Molecular epidemiology of two fowl cholera outbreaks on a free-range chicken layer farm.

Two outbreaks of fowl cholera on a multiage free-range egg farm were investigated. The outbreaks occurred in 1994 and 2002. A total of 22 strains of Pasteurella multocida were available for study, 11 from the 1994 outbreak and 11 from the 2002 outbreak. Lesions typical of acute fowl cholera were seen in the 1994 outbreak, whereas both acute and chronic fowl cholera occurred in the 2002 outbreak. The isolates were examined in an extended phenotypic typing methodology, by a P. multocida-specific polymerase chain reaction (PCR), by the Heddleston somatic serotyping scheme, and by restriction endonuclease analysis (REA) typing using the enzyme HpaII. All 22 strains had the same phenotypic properties, all were confirmed as P. multocida by PCR, all were Heddleston serovar 4, and all had the same REA pattern. The results indicate that these 2 outbreaks were caused by the same clone of P. multocida--despite the 8-year time period between the outbreaks.

Amoxycillin as an alternative to dihydrostreptomycin sulphate for treating cattle infected with Leptospira borgpetersenii serovar hardjo.

OBJECTIVE: To assess the effect of amoxycillin treatment on urinary excretion of leptospires from cattle infected with Leptospira borgpetersenii serovar hardjo. DESIGN: A chemotherapy trial with controls. PROCEDURE: Fourteen heifers serologically negative to L hardjo were inoculated with L hardjo via the conjunctival route and assessed for evidence of infection by serological, fluorescent antibody and microbiological tests. Two injections (48 h apart) of amoxycillin at a dose of 15 mg/kg were administered intramuscularly to seven heifers 6.5 weeks after infection; the remaining heifers acted as untreated controls. Later, these seven control group heifers were treated with a single dose of amoxycillin (15 mg/kg). Samples of urine were collected before and after amoxycillin treatments; kidneys were collected at slaughter, and examined by fluorescent antibody test and microbiological culture. RESULTS: Leptospires were isolated from the urine of 11 of 14 heifers inoculated with L hardjo. After treatment of six of these with two injections of amoxycillin, leptospires were not isolated. Of the controls, four of the five initially leptospiruric heifers continued to shed leptospires; after a single injection of amoxycillin, no leptospires were detected in the kidneys of these four. CONCLUSION: Amoxycillin may be an acceptable alternative to dihydrostreptomycin sulphate for the treatment of cattle infected with L hardjo.

Experimental Leptospira borgpetersenii serovar hardjo infection of pregnant cattle.

OBJECTIVE: To observe the effect upon the foetus of experimental infection of pregnant cattle with Leptospira borgpetersenii serovar hardjo. DESIGN: A disease transmission study using pregnant cattle. PROCEDURE: Fourteen heifers serologically negative to L hardjo were artificially inseminated and later challenged with a north-Queensland isolate of L hardjo by conjunctival inoculation. The heifers were serologically monitored and their urine examined for the presence of leptospires using culture and fluorescent-antibody tests at appropriate intervals. Elective caesarean sections were performed on pregnant heifers at 6.5 weeks after the challenge. Foetuses were examined using serological, histopathological, microbiological and fluorescent-antibody tests. RESULTS: Ten of the heifers became pregnant, but three subsequently aborted before challenge. After challenge, all 14 heifers seroconverted and L hardjo was isolated from the urine of 6 of the 7 pregnant heifers. No evidence of foetal L hardjo infection was detected. Two of the foetuses had histopatho-logical lesions consistent with Neospora sp infection. CONCLUSION: It is likely that the isolate of L hardjo used in this study does not normally infect the foetus. Neospora sp may be a more significant cause of bovine reproductive wastage.

Lesions of experimental equine morbillivirus pneumonia in horses.

