Phylogenetic analysis of low-pathogenicity avian influenza H6N2 viruses from chicken outbreaks (2001-2005) suggest that they are reassortants of historic ostrich low-pathogenicity avian influenza H9N2 and H6N8 viruses.

Low-pathogenicity (LPAI) and high-pathogenicity (HPAI) avian influenza viruses are periodically isolated from South African ostriches, but during 2002 the first recorded outbreak of LPAI (H6N2) in South African chickens occurred on commercial farms in the Camperdown area of KwaZulu/Natal (KZN) Province. Sequence analysis of all eight genes were performed and phylogenetic analysis was done based on the hemagglutinin and neuraminidasc sequences. Results from phylogenetic analyses indicated that the H6N2 chicken viruses most likely arose from a reassortment between two South African LPAI ostrich isolates: an H9N2 virus isolated in 1995 and an H6N8 virus isolated in 1998. Two cocirculating sublineages of H6N2 viruses were detected, both sharing a recent common ancestor. One of these sublineages was restricted to the KZN province. The neuraminidase gene contained a 22-amino acid deletion in the NA-stalk region, which is associated with adaptation to growth in chickens, whereas the other group, although lacking the NA-stalk deletion, spread to commercial farms in other provinces. The persistence of particular H6N2 types in some regions for at least 2 yr supports reports from Asia and southern California suggesting that H6N2 viruses can form stable lineages in chickens. It is probable that the ostrich H6N8 and H9N2 progenitors of the chicken H6N2 viruses were introduced to ostriches by wild birds. Ostriches, in which AI infections are often subclinical, may serve as mixing vessels for LPAI strains that occasionally spill over into other poultry.

Phenotypic and molecular characterization of V-factor (NAD)-independent haemophilus paragallinarum.

In South Africa from early 1989 onward, strains of Haemophilus paragallinarum not requiring nicotinamide adenine dinucleotide (NAD) have been isolated from commercial chickens suffering from infectious coryza. Fifteen of these field isolates were characterized by biochemical typing, serotyping, restriction endonuclease analysis (REA), and ribotyping. The chosen isolates represented diversity in geographic location, time of disease outbreak, and type of flock. All were typical of the species in biochemical properties, except that they were NAD-independent, and all were Page serovar A. REA was performed with three enzymes: HindIII, HpaII, and SspI. All isolates gave identical REA profiles with all three enzymes. Ribotyping was performed using a probe that consisted of the plasmid pUC19 into which the 16S rRNA operon of H. paragallinarum had been inserted. All 15 isolates gave the same ribotyping profile using each of the three enzymes. As a group, the NAD-independent strains gave REA profiles and ribotypes that were very different from a range of classic South African strains isolated before 1989. Our results strongly suggest that the NAD-independent isolates are clonal in nature.

Characterization of a pigeon paramyxovirus (PPMV-1) isolated from chickens in South Africa.

A paramyxovirus with a thermostability of 60 min (typical of velogenic viruses) and a mean death time of > 90 h (typical of lentogenic viruses) was isolated from layers near Mooi River, South Africa. Our results, based on comparative nucleotide sequence data indicated that the virus is pigeon paramyxovirus 1 (PPMV-1), a variant of Newcastle disease virus. The F0 cleavage site contains a 112RRKKRF117 motif, and the virus had 98% sequence identity with PPMV-1 strains from the Far East. PPMV-1 was last reported in South Africa during the 1980s, with this being the first report of PPMV-1 isolated from chickens in South Africa.

Confirmation that PCR can be used to identify NAD-dependent and NAD-independent Haemophilus paragallinarum isolates.

Seventy five bacteria tentatively identified as Haemophilus paragallinarum (the causative agent of infectious coryza), eight identified as Ornithobacterium rhinotracheale and 13 identified as NAD-independent Pasteurella species were isolated from chickens with respiratory infection in various provinces in South Africa. The isolates were characterized by conventional biochemical and serological methods. A polymerase chain reaction (PCR) assay specific for H. paragallinarum was used to identify the cultures directly from colonies. The PCR assay gave positive results for all isolates that were identified by conventional methods as H. paragallinarum, irrespective of whether they were nicotinamide adenine dinucleotide (NAD)-dependent (43 isolates) or NAD-independent (32 isolates). The eight isolates that were identified by conventional methods as O. rhinotracheale and the 13 isolates identified as various Pasteurella species gave negative results in the PCR assay. This study has demonstrated that colony PCR is a rapid method for uniquely identifying both NAD-dependent and NAD-independent strains of H. paragallinarum and distinguishing them from other bacteria, such as O. rhinotracheale and Pasteurella species.

Suspected ammonium nitrate fertiliser poisoning in cattle.

The occurrence of a suspected mixed ammonia and nitrate fertiliser poisoning that led to acute illness and fatalities in cattle is described. The circumstances leading to the incident included the method of application of the fertiliser, low rainfall and the absence of subsequent irrigation of the fertilised pastures. The clinical and gross post mortem findings, principally dehydration and fluid distension of the rumen, were not pathognomonic. The complex of nitrate, nitrite and ammonia toxicity is discussed.

