Powassan Virus: Persistence of Virus Activity During 1966

Powassan virus isolations were achieved from three of 60 pools of Ixodes cookei ticks removed from 286 groundhogs (Marmota monax) which were collected some 200 miles north of Toronto between May 5 and September 5, 1966. Virus yields per pool of one to 11 ticks ranged from 10^2.5 to 10^6.0 TCD₅₀ for primary swine kidney tissue cultures, and positive pools were collected on June 24, July 15 and August 10. Powassan neutralizing antibodies were detected by mouse inoculation tests in 143 of 362 animals including 127 of 286 groundhogs, 14 of 45 red squirrels (Tamiasciurus hudsonicus) and two of 31 other forest mammals. The monthly prevalence of antibody in the current season''s groundhogs increased from 0 to 25% with the progression of summer, but in older animals the incidence remained between 38 and 62% throughout the season. These results substantiate earlier findings which pointed towards the maintenance of Powassan virus in nature by a cycle involving groundhogs and squirrels as reservoirs, with ticks as vectors, from which human infections occurred tangentially.     

Powassan Virus: Vernal Spread During 1965

Powassan virus was isolated from seven pools of Ixodes cookei ticks removed from groundhogs (Marmota monax) collected near North Bay, Ontario, between May and August 1965, including five pools obtained during spring. Tick pools, each comprising one to nine ticks, contained 2.0 to 5.5 log₁₀ TCD₅₀ of virus upon titration in monolayer cultures of primary swine kidney cells. Powassan virus neutralizing antibody prevalence in sera of the current season''s groundhogs increased steadily from zero during May to 25% during August but remained relatively unchanged (42% to 58%) in the previous season''s groundhogs, thereby confirming that active infection had occurred particularly amongst juvenile groundhogs mainly during spring 1965. Isolation of one strain of Silverwater virus from Haemaphysalis leporis-palustris ticks and detection of neutralizing antibody in three of nine snowshoe hares (Lepus americanus) confirmed the active spread of this agent during 1965.     

Powassan Virus: Summer Infection Cycle, 1964

Between May 1, and September 15, 1964, neutralizing antibody to Powassan virus was detected in sera from 163 of 464 forest mammals captured in the Powassan—North Bay area of northern Ontario. These included 159 of 358 groundhogs and four of 43 red squirrels. Acquisition of antibody by juvenile groundhogs occurred principally during July and August. Powassan virus strains were isolated from tick pools containing two to 15 Ixodes cookei per pool which were removed from eight of 91 groundhogs in three townships during May, July and August. Virus was also recovered from blood of two groundhogs during May. Powassan virus was re-isolated from five of six tick pools and two blood clots by inoculation of swine kidney tissue cultures. These findings strongly suggest that during 1964 Powassan virus was maintained in nature by a cycle involving groundhogs and I. cookei ticks.     

一株保存的波瓦生病毒全基因组序列测定及分析

目的：对保存的WJBC株波瓦生病毒进行全基因组序列测定和分析,阐明其与已报道毒株之间的关系。方法：将波瓦生病毒基因组编码区分11段进行RT－PCR扩增,扩增产物直接进行测序,非编码区采用RACE法进行扩增,扩增产物纯化并连接pGEM－Teasy载体后转化大肠杆菌DH5ct感受态细胞,挑取阳性克隆鉴定后进行测序,用DNAstar软件将测序结果拼接得到全基因组序列。下载波瓦生病毒全基因组核苷酸序列,利用MEGA5．0软件构建系统进化发生树。结果与结论：WJBC株波瓦生病毒全基因组共11839nt,编码3415个氨基酸残基,病毒基因组5’端和3’端分别有111、483nt的非编码区;进化树结果显示,WJBC株波瓦生病毒与LB株波瓦生病毒的亲缘性最高,可能为同一病毒株．．     

Brevipalpus-Transmitted Plant Virus and Virus-Like Diseases: Cytopathology and Some Recent Cases

An increasing number of diseases transmitted by Brevipalpus mite species (Acari: Tenuipalpidae) is being identified that affect economically important plants such as citrus, coffee, passion fruit, orchids, and several ornamentals. All of these diseases are characterized by localized lesions (chlorotic, green spots, or ringspots) on leaves, stems, and fruits. Virus or virus-like agents are considered to be the causal agents, possibly transmitted in a circulative-propagative manner by Brevipalpus mites. The virus or virus-like particles are short, rod-like, or bacilliform, that induce two characteristic types of cell alteration: (1) 'Nuclear type'--nuclei of parenchyma and epidermal cells in the lesions often contain a large electron lucent inclusion. Short, naked, rod-like (40-50 nm x 100-110 nm) particles may be seen in the viroplasm or nucleoplasm and in the cytoplasm. These particles are commonly arranged perpendicularly on the membranes of the nuclear envelope or endoplasmic reticulum (ER). In a very few instances, they were found to be membrane-bound, within the ER cavities. (2) 'Cytoplasmic type'--short bacilliform particles (60-70 nm x 110-120 nm) are present within the cisternae of the ER and often have electron dense viroplasm of varied shapes present in the cytoplasm. Bacilliform particles may be seen budding into the ER lumen near the viroplasm. These particles resemble those of members of the Rhabdoviridae, but are shorter. The only sequenced virus of this group, orchid fleck virus (OFV), has a negative sense (bipartite) type ssRNA genome, but its organization is similar to known rhabdoviruses, which are monopartite. Both types of cytopathological effects have been found associated with citrus leprosis. In orchids, OFV has a 'nuclear type' of cytopathology, but in some species the 'cytoplasmic type' has been found associated with ringspot symptoms. In Hibiscus and Clerodendron, green spot symptoms have been associated with the cytoplasmic type of cell alteration, while chlorotic spots, in the same species, are associated with the nuclear type. In a few cases, both types of cytopathological effects have been found in the same tissue and cell.     

