Differential diagnosis of two paralytic conditions affecting young chickens with emphasis on PCR findings.

Two paralytic conditions affecting flocks of young commercial chickens that were indistinguishable histopathologically from lesions caused by Marek's disease virus (MDV) were investigated. The first, transient paralysis, was observed only in broilers while the second condition, a spastic paralysis, was seen in replacement White Leghorn pullets aged between 6 and 16 weeks. PCR examination of DNA extracted from the blood, brain and spleens of affected birds using primers specific for MDV serotype 1 confirmed the diagnosis of MD for transient paralysis only.

Replication of non-defective reticuloendotheliosis viruses in the avian embryo assayed by PCR and immunofluorescence.

Congenital transmission of reticuloendotheliosis virus (REV) is known to occur when one of the parents in either tolerantly infected or viraemic; however little attention has been paid to replication of the virus within the embryo itself. In this study five non-defective and one replication-defective strain of REV were inoculated into the yolk sac of 6-day-old embryonated eggs. With the exception of one non-defective strain, the others induced embryonic deformation or lesions that were apparent on the day of hatching.

Safety and efficacy in geese of a PER.C6-based inactivated West Nile virus vaccine.

Studies were performed with an inactivated vaccine against the mosquito-borne flavivirus, West Nile virus (WNV). The mammalian cell line, PER.C6, was selected as the platform for WNV growth since both the neurovirulent strains NY99 and ISR98 that cause epidemics in humans and high mortality in geese, respectively, could be propagated to high titers (10(9) to 10(10)TCID(50)/ml) on these cells.

Experimental infection of common garter snakes (Thamnophis sirtalis) with West Nile virus.

The role of various reptilian species in the infectious cycle of several arboviruses is documented, but their role in that of West Nile virus (WNV) is uncertain. Common garter snakes (Thamnophis sirtalis) were infected subcutaneously with 10(5) plaque forming units (PFU) WNV-Isr 98, five of nine snakes became viremic, and five exhibited persistent low levels of neutralizing antibodies. Four of the parentally infected snakes died and high titers of virus were found in multiple organ samples.

An inactivated West Nile virus vaccine for domestic geese-efficacy study and a summary of 4 years of field application.

Following the isolation in 1997 of West Nile virus from the brains of geese with an acute neuroparalytic disease in Israel, which reappeared in the following years, an inactivated vaccine was prepared from suckling mouse brains. The brain homogenate was inactivated with formaldehyde and blended with mineral oil adjuvant. In 2000, the first flocks were vaccinated according to a schedule of two subcutaneous doses, commencing at the age of 2 weeks and given with a 2-weeks interval.

Adeno-associated virus type 2 enhances goose parvovirus replication in embryonated goose eggs.

The autonomous goose parvovirus (GPV) and the human helper-dependent adeno-associated virus type 2 (AAV2) share a high degree of homology. To determine if this evolutionary relationship has a biological impact, we studied viral replication in human 293 cells and in embryonated goose eggs coinfected with both viruses. Similar experiments were performed with the minute virus of mice (MVM), an autonomous murine parvovirus with less homology to AAV2.

Argasid ticks as possible vectors of West Nile virus in Israel.

Mites and soft ticks collected directly from wild and domestic birds and their nests were tested for the presence of West Nile virus (WNV). The cattle egret argas, Argas arboreus, was collected from the nests of seven cattle egret colonies. Out of 1,000 A.

Application of diagnostic procedures to epidemiological situations with special reference to arboviral infections.

The rationale behind the methodology employed to investigate a new disease that appears in an area hitherto unaffected is fundamentally different from that applied in an endemic disease situation. Special consideration must also be given to disease agents that appear and reappear at cyclical intervals. The authors present three separate approaches applicable in three different epidemiological situations.

Comparison of serological and virological findings from subgroup J avian leukosis virus-infected neoplastic and non-neoplastic flocks in Israel.

Blood samples from nine broiler breeder flocks comprising five flocks clinically affected with myeloid leukosis tumours (ML+) and four tumour-free flocks from the same commercial background (ML-) were compared for avian leukosis virus subgroup J (ALV-J) serum antibodies by enzyme-linked immunosorbent assay (ELISA), for antigenemia (group-specific antigen) by antigen-trapping ELISA and for viremia. Group-specific antigen was detected in the sera of 58.1% of ML+ birds and 46.

A twelve-month study of West Nile virus antibodies in a resident and a migrant species of kestrels in Israel.

Two species of kestrel, the common and lesser, were caught each month at three geographically defined locations in Israel over a 12-month period, and a total of 306 blood samples were examined for West Nile virus neutralizing antibodies. The prevalences and mean antibody titers were analyzed statistically by the multiple linear regression model and were shown to be significantly affected by two of the independent variables, location and age of the bird. The season had no overall effect on prevalence and titer but a comparison of the mean monthly titers revealed that April was highest and July and August the lowest statistically for the common kestrel which is a resident species.

Direct (non-vector) transmission of West Nile virus in geese.

During a recent epizootic, losses due to West Nile virus (WNV) infection in young goose flocks were estimated to be far greater than expected if mosquito-borne transmission was the principal route of infection. Contact transmission was investigated experimentally as an alternative explanation. A group of 10, 3-week-old geese were inoculated subcutaneously and placed in one insect-proof room with 20 geese of the same age.