Laboratory examinations of equine morbillivirus included experimental reproductions of the disease caused by the virus by transmission of mixed lung and spleen taken from two field equine cases into two horses and by inoculating tissue culture virus into a further two horses. The most distinctive gross lesions of the diseases that developed in three of the horses was that of pulmonary edema characterized by gelatinous distension of subpleural lymphatics. Histologically, the lesions in the lungs were those of serofibrinous alveolar edema, alveolar macrophages, hemorrhage, thrombosis of capillaries, and syncytial cells. Clearly defined vascular lesions in three horses that became clinically affected within 8 days of inoculation of virus included intramural hemorrhage, edema, and necrosis and syncytial cells in the endothelium of pulmonary vessels (approximately 40-70 microm in diameter). Vascular lesions accompanied by parenchymal degeneration were also seen in the heart, kidney, brain, spleen, lymph node, and stomach. A fourth horse, which survived for 12 days, had detectable lesions only in the lungs, which were more chronic than those in the other three horses, a greater degree of cellular infiltration, and fewer well-defined vascular lesions. Sections stained by an indirect immunocytochemical method showed equine morbillivirus antigen was present in the vascular lesions and along alveolar walls. When endothelial cells were examined by electron microscope, cytoplasmic virus inclusion bodies containing filamentous structures were seen that reacted to an immunogold test to equine morbillivirus antigen. The presence of the syncytia in the small blood vessels in the lungs and other organs was interpreted as an important characteristic of the disease and consistent with a reaction to a morbillivirus.

A review of laboratory techniques and their use in the diagnosis of Leptospira interrogans serovar hardjo infection in cattle.

This paper reviews the laboratory diagnosis of Leptospira hardjo infection in cattle. Two genotypes of L hardjo, Hardjoprajitno and Hardjobovis, have been identified in cattle, but only Hardjobovis has been isolated in Australia. There are problems with diagnosis and control of bovine leptospirosis. Infection is usually subclinical and the serological titres vary greatly in peak and duration. Leptospires may be excreted in urine for up to 18 months. Low microscopic agglutination test titres may be significant in unvaccinated herds as indicators of endemic infection. Vaccines differ in their composition, and their efficacy is difficult to evaluate. The serological response after vaccination is difficult to differentiate from the response after infection. Pregnant cows that become infected may abort, but this is usually after the serological response has peaked. Therefore, paired serum samples are of little use in diagnosing abortion caused by L hardjo. Fluorescent antibody techniques are more sensitive than dark field microscopy for detection of leptospires in urine and tissue samples. Techniques for culture have improved but are still difficult to perform and take 3 months or longer for results to be known. DNA probes and polymerase chain reaction tests are very sensitive and specific, quick to perform, and can be used on fluid and tissue samples.

Suspected botulism in three intensively managed Australian cattle herds.

Serious outbreaks of a paralytic disease in cattle occurring in the spring and summer of 1988 were investigated on three farms in south eastern Queensland, Australia. On one farm 237 (31 per cent) of 770 cattle died, on the second 109 (40 per cent) of 271 cattle died and on the third 30 (8 per cent) of 380 cows died. Botulism was suspected on the basis of the clinical signs, the lack of significant pathology, a failure to incriminate other agents and a positive feeding trial in one sheep. Laboratory tests for the presence of botulinum toxin failed to confirm this diagnosis, and further feeding trials using ingredients of two rations were also negative.

Rhinocerebral and nasal zygomycosis in sheep caused by Conidiobolus incongruus.

The clinical findings, pathology and mycology of a cluster of 5 ovine cases of rhinocerebral and nasal zygomycosis caused by Conidiobolus incongruus are described. All cases were in Border Leicester or Merino x Border Leicester ewes from a flock pastured in a low-lying paddock adjoining a small tidal river in subtropical Queensland (latitude 28 degrees S). These cases of zygomycosis are believed to be the first infections due to C incongruus recorded in animals other than humans. The disease was subacute in 4 animals with a course of up to several weeks. In these, the primary site of infection was the posterior nasal cavity. The lesions extended to the dorsum of the face between the eyes, to the orbital cavity and to the anterior brain and meninges in the cranial cavity. In one animal, where the anterior nasal cavity was affected and iodine treatment used, the course was longer. The fungal granulomas had numerous foreign body giant cells, neutrophils and eosinophils. Fungal hyphae were thin walled, 6 to 8 microns in diameter, with occasional septa and irregular branching. They were cuffed with a wide zone of necrotic cell coagulum, or with homogeneous eosinophilic Splendore-Hoeppli granules.

Disease of geese caused by a new herpesvirus.

A goose flock farmed outdoors in south-eastern Queensland suffered an outbreak of peracute disease with high death rate (97%). Small button ulcers and large plaques overlying lymphocyte aggregates were present on the mucosa of the small intestine of affected birds. Small white foci of necrosis and focal haemorrhages were seen in the livers. Numerous intranuclear inclusion bodies were observed microscopically in hepatocytes and a herpesvirus which grew rapidly in chicken kidney cells was isolated from tissues. Duck virus enteritis (DVE) was suspected but DVE antiserums failed to neutralise the virus. Further serological studies with a limited range of known avian herpesviruses have failed to identify the virus. Experimental transmission resulted in high mortality in geese (100%), lower mortality in ducklings and nil mortality in chickens. Surveillance studies showed no evidence of infection in domestic and wild birds beyond the original farm and the infection appears not to have been established in the area. Wild ducks, which were frequent visitors to the farm dam, were considered the most likely source of the infection.

