Transmission and Pathogenicity of Papaya Virus E: Insights from an Experimental Papaya Orchard.

A study was conducted to investigate epidemiological aspects of papaya virus E (PpVE), a cytorhabdovirus commonly found in papaya (Carica papaya L.) plantings in Ecuador. Besides papaya, PpVE was found in three Fabaceae weeds, including Rhynchosia minima, Centrosema plumieri, and Macroptilium lathyroides, the latter being the species with the highest virus prevalence. Greenhouse experiments showed that in M. lathyroides, single infections of PpVE induce only mild leaf mosaic, whereas in mixed infections with cowpea severe mosaic virus, PpVE contributes to severe mosaic. In papaya, PpVE did not induce noticeable symptoms in single or mixed infections with papaya ringspot virus. Transmission experiments confirmed that whiteflies (Bemisia tabaci) transmit PpVE in a semipersistent, nonpropagative manner.

Genetic characterization of a mild isolate of papaya ringspot virus type-P (PRSV-P) and assessment of its cross-protection potential under greenhouse and field conditions.

A mild isolate of Papaya ringspot virus type-P, abbreviated as PRSV-mild, from Ecuador was sequenced and characterized. The most distinguishing symptom induced by PRSV-mild was gray powder-like leaf patches radiating from secondary veins. In greenhouse experiments, PRSV-mild did not confer durable protection against a severe isolate of the virus (PRSV-sev), obtained from the same field. Furthermore, isolate specific detection in mixed-infected plants showed that PRSV-sev becomes dominant in infections, rendering PRSV-mild undetectable at 90-120 days post superinfection. Virus testing using isolate-specific primers detected PRSV-mild in two out of five surveyed provinces, with 10% and 48% of incidence in Santo Domingo and Los Ríos, respectively. Comparative genomics showed that PRSV-mild lacks two amino acids from the coat protein region, whereas amino acid determinants for asymptomatic phenotypes were not identified. Recombination events were not predicted in the genomes of the Ecuadorean isolates. Phylogenetic analyses placed both PRSV-mild and PRSV-sev in a clade that includes an additional PRSV isolate from Ecuador and others from South America.

Sequencing, genome analysis and prevalence of a cytorhabdovirus discovered in Carica papaya.

The complete genome of a new rhabdovirus infecting papaya (Carica papaya L.) in Ecuador, named papaya virus E, was sequenced and characterized. The negative-sense single-stranded RNA genome consists of 13,469 nucleotides with six canonical open reading frames (ORFs) and two accessory short ORFs predicted between ORFs corresponding to P3 (movement protein) and M (matrix protein). Phylogenetic analyses using amino acid sequences from the nucleocapsid, glycoprotein and polymerase, grouped the virus with members of the genus Cytorhabdovirus, with rice stripe mosaic virus, yerba mate chlorosis-associated virus and Colocasia bobone disease-associated virus as closest relatives. The 3' leader and 5' trailer sequences were 144 and 167 nt long, respectively, containing partially complementary motifs. The motif 3'-AUUCUUUUUG-5', conserved across rhabdoviruses, was identified in all but one intergenic regions; whereas the motif 3'-ACAAAAACACA-5' was found in three intergenic junctions. This is the first complete genome sequence of a cytorhabdovirus infecting papaya. The virus was prevalent in commercial plantings of Los Ríos, the most important papaya producing province of Ecuador. Recently, the genome sequence of bean-associated cytorhabdovirus was reported. The genome is 97% identical to that of papaya virus E, indicating that both should be considered strains of the same virus.

Sarcocystis cymruensis: discovery in Western Hemisphere in the Brown rat (Rattus norvegicus) from Grenada, West Indies: redescription, molecular characterization, and transmission to IFN-γ gene knockout mice via sporocysts from experimentally infected domestic cat (Felis catus).

Rodents are intermediate hosts for many species of Sarcocystis. Little is known of Sarcocystis cymruensis that uses the Brown rat (Rattus norvegicus) as intermediate hosts and the domestic cat (Felis catus) as experimental definitive host. Here, we identified and described Sarcocystis cymruensis in naturally infected R. norvegicus from Grenada, West Indies. Rats (n = 167) were trapped in various locations in two parishes (St. George and St. David). Microscopic, thin (< 1 µm) walled, slender sarcocysts were found in 11 of 156 (7.0%) rats skeletal muscles by squash examination. A laboratory-raised cat fed naturally infected rat tissues excreted sporocysts that were infectious for interferon gamma gene knockout (KO) mice, but not to Swiss Webster outbred albino mice. All inoculated mice remained asymptomatic, and microscopic S. cymruensis-like sarcocysts were found in the muscles of KO mice euthanized on day 70, 116, and 189 post inoculation (p.i.). Sarcocysts from infected KO mice were infective for cats at day 116 but not at 70 days p.i. By transmission electron microscopy, the sarcocyst wall was "type 1a." Detailed morphological description of the cyst wall, metrocytes, and bradyzoites is given for the first time. Additionally, molecular data on S. cymruensis are presented also for the first time. Molecular characterization of sarcocysts 18S rDNA and 28S rDNA, ITS-1, and cox1 loci showed the highest similarity with S. rodentifelis and S. muris. In conclusion, the present study described the natural infection of S. cymruensis in Brown rat for the first time in a Caribbean country and provided its molecular characteristics.