Impact of contact investigation and tuberculosis screening among high-risk groups in Denmark.

SETTING: The objective of tuberculosis (TB) screening in low-incidence countries is to identify TB patients earlier, ideally to improve health outcomes and reduce Mycobacterium tuberculosis transmission. In this retrospective study, we compare hospitalisation (morbidity) and smear positivity rates (infectiousness) in TB patients identified through active case finding (ACF) with patients identified through passive case finding (PCF). METHODS: ACF patients were identified by screening socially marginalised persons or through contact investigation. Logistic regression was used to model the associations between case-finding group (ACF/PCF) and hospitalisation, and between case-finding group and smear positivity rates. RESULTS: A total of 108 patients were identified through ACF and 332 through PCF. Thirty (27.8%) ACF patients and 153 (46.1%) PCF patients were hospitalised. In the adjusted models, ACF patients (OR 0.24, P 0.001) and ACF subgroups identified using mobile X-ray screening, spot sputum culture screening and contact investigation were significantly less likely to be hospitalised than PCF patients. Thirty-one (34.4%) ACF patients and 127 (50.4%) PCF patients were smear-positive. ACF patients (OR 0.30, P 0.001) and ACF subgroups identified through contact investigation and spot sputum culture screening were less likely to be smear-positive than PCF patients. CONCLUSIONS: These findings suggest that ACF reduces morbidity and infectiousness among TB patients, thereby potentially improving health outcomes and reducing transmission of M. tuberculosis.

Seed Transmission of the High Plains virus in Sweet Corn.

The High Plains virus (HPV), which infects corn and other cereals, was first found in 1993 in the United States. Research was initiated in 1995 to investigate the potential for seed transmission of HPV. Sweet corn seeds of various cultivars harvested in 1994 to 1996 from 13 fields and research plots in southwestern Idaho, Colorado, and Nebraska were seeded in potting mix in the greenhouse. Leaf samples collected at the three- to six-leaf stage from both symptomatic and asymptomatic plants were tested by enzyme-linked immunosorbent assay (ELISA). Of the 46,600 seeds planted, 38,473 seedlings emerged, and three tested positive by ELISA, exhibited mosaic symptoms, and had the presence of HPV confirmed by an additional test. One of the positive plants was used for successful acquisition and transmission of HPV by the wheat curl mite to Westford barley. The other two plants were used to successfully transfer HPV to other corn plants by vascular puncture inoculation of seed. These results indicate that HPV can be seed transmitted at a very low frequency in sweet corn.

High plains disease of corn and wheat: ultrastructural and serological aspects.

Virus-like particles with unique size and morphology were consistently associated with a new eriophyid mite-borne disease of maize and wheat, the high plains disease. In cells of symptomatic leaves, double membrane-bound particles (DMPs), quasi-spherical structures 120-200 nm in diameter, were present throughout the cytoplasm in association with electron-dense amorphous inclusions. No DMPs and inclusions were observed in symptomless plants. The DMPs were morphologically indistinguishable from those associated with eriophyid mite-borne diseases of uncertain etiology: fig mosaic, rose rosette, yellow ringspot of redbud, thistle mosaic, wheat spot chlorosis and wheat spot mosaic diseases. The DMPs and associated viroplasm-like inclusions in maize and wheat were specifically immunogold labeled in situ with an antiserum to the 32 kDa protein associated specifically with the high plains disease. Thread-like structures, present in the purified preparations from diseased maize were also immunogold labeled with the antiserum. It is suggested that the thread-like structures are derived from the DMPs. In many cells of symptomatic maize and wheat samples, DMPs occurred together with flexuous rod-shaped particles and cylindrical inclusions of wheat streak mosaic potyvirus (WSMV), indicating that these cells are infected doubly with WSMV and the agent represented by the DMPs.

Mixed Infection of Hard Red Winter Wheat with High Plains Virus and Wheat Streak Mosaic Virus from Wheat Curl Mites in Nebraska.

A new disease of wheat and corn caused by the High Plains virus (HPV) has been observed in the High Plains region of western United States. HPV is transmitted by the wheat curl mite, Aceria tosichella, which is also the vector of wheat streak mosaic virus (WSMV). In the field it is extremely difficult to visually differentiate plants infected with WSMV from those with HPV. An indirect protein-A sandwich enzyme-linked immunosorbent assay (PAS-ELISA) and Western blot analysis were used to identify WSMV and HPV. Samples of wheat curl mites were collected from arbitrarily chosen sites from commercial wheat plantings in 1995 and 1996 and used to infest caged wheat plants. After 3 weeks, leaf samples were harvested and assayed. Both Western blot analysis and PAS-ELISA were effective at identifying samples positive for WSMV and HPV, both alone and in mixed infections. Western blot results showed that over the 2 years, 65% of the samples were positive for WSMV, 46% were positive for HPV, and mixed infections were found in 40% of the samples. HPV presence was verified with similar results from field collected plant samples. These levels of virus indicate an unexpectedly high incidence of HPV in wheat curl mite populations in Nebraska.

Molecular cloning, sequencing, and phylogenetic relationships of a new potyvirus: sugarcane streak mosaic virus, and a reevaluation of the classification of the potyviridae.

The nucleic acid of a serologically distinct potyvirus, originally isolated out of sugar cane from Pakistan, was reverse transcribed and the 3' terminal 2000 bp was PCR amplified, cloned, and sequenced. Phylogenetic comparisons of viruses representing each genus of the Potyviridae show that the Pakistani isolate is most closely related to the rymoviruses wheat streak mosaic virus (WSMV) and brome streak mosaic virus. We therefore propose that this new virus species be named sugar cane streak mosaic virus to reflect its similarity to WSMV. The phylogenetic data also show that the genus Rymovirus contains at least two unique evolutionary lineages. Thus the current taxonomy, based on transmission vector, is paraphyletic. We present an analysis of the taxonomic relationships among members of the family and propose a classification that both resolves the paraphyly and more accurately represents the evolutionary history of the Potyviridae.

Genetic Variability Among Maize Inbred Lines for Resistance to the High Plains Virus-Wheat Streak Mosaic Virus Complex.

High plains virus (HPV) is a pathogen that causes a severe disease, especially in susceptible corn genotypes. The virus is transmitted by the eriophyid mite Aceria tosichella, which also transmits wheat streak mosaic virus (WSMV). This often results in a mixed infection by these two viruses. Genetic variability for resistance to the HPV exists among maize inbred lines but has not been characterized. The disease reaction of 30 maize inbred lines to the mixed infection and to WSMV alone was characterized in this study. Evaluation was based on symptom expression and virus titer (HPV and WSMV), as measured by enzyme-linked immunosorbent assay. All lines showed some HPV symptoms, which ranged from a few visible spots to rapid plant death. HPV-resistant inbreds include B73 and B14. Susceptible inbreds include W64A, Wf9, H100, N213, N215, and N194. Five of the six inbreds most severely affected by HPV also had a high WSMV titer, although they displayed few symptoms when inoculated with WSMV alone. Inbred N194 was one of the genotypes most susceptible to HPV, but it showed no detectable WSMV titer. Seedlings of highly susceptible genotypes often died within 2 weeks of infection.

A viewpoint on the taxonomy of potyviruses infecting sugarcane, maize, and sorghum.

The value of taxonomy lies in its ability to communicate concepts and relationships. Our present concepts of the poaceous potyviruses, based on their biology, serology, and biochemistry, identify four viruses that can be distinguished by each characteristic. Identifying these as four distinct viruses has important implications for disciplines such as epidemiology, plant breeding, and diagnostics.