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sion dam (Stanley 1979). Most of the species collected in the bait traps were those associated with permanent and semipermanent fresh water breeding sites, and the dominant species was Culex annulirostris, which accounted for over 70 per cent of the collections (Liehne et al. 1976a; Stanley 1979). Thus the major vector species for MVE virus was shown to be abundant in the Ord River irrigation area. The major mosquito breeding areas were in swampland adjacent to the diversion dam. Little breeding activity was found in the irrigation area probably due to the excessive use of insecticides applied by aerial spraying for controlling insect pests on cotton crops. However, cotton was discontinued as a crop in 1975, and an increased number of mosquitoes began to appear in 1976. • Viruses. Pools of mosquitoes were processed for virus isolation by intracerebral inoc-ulation of macerated mosquito supernatants into suckling mice. A total of 195 strains of 16 arboviruses were isolated from 1075 pools, of which 29 were identified as MVE virus and 21 as Kunjin virus. The majority of the isolates were made from Culex annulirostris (153 of 195 isolations), including 28 of 29 identified as MVE. Thus the overall virus isolation rate was high (18 per cent). For MVE virus from Culex annulirostris, 3.5 per cent of pools yielded virus at an approximate rate of 1 infected mosquito per 1459 uninfected mosquitoes (Liehne et al. 1976b; 1981). • Serological studies of animals and birds. All the early serological investigations employed the haemagglutination-inhibition (HI) assay. Cattle sera obtained from the Ord River irrigation area exhibited a high incidence of antibody to MVE virus (80 per cent positive), but the incidence declined to 37 per cent positivity in sera collected elsewhere in the Kimberley region (Liehne et al. 1976c). A very significant increase in the incidence of antibody to MVE was observed in cattle between 1972 and 1975 in the irrigation area and nearby cattle properties, with increases ranging from between 22 and 36 per cent to between 75 and 90 per cent (Stanley 1979). While the establishment of the irrigation area and the completion of the Ord River dam were undoubtedly responsible for some of this increase, it is probable that the very heavy ‘wet’ season rainfall in 1973–74 also contributed. • Of 335 sera collected from 31 avian species, 195 were found to have antibody to MVE virus. Although only a few species were sampled in moderate or large num-bers, it was interesting to note that the incidence of antibody was similar between waterbirds and non-waterbirds (56 and 59 per cent, respectively), and between differ-ent avian orders: Ciconiiformes (herons, egrets), 62 per cent; Anseriformes (ducks, grebes), 55 per cent; and Psittaciformes (parrots), 56 per cent, (Liehne et al. 1976c). • Human serological studies. A total of 441 human sera were collected in the Ord River area, of which 293 were from Caucasians and 148 from Aboriginals. A very high incidence of MVE antibodies was observed in the Aboriginal population, with 96 per cent of adults and 77 per cent of children exhibiting antibodies. In the Caucasian pop-ulation, the incidence of MVE virus antibodies was 53 per cent in adults and 24 per
DOI link for sion dam (Stanley 1979). Most of the species collected in the bait traps were those associated with permanent and semipermanent fresh water breeding sites, and the dominant species was Culex annulirostris, which accounted for over 70 per cent of the collections (Liehne et al. 1976a; Stanley 1979). Thus the major vector species for MVE virus was shown to be abundant in the Ord River irrigation area. The major mosquito breeding areas were in swampland adjacent to the diversion dam. Little breeding activity was found in the irrigation area probably due to the excessive use of insecticides applied by aerial spraying for controlling insect pests on cotton crops. However, cotton was discontinued as a crop in 1975, and an increased number of mosquitoes began to appear in 1976. • Viruses. Pools of mosquitoes were processed for virus isolation by intracerebral inoc-ulation of macerated mosquito supernatants into suckling mice. A total of 195 strains of 16 arboviruses were isolated from 1075 pools, of which 29 were identified as MVE virus and 21 as Kunjin virus. The majority of the isolates were made from Culex annulirostris (153 of 195 isolations), including 28 of 29 identified as MVE. Thus the overall virus isolation rate was high (18 per cent). For MVE virus from Culex annulirostris, 3.5 per cent of pools yielded virus at an approximate rate of 1 infected mosquito per 1459 uninfected mosquitoes (Liehne et al. 1976b; 1981). • Serological studies of animals and birds. All the early serological investigations employed the haemagglutination-inhibition (HI) assay. Cattle sera obtained from the Ord River