Phylogenetic relationships of West Nile viruses isolated from birds and horses in Israel from 1997 to 2001.

In November 1997, an outbreak of a neuroparalytic disease caused by West Nile (WN) virus was diagnosed in young goose flocks. Domestic geese were similarly affected in the late summer and fall of 1998, 1999, 2000 and 2001. WN viruses were also isolated from migratory and wild birds and horses in 1998-2001.

The role of birds in the ecology of West Nile virus in Europe and Africa.

Surveys on wild birds conducted during the last two decades in Europe, notably Poland and the Czech Republic, to determine their infection rate with WN virus have revealed endemic foci of infection. Some species of seropositive birds were nonmigrators while others were hatchlings of migrating species. Persistently infected avian reservoirs are potential sources of viruses for mosquitoes that multiply in the temperate European zone in hot, wet summers.

Marek's disease in turkeys. II. Characterization of the viral glycoprotein B gene and antigen of a turkey strain of Marek's disease virus.

Marek's disease virus (MDV) causes immunosuppression and tumors in chickens. As sporadic cases of Marek's disease (MD) were recorded in turkeys, the antigenic and genomic characteristics of the MDV glycoprotein B (gB) gene and antigen of turkeys were compared to the chicken MDV gB. The whole chicken and turkey gB genes were sequenced and found identical.

Marek's disease in turkeys. I. A seven-year survey of commercial flocks and experimental infection using two field isolates.

Marek's disease virus (MDV) causes immunosuppression and tumors in chickens, but the turkey is an unusual host for the virus, and tumors caused by MDV in turkeys are unique. We describe the prevalence of turkey tumors in Israel between 1993 and 2000, their molecular diagnosis by polymerase chain reaction (PCR), and the natural distribution of herpesvirus of turkeys (HVT). Most clinical cases with tumors in commercial turkeys were diagnosed as MDV.

Introduction of West Nile virus in the Middle East by migrating white storks.

West Nile virus (WNV) was isolated in a flock of 1,200 migrating white storks that landed in Eilat, a town in southern Israel, on August 26, 1998. Strong, hot westerly winds had forced the storks to fly under considerable physical stress before reaching the agricultural land surrounding the town. Most of the flock were fledglings, <1 year old, which had hatched in Europe.

Use of live and inactivated vaccines in the control of West Nile fever in domestic geese.

The recent epizootic of West Nile fever in Israel affected predominantly young domestic geese between three and eight weeks old. Clinically, the birds presented paralytic signs while morbidity and mortality were severe in affected flocks. The condition was encountered from early September through late November on goose farms located throughout the country.

Variations in biological features of West Nile viruses.

Pathological findings in humans, horses, and birds with West Nile (WN) encephalitis show neuronal degeneration and necrosis in the central nervous system (CNS), with diffuse inflammation. The mechanisms of WN viral penetration of the CNS and pathophysiology of the encephalitis remain largely unknown. Since 1996, several epizootics involving hundreds of humans, horses, and thousands of wild and domestic bird cases of encephalitis and mortality have been reported in Europe, North Africa, the Middle East, Russia, and the USA (see specific chapters in this issue).

West Nile fever in Israel 1999-2000: from geese to humans.

West Nile virus (WNV) caused disease outbreaks in Israel in the 1950s and the late 1970s. In 1998 an outbreak of WNV in goose farms and evidence of infection in dead migratory birds were reported. Consequently, human diagnostic services for WNV were resumed, including virus isolation, serology, and RT-PCR.

A live attenuated West Nile virus strain as a potential veterinary vaccine.

This article reviews the development of two attenuated West Nile virus (WNV) variants, WNI-25 and WNI-25A. These variants have lost the neuroinvasion trait of the parental virus. Attenuation was achieved through serial passages in mosquito cells and neutralization escape from WNV-specific monoclonal antibody.

Diagnosis of turkey meningoencephalitis virus infection in field cases by RT-PCR compared to virus isolation in embryonated eggs and suckling mice.

Turkey meningoencephalitis (TME) is a paralytic epornitic disease of turkeys caused by turkey meningoencephalitis virus (TMEV), an arthopod-borne flavivirus belonging to the Ntaya serogroup VI. A TMEV specific RT-PCR was compared with classical techniques for TMEV diagnosis, which include virus isolation in 8-day-old chicken embryonated eggs and suckling mice, on 17 TME flocks with neurological signs that occurred during the fall of 1997. In 11/17 flocks both the RT-PCR and the virus isolation methods detected virus, in 4/17 flocks a negative diagnosis was obtained by both methods, and two flocks were positive by RT-PCR only.

Origin of the West Nile virus responsible for an outbreak of encephalitis in the northeastern United States.

In late summer 1999, an outbreak of human encephalitis occurred in the northeastern United States that was concurrent with extensive mortality in crows (Corvus species) as well as the deaths of several exotic birds at a zoological park in the same area. Complete genome sequencing of a flavivirus isolated from the brain of a dead Chilean flamingo (Phoenicopterus chilensis), together with partial sequence analysis of envelope glycoprotein (E-glycoprotein) genes amplified from several other species including mosquitoes and two fatal human cases, revealed that West Nile (WN) virus circulated in natural transmission cycles and was responsible for the human disease. Antigenic mapping with E-glycoprotein-specific monoclonal antibodies and E-glycoprotein phylogenetic analysis confirmed these viruses as WN.