Poxvirus in farmed Nile crocodiles.

In an outbreak of wart-like skin lesions in nine-month-old farmed Nile crocodiles (Crocodylus niloticus) the lesions were especially common on the head and neck but occurred on all parts of the body except the tail. Eosinophilic intracytoplasmic inclusion bodies were present in epithelial cells and further examination of the lesions by transmission electron microscopy revealed the presence of a poxvirus. An autogenous vaccine was produced from material from the lesions and in six vaccinated crocodiles the lesions healed more quickly than in unvaccinated controls.

Dermatophilus congolensis infection in cattle.

The history, appearance and clinical course of a low incidence, chronic skin disease in beef cattle is reported. Calves were affected from 3 months of age and the condition persisted into adulthood. The infection was caused by Dermatophilus congolensis and resulted in severe crusting of the skin. Sheep were kept on the farm until 4 years ago. The method of diagnosis is discussed.

Isolation and identification of psittacid herpesvirus 1 from imported psittacines in South Africa.

Acute deaths occurred in 47 out of a total of 131 imported psittacine birds whilst in quarantine. Few and non-specific clinical signs were seen during the course of the disease outbreak, but gross pathology revealed severe hepatomegaly and splenomegaly. A herpes virus was isolated from liver and spleen material taken from 2 birds, an Amazon (Amazona aestiva aestiva) and a Yellow-collared macaw (Ara auricollis). Identification procedures included virus neutralisation tests carried out in chicken embryo fibroblast cultures. Neutralisation of the virus was obtained by antisera to Psittacid herpesvirus type 1 (HV1) but not against HV2 or HV3.

An upper respiratory disease of commercial chickens resembling infectious coryza, but caused by a V factor-independent bacterium.

From early 1989 the emergence of an infectious bacterial disease resembling infectious coryza was seen in several commercial chicken flocks in Natal Province of South Africa. Clinical signs were facial swelling and nasal discharge. An organism was routinely isolated from the infra-orbital sinus or trachea of infected chickens. The organism was found to be a Gram-negative rod, non-motile, V factor (nicotinamide adenine dinucleotide, NAD)-independent, catalase negative, oxidase positive and urease and indole negative. No gas was produced from carbohydrates and acid was produced from glucose, mannitol, inositol and sorbitol. Experimental inoculation of this organism into the infraorbital sinus of SPF chickens and conventional broilers produced an acute upper respiratory disease. The organism could be recovered for up to 7 days post-inoculation. The organism is closely related to Haemophilus paragallinarum, the cause of infectious coryza, but because it is NAD-independent it cannot be classed as an Haemophilus species.

NAD (V-factor)-independent and typical Haemophilus paragallinarum infection in commercial chickens: a five year field study.

An unusual bacterium causing respiratory disease in chickens emerged in South Africa in February 1989. The disease resembled infectious coryza but the organism differed from typical Haemophilus paragallinarum especially in that it did not require V-factor for growth. It has been termed an NAD-independent H. paragallinarum. A study of avian haemophili isolated from diseased chickens in Kwazulu-Natal over the past five years revealed the presence of typical H. paragallinarum, NAD-independent H. paragallinarum and H. avium (now transferred to the genus Pasteurella). Before the end of 1989 the NAD-independent H. paragallinarum had become the predominate isolate and thereafter was isolated from commercial chickens in other regions of South Africa. The disease affected all strains of chickens in an overall age range of 14 days to 64 weeks. The organism was responsible for upper respiratory disease of broilers and layers and implicated in lower respiratory disease of broilers. It was commonly isolated from diseased adult birds previously vaccinated against typical H. paragallinarum. Broilers were most commonly infected from 3 weeks of age and layers within the placement to peak production period. Whole cell protein profiles of NAD-independent H. paragallinarum isolates from five different commercial poultry units were identical but differed from that of a typical isolate.

A phylogenetic study of South African Newcastle disease virus strains isolated between 1990 and 2002 suggests epidemiological origins in the Far East.

Genetic comparisons were made of the fusion protein sequences of 155 Newcastle disease virus isolates collected in South Africa between 1990 and 2002. Their evolutionary relationships and origins are described. All of the lentogenic field isolates were shown to be derived from commercial vaccines. No true South African lentogenic wild type strain was identified. Furthermore, it was shown that almost all mesogenic isolates had avirulent F(0) cleavage site sequences. Three major epizootics occurred in South Africa during the period of this study. The first outbreak (1990/1991) was caused by viruses endemic to South Africa since the 1960's (genotype VIII) but were occasionally also isolated in 2000. Genotype VIIb viruses, implicated in the severe outbreaks during 1993/1994, persisted until 1999. Genotype VIId viruses, responsible for the most recent outbreak in 1999/2000, had their origins in the Far East like those of the two previous outbreaks.