irrigation area exhibited a high incidence of antibody to MVE virus (80 per cent positive), but the incidence declined to 37 per cent positivity in sera collected elsewhere in the Kimberley region (Liehne et al. 1976c). A very significant increase in the incidence of antibody to MVE was observed in cattle between 1972 and 1975 in the irrigation area and nearby cattle properties, with increases ranging from between 22 and 36 per cent to between 75 and 90 per cent (Stanley 1979). While the establishment of the irrigation area and the completion of the Ord River dam were undoubtedly responsible for some of this increase, it is probable that the very heavy ‘wet’ season rainfall in 1973–74 also contributed. • Of 335 sera collected from 31 avian species, 195 were found to have antibody to MVE virus. Although only a few species were sampled in moderate or large num-bers, it was interesting to note that the incidence of antibody was similar between waterbirds and non-waterbirds (56 and 59 per cent, respectively), and between differ-ent avian orders: Ciconiiformes (herons, egrets), 62 per cent; Anseriformes (ducks, grebes), 55 per cent; and Psittaciformes (parrots), 56 per cent, (Liehne et al. 1976c). • Human serological studies. A total of 441 human sera were collected in the Ord River area, of which 293 were from Caucasians and 148 from Aboriginals. A very high incidence of MVE antibodies was observed in the Aboriginal population, with 96 per cent of adults and 77 per cent of children exhibiting antibodies. In the Caucasian pop-ulation, the incidence of MVE virus antibodies was 53 per cent in adults and 24 per
sion dam (Stanley 1979). Most of the species collected in the bait traps were those associated with permanent and semipermanent fresh water breeding sites, and the dominant species was Culex annulirostris, which accounted for over 70 per cent of the collections (Liehne et al. 1976a; Stanley 1979). Thus the major vector species for MVE virus was shown to be abundant in the Ord River irrigation area. The major mosquito breeding areas were in swampland adjacent to the diversion dam. Little breeding activity was found in the irrigation area probably due to the excessive use of insecticides applied by aerial spraying for controlling insect pests on cotton crops. However, cotton was discontinued as a crop in 1975, and an increased number of mosquitoes began to appear in 1976. • Viruses. Pools of mosquitoes were processed for virus isolation by intracerebral inoc-ulation of macerated mosquito supernatants into suckling mice. A total of 195 strains of 16 arboviruses were isolated from 1075 pools, of which 29 were identified as MVE virus and 21 as Kunjin virus. The majority of the isolates were made from Culex annulirostris (153 of 195 isolations), including 28 of 29 identified as MVE. Thus the overall virus isolation rate was high (18 per cent). For MVE virus from Culex annulirostris, 3.5 per cent of pools yielded virus at an approximate rate of 1 infected mosquito per 1459 uninfected mosquitoes (Liehne et al. 1976b; 1981). • Serological studies of animals and birds. All the early serological investigations employed the haemagglutination-inhibition (HI) assay. Cattle sera obtained from the Ord River irrigation area exhibited a high incidence of antibody to MVE virus (80 per cent positive), but the incidence declined to 37 per cent positivity in sera collected elsewhere in the Kimberley region (Liehne et al. 1976c). A very significant increase in the incidence of antibody to MVE was observed in cattle between 1972 and 1975 in the irrigation area and nearby cattle properties, with increases ranging from between 22 and 36 per cent to between 75 and 90 per cent (Stanley 1979). While the establishment of the irrigation area and the completion of the Ord River dam were undoubtedly responsible for some of this increase, it is probable that the very heavy ‘wet’ season rainfall in 1973–74 also contributed. • Of 335 sera collected from 31 avian species, 195 were found to have antibody to MVE virus. Although only a few species were sampled in moderate or large num-bers, it was interesting to note that the incidence of antibody was similar between waterbirds and non-waterbirds (56 and 59 per cent, respectively), and between differ-ent avian orders: Ciconiiformes (herons, egrets), 62 per cent; Anseriformes (ducks, grebes), 55 per cent; and Psittaciformes (parrots), 56 per cent, (Liehne et al. 1976c). • Human serological studies. A total of 441 human sera were collected in the Ord River area, of which 293 were from Caucasians and 148 from Aboriginals. A very high incidence of MVE antibodies was observed in the Aboriginal population, with 96 per cent of adults and 77 per cent of children exhibiting antibodies. In the Caucasian pop-ulation, the incidence of MVE virus antibodies was 53 per cent in adults and 24 per
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