An evaluation of three serological tests for antibody to Brucella suis in pigs.

The Rose Bengal Plate Agglutination test (RBT), the complement fixation text (CFT) and the tube agglutination test (TAT) were applied to serums from 345 feral and 80 domestic pigs sampled at slaughter. At least 2 of the 3 serological tests were applied to each serum. Tissues from all pigs were cultured for Brucella suis and the degree of culture effort was categorised from 1 to 4 in decreasing order. Fifty-eight feral and 35 domestic pigs were culture-positive. A greater proportion of culture-positive pigs was obtained for category 1 and 2 culture effort. Tissues yielding B. suis most often were mandibular, gastrohepatic and external iliac lymph nodes, spleen and various abdominal organs. Infection in domestic pigs was associated with exposure to feral pigs. The sensitivity (Se) in culture-positive pigs of the RBT (79.1%) was significantly greater than that of either the CFT (49.1%) or TAT (51.1%). The specificities (Sp) in culture-negative pigs were 81.2% for the RBT, 90.8% for the CFT and 81.0% for the TAT. A more realistic estimate of Sp for the RBT was considered to be 97.6%, based on serological results from 31,326 domestic pigs routinely tested for regulatory purposes. The RBT was clearly superior to the other 2 tests in this study. However, a more sensitive screening test would be preferable for use in a test and slaughter eradication program. The RBT would be a suitable confirmatory test.

Melioidosis in intensive piggeries in south eastern Queensland.

The epidemiology of melioidosis was investigated in 8 intensive piggery units which used water from the same river in south eastern Queensland. In 3 consecutive years cases of disease followed heavy rainfall and flooding. Although Pseudomonas pseudomallei was not isolated from water or soil samples the water supply was suspected as the source of infection. Affected pigs were detected at slaughter by the presence of abscesses most commonly in the bronchial lymph nodes (40%) and spleen (34%). One hundred and fifty nine cases were observed at slaughter from a total of 17,397 animals at risk. Infection by inhalation of water aerosols derived from nipple drinkers, hose sprays and a water misting cooler was considered to be responsible for the bronchial lymph node lesions. These outbreaks occurred outside the area in which melioidosis is generally regarded as being endemic.

Field cases of aflatoxicosis in pigs.

Five cases of aflatoxicosis in pigs in southern Queensland are described. One peracute case where aflatoxin concentrations of up to 5000 micrograms aflatoxin B1/kg were demonstrated in stomach contents was presumed to be caused by consumption of mouldy bread. High levels of toxins were also present in the livers. Two cases of acute toxicity were caused by feeding mouldy peanut screenings containing 22000 micrograms aflatoxin B1/kg. One case of subacute and one of chronic toxicity were caused by sorghum grain based rations with lower aflatoxin levels (4640 and 255 micrograms/kg). Peracute toxicity caused collapse and deaths within several hours, acute toxicity caused deaths within 12 h and with subacute toxicity deaths occurred after 3 weeks on a toxic ration. Anorexia and ill thrift affecting only growing animals were seen with chronic toxicity. Extensive centrilobular liver necrosis and haemorrhage occurred with peracute toxicity and in cases of acute poisoning there was hepatic centrilobular cellular infiltration, hepatocyte swelling and bile stasis. With subacute toxicity hepatocyte vacuolation together with bile stasis and bile ductule hyperplasia were seen.

Pathology and tuberculin sensitivity in cattle inoculated with Mycobacterium avium complex serotypes 6, 14 and 18.

Three strains of Mycobacterium avium complex organisms, serotypes 6, 14 and 18 isolated from typical tuberculous lesions in cattle were examined for pathogenicity and ability to sensitise cattle to avian and bovine tuberculin. Each strain caused tuberculoid granulomas at the site of subcutaneous inoculation but no lesions elsewhere. Sensitisation to bovine tuberculin was detected in the caudal fold test in 11 of 18 inoculated animals 8 weeks after injection. In a simultaneous comparative cervical test, reactions to avian tuberculin were much larger than reactions to bovine tuberculin in all inoculated animals.