer to large numbers of birds.
2. "Megabac-S" (Vetrepharm) amphotericin powder. This is given at the rate of 250mg per 50ml distilled water for ten days. It must be given in ultra-violet protected drinkers and birds must consume 4ml/100g-body weight a day to get a therapeutic dose. Although easy to use some birds fail to drink sufficient to get a therapeutic dosage. In order to monitor intake the birds need to be individually housed. If intake is low the bird needs to be given the remaining dose via a crop tube. The use of this formulation in drinking water has been shown to reduce incidence but not eliminate the disease. In the UK a special treatment authorisation from the Veterinary Medicines Directorate is required to obtain this drug legally. Neither of these formulations is absorbed systemically and neither will prevent the ongoing proventricular damage (M.A.D.).

As a result of these factors all birds were critically assessed before treatment. Birds had to be well fleshed with rounded pectoral muscles and healthy. Candidates for treatment were identified by clinical examination. Any, which failed these criteria, were rejected form the trial and were removed from the premises. Birds were isolated in metal cages in groups of two in a building which never previously housed budgerigars. This building was power-washed and disinfected out using "Virkon" a virucidal, fungicidal and bacteriocidal agent. The birds were treated with "Fungilin" by crop tube 0.1ml twice a day and "Megabac-s" in distilled water (250mg/50ml) as the sole source of water for ten days. Between doses the crop tubes and syringes were washed in distilled water and subjected to cold sterilisation in "Gygasept". The crop tube was wiped clean between birds to reduce contamination from bird to bird. These birds were kept in isolation from the infected stock and the persons involved in treatment wore specific clothing before entering the treatment area. Hands were scrubbed in chlorhexidine and shoes were dipped in a footbath of "Virkon".

After five days of treatment the bird's cages were cleaned out thoroughly to reduce the environmental contamination. On the tenth day the birds were again subjected to a critical clinical examination and transferred into inside flights in their batches. This was within the same building but a different person was responsible for the management of the birds and they were in a different section, so there was no direct contact. Any birds, which died during treatment or failed to pass the clinical examination at the end of treatment were euthanased and subjected to post mortem. Between batches the entire area was again power-washed and disinfected as before. Once the original housing was empty of birds, these were cleaned out, power-washed and disinfected as before. Once finished all birds were transferred back into the original housing. Any deaths or birds that were euthanased were subjected to post mortem examination.

All purchased birds were subjected to the treatment protocol as above, individually. Once finished they were housed individually in cages before release into the stud. If any bird failed on clinical examination then it did not enter the stud and was euthanased. All deaths or euthanased birds in this group were subjected to post mortem examination. Exhibition birds were also considered a possible risk of re-infection so these birds were housed in separate cages and treated with "Megabac-S" as previously described.

Results

In total, two hundred and twenty-one birds were treated with this regime between the first of January and the eighteenth of June 1997. Two hundred and fourteen birds completed treatment. A variety of clinical conditions were identified in the seventy-five birds examined at post mortem. This was carried out over two years after the start of treatment, including offspring from the treated birds. Five birds had signs of Megabacteria associated disease, showing dilated proventriculi with chronic proventriculitis on histopathology but both smears and the histology failed to identify any Megabacteria present.

Discussion

A diagnosis of Megabacteriosis can be made by mucosal smears of the proventriculus or histopathological examination of the proventriculus. A clinical diagnosis in the live bird is difficult and the only test available is that of faecal examination, however this may give false negative results. Treatment in the live bird is essentially the use of amphotericin 100mg/ml (Fungilin, Squibb) by crop tube 0.1ml twice daily for ten days, but this is poorly tolerated and many birds regurgitate the drug. More recently the use of water-soluble amphotericin 250mg/50ml distilled water (Megabac-S, Vetrafarm) has been used. In many cases treatment is unsuccessful due to systemic infection or the subsequent chronic proventriculitis, the Megabacteria associated disease. Many budgerigars will also fail to drink sufficient of the solution to achieve a therapeutic level and water intake needs to be monitored. Birds can then be caught and dosed by crop tube to the correct amount, 6ml of solution per 100g body weight.

Prevention of Megabacteriosis by culling of heavily infected birds and careful selection of the birds used for breeding may not decrease the levels in the offspring and this may be due to a high percentage of clinically healthy budgerigars carrying the organism. The use of amphotericin in the water does reduce incidence but is unlikely to eliminate Megabacteriosis due to the reasons mentioned above. This is why a combination therapy of both types of oral amphotericin was used in this case. From a personal point of view, clinical assessment of stock is needed to ensure that they are ideal candidates for treatment. This means that any sick bird or underweight bird, which may be suffering from irreversible proventriculitis or a possible candidate for a systemic infection should not be treated. Isolation before, during and after treatment is essential.

I feel it is important to ensure that free status is maintained by the routine treatment of all bought in purchases, which should undergo the same screening process. Scrupulous attention to hygiene cannot be stressed enough.

Original text Copyright 1999, Kevin Eatwell BVSc (hons) MRCVS .

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