Aspectos biológicos do ácaro Brevipalpus phoenicis vetor da leprose dos citros em plantas de buva (Conyza canadensis)

O ácaro Brevipalpus phoenicis, vetor da leprose dos citros, é uma espécie polífaga que tem ampla gama de hospedeiros alternativos nos pomares cítricos, nos quais se pode manter e/ou incrementar suas populações. O objetivo deste trabalho foi estudar a sobrevivência, a oviposição e o modo de alimentação do ácaro B. phoenicis em plantas de buva (Conyza canadensis) com diferentes tamanhos. Para avaliação da sobrevivência e oviposição do ácaro B. phoenicis, foi utilizado o delineamento estatístico inteiramente casualizado, com cinco tratamentos e doze repetições. Os tratamentos estudados foram: (1) secções de caules de plantas menores que 20 cm, (2) entre 21 e 50 cm, (3) entre 51 e 100 cm e (4) maiores que 101 cm de altura; e (5) secções de ramos de laranja. Dez fêmeas adultas de B. phoenicis, procedentes de uma criação-estoque, foram transferidas para cada secção de caule de buva e ramos de citros como testemunha. Avaliou-se a sobrevivência e a oviposição dos ácaros até 120 horas após a transferência. Alguns aspectos comportamentais do ácaro B. phoenicis foram fotomicrografados, utilizando-se microscópico eletrônico de varredura. Verificou-se que as plantas de maior altura de buva foram mais favoráveis à sobrevivência do ácaro B. phoenicis do que as de menor tamanho. Contudo, a quantidade de ovos postos pelo ácaro não diferiu em relação à altura das plantas de buva. Com base nas fotomicrografias, constatou-se a preferência do ácaro B. phoenicis por se alimentar na base dos tricomas presentes na superfície do caule da planta de buva, justificado, possivelmente, pela maior turgescência das células encontradas nessa região da planta. Esses resultados reforçam a importância do manejo de buva nos pomares cítricos, pois a sua presença no campo pode favorecer a sobrevivência e o desenvolvimento do ácaro B. phoenicis, servindo, portanto, como hospedeira alternativa, o que pode contribuir para a disseminação do ácaro e, consequentemente, da leprose nos pomares cítricos.

In vitro expression and antiserum production against the movement protein of Citrus leprosis virus C (CiLV-C)

Citrus leprosis, caused by Citrus leprosis virus C (CiLV-C), is currently considered the most important viral disease in the Brazilian citrus industry due to the high costs required for the chemical control of its vector, the mite Brevipalpus phoenicis. The pathogen induces a non-systemic infection and the disease is characterized by the appearance of localized lesions on citrus leaves, stems and fruits, premature fruit and leaf drop and dieback of stems. Attempts were made to promote in vitro expression of the putative cell-to-cell movement protein of CiLV-C in Escherichia coli and to produce a specific polyclonal antibody against this protein as a tool to investigate the virus-plant-vector relationship. The antibody reacted strongly with the homologous protein expressed in vitro by ELISA, but poorly with the native protein present in leaf lesion extracts from sweet orange caused by CiLV-C. Reactions from old lesions were more intense than those from young lesions. Western blot and in situ immunolocalization assays failed to detect the native protein. These results suggest low expression of the movement protein (MP) in host tissues. Moreover, it is possible that the conformation of the protein expressed in vitro and used to produce the antibody differs from that of the native MP, hindering a full recognition of the latter.

In vitro expression and antiserum production against the movement protein of Citrus leprosis virus C (CiLV-C)

Citrus leprosis, caused by Citrus leprosis virus C (CiLV-C), is currently considered the most important viral disease in the Brazilian citrus industry due to the high costs required for the chemical control of its vector, the mite Brevipalpus phoenicis. The pathogen induces a non-systemic infection and the disease is characterized by the appearance of localized lesions on citrus leaves, stems and fruits, premature fruit and leaf drop and dieback of stems. Attempts were made to promote in vitro expression of the putative cell-to-cell movement protein of CiLV-C in Escherichia coli and to produce a specific polyclonal antibody against this protein as a tool to investigate the virus-plant-vector relationship. The antibody reacted strongly with the homologous protein expressed in vitro by ELISA, but poorly with the native protein present in leaf lesion extracts from sweet orange caused by CiLV-C. Reactions from old lesions were more intense than those from young lesions. Western blot and in situ immunolocalization assays failed to detect the native protein. These results suggest low expression of the movement protein (MP) in host tissues. Moreover, it is possible that the conformation of the protein expressed in vitro and used to produce the antibody differs from that of the native MP, hindering a full recognition of the latter.