Cytopathology of Anthers and Pollen From Lettuce Plants Infected by Lettuce Mosaic Virus

Thin sections of mature anthers and pollen grains from three lettuce (Lactuca sativa) plants infected with lettuce mosaic potyvirus (LMV) were studied by immunogold labelling. Labelled LMV particles were present externally on the exine of pollen grains from all plants, but were observed internally in the pollen grains from only one plant. Within mature pollen grains the virus particles were associated with the cytoplasmic bundle inclusions typical of infection by potyviruses. The tapetal plasmodium and the epidermal and endothecial layers of mature anthers from all infected plants also contained labelled virus particles, together with pinwheel and bundle inclusions.     

鳜鱼病毒结构特征与形态发生

从患流行病的鳜鱼脾脏组织超微切片中观察到大量的病毒颗粒.该完整病毒颗粒直径约135nm±10,具包膜.成熟病毒核壳体约90nm±5,包膜厚度约18nm±3,核壳体与包膜间的非电子致密区约有27nm±2.通过对不同发病阶段发病鳜鱼脾脏组织切片的电镜观察,在感染初期的鳜鱼脾脏组织观察到病毒的吸附及典型的内吞入侵方式,在感染中后期的脾脏组织细胞质内观察到病毒发生基质及病毒核壳、包膜形成与病毒的释放.此外,在染病鳜鱼的肾、心、肝、及鳃组织亦观察到相同结构的病毒粒子.回接实验证实该病毒为引起鳜鱼暴发流行病的病原.     

鳜鱼病毒结构特征与形态发生

从患流行病的鳜鱼脾脏组织超微切片中观察到大量的病毒颗粒。该完整病毒颗粒直径约 135nm± 10 ,具包膜。成熟病毒核壳体约 90nm± 5 ,包膜厚度约 18nm± 3,核壳体与包膜间的非电子致密区约有 2 7nm± 2。通过对不同发病阶段发病鳜鱼脾脏组织切片的电镜观察 ,在感染初期的鳜鱼脾脏组织观察到病毒的吸附及典型的内吞入侵方式 ,在感染中后期的脾脏组织细胞质内观察到病毒发生基质及病毒核壳、包膜形成与病毒的释放。此外 ,在染病鳜鱼的肾、心、肝、及鳃组织亦观察到相同结构的病毒粒子。回接实验证实该病毒为引起鳜鱼暴发流行病的病原     

Powassan and Silverwater Viruses: Ecology of Two Ontario Arboviruses

Powassan virus was isolated from a pool of Ixodes marxi ticks collected during late August 1962, from a red squirrel, Tamiasciurus hudsonicus, and from blood obtained from a red squirrel during early October 1962 near Powassan, Ontario, where a child contracted fatal encephalitis due to this virus in September 1958. The frequent detection of Powassan virus neutralizing antibody in sera of squirrels captured during autumn, but rarely at other seasons, and the frequent I. marxi infestation of squirrels, some of which contain antibody, but the lack of occurrence of I. marxi on other forest rodents, suggest that I. marxi ticks are vectors and squirrels are reservoirs of Powassan virus infection. Isolation of Silverwater virus from Haemaphysalis leporis-palustris ticks which infested a snowshoe hare Lepus americanus near Powassan demonstrates the presence of this agent in the Powassan area also.     

Morphology and Development of Bovine Ephemeral Fever Virus

The development of the virus of bovine ephemeral fever in mouse brain has been studied by electron microscopy. The virus particles are bullet-shaped, 70 by 145 nm, and slightly tapered toward the rounded end. The outer envelope is closely apposed to an electron-dense shell, about 12 nm thick, but no other internal structure is visible. The virus strains studied bud from the marginal membranes of neurones, but intracytoplasmic development, possibly aberrant, was also observed with one strain. Ephemeral fever virus is thus obviously a rhabdovirus, with points of resemblance to vesicular stomatitis, Flanders-Hart Park, and Kern Canyon viruses on the one hand, and to rabies virus on the other, but is structurally distinct from any of these.     

In Vitro Morphology and Maturation of Lymphocystis Virus

The temporal sequence of development of lymphocystis disease virus (LDV) was studied by electron microscopy of thin sections of infected tissue-culture monolayers. Neither the typical cytoplasmic inclusion nor virus was detected at 4 days postinfection (PI). Inclusions, but no viruses, were detected at 8 days PI. Inclusions and associated virions were detected at 15 days PI, and by 28 days PI the undisrupted cells were filled with the typical virions. No release mechanism was detected, and severe clumping of particles was noted. Negatively stained preparations revealed particles 200 nm in diameter with no capsomere structure and apparent spikes associated with the particle. The relationship of LDV to the well-defined deoxyribonucleic acid virus groups is discussed.