Transmission of Citrus leprosis virus C by Brevipalpus phoenicis (Geijskes) to Alternative Host Plants Found in Citrus Orchards

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Complete nucleotide sequence, genomic organization and phylogenetic analysis of Citrus leprosis virus cytoplasmic type

The complete nucleotide sequence of the genomic RNA 1 (8745 nt) and RNA 2 (4986 nt) of Citrus leprosis virus cytoplasmic type (CiLV-C) was determined using cloned cDNA. RNA 1 contains two open reading frames (ORFs), which correspond to 286 and 29 kDa proteins. The 286 kDa protein is a polyprotein putatively involved in virus replication, which contains four conserved domains: methyltransferase, protease, helicase and polymerase. RNA 2 contains four ORFs corresponding to 15, 61, 32 and 24 kDa proteins, respectively. The 32 kDa protein is apparently involved in cell-to-cell movement of the virus, but none of the other putative proteins exhibit any conserved domain. The 5' regions of the two genomic RNAs contain a 'cap' structure and poly(A) tails were identified in the 3'-terminals. Sequence analyses and searches for structural and non-structural protein similarities revealed conserved domains with members of the genera Furovirus, Bromovirus, Tobravirus and Tobamovirus, although phylogenetic analyses strongly suggest that CiLV-C is a member of a distinct, novel virus genus and family, and definitely demonstrate that it does not belong to the family Rhabdoviridae, as previously proposed. Based on these results it was proposed that Citrus leprosis virus be considered as the type member of a new genus of viruses, Cilevirus.

Weather variability, tides, and Barmah Forest Virus Disease in the Gladstone region, Australia

In this study we examined the impact of weather variability and tides on the transmission of Barmah Forest virus (BFV) disease and developed a weather-based forecasting model for BFV disease in the Gladstone region, Australia. We used seasonal autoregressive integrated moving-average (SARIMA) models to determine the contribution of weather variables to BFV transmission after the time-series data of response and explanatory variables were made stationary through seasonal differencing. We obtained data on the monthly counts of BFV cases, weather variables (e.g., mean minimum and maximum temperature, total rainfall, and mean relative humidity), high and low tides, and the population size in the Gladstone region between January 1992 and December 2001 from the Queensland Department of Health, Australian Bureau of Meteorology, Queensland Department of Transport, and Australian Bureau of Statistics, respectively. The SARIMA model shows that the 5-month moving average of minimum temperature (β = 0.15, p-value < 0.001) was statistically significantly and positively associated with BFV disease, whereas high tide in the current month (β = −1.03, p-value = 0.04) was statistically significantly and inversely associated with it. However, no significant association was found for other variables. These results may be applied to forecast the occurrence of BFV disease and to use public health resources in BFV control and prevention.

Geographic Variation of Notified Ross River Virus Infections in Queensland, Australia, 1985-1996

The spatial and temporal variations of Ross River virus infections reported in Queensland, Australia, between 1985 and 1996 were studied by using the Geographic Information System. The notified cases of Ross River virus infection came from 489 localities between 1985 and 1988, 805 between 1989 and 1992, and 1,157 between 1993 and 1996 (chi2(df = 2) = 680.9; P < 0.001). There was a marked increase in the number of localities where the cases were reported by 65 percent for the period of 1989-1992 and 137 percent for 1993-1996, compared with that for 1985-1988. The geographic distribution of the notified Ross River virus cases has expanded in Queensland over recent years. As Ross River virus disease has impacted considerably on tourism and industry, as well as on residents of affected areas, more research is required to explore the causes of the geographic expansion of the notified Ross River virus infections.

Experimental Infection of Culex Annulirostris, Culex Gelidus, and Aedes Vigilax With a Yellow Fever/Japanese Encephalitis Virus Vaccine Chimera (Chimerivax TM-JE)

Australian mosquitoes from which Japanese encephalitis virus (JEV) has been recovered (Culex annulirostris, Culex gelidus, and Aedes vigilax) were assessed for their ability to be infected with the ChimeriVax-JE vaccine, with yellow fever vaccine virus 17D (YF 17D) from which the backbone of ChimeriVax-JE vaccine is derived and with JEV-Nakayama. None of the mosquitoes became infected after being fed orally with 6.1 log(10) plaque-forming units (PFU)/mL of ChimeriVax-JE vaccine, which is greater than the peak viremia in vaccinees (mean peak viremia = 4.8 PFU/mL, range = 0-30 PFU/mL of 0.9 days mean duration, range = 0-11 days). Some members of all three species of mosquito became infected when fed on JEV-Nakayama, but only Ae. vigilax was infected when fed on YF 17D. The results suggest that none of these three species of mosquito are likely to set up secondary cycles of transmission of ChimeriVax-JE in Australia after feeding on a viremic vaccinee.