Emerging infectious diseases in the 21st century

Potential for the replication of the betanodavirus redspotted grouper nervous necrosis virus in human cell lines

The determination of the host ranges of viruses is important because of the possible emergence of infectious agents, which may result from the zoonotic transmission of animal viruses to humans. The family Nodaviridae, whose members are non-enveloped, positive-stranded bipartite RNA viruses, is comprised of the genera Alphanodavirus and Betanodavirus, whose members predominantly infect insects and fish, respectively. The alphanodaviruses can also infect suckling mice and suckling hamsters, resulting in paralysis and death. Pigs near the site of isolation of the Nodamura virus (NoV), an alphanodavirus, have been reported to have high levels of NoV neutralizing antibody, suggesting that they may be part of the natural host range of this virus. Betanodaviruses are the causative agents of viral nervous necrosis, which occurs in several species of fish. However, little is known regarding the mechanism of infection of these viruses. Whether betanodaviruses can infect hosts other than fish remains unclear. In this study, we examined the possibility that a betanodavirus, redspotted grouper nervous necrosis virus (RGNNV), can infect human cell lines and showed that this virus can attach to the cells but cannot penetrate them, although human cells can support the replication of the betanodavirus when viral RNAs are transfected. The betanodavirus in its present form cannot infect human cells.

Cross-species transfer of viruses: implications for the use of viral vectors in biomedical research, gene therapy and as live-virus vaccines

All living organisms are continuously exposed to a plethora of viruses. In general, viruses tend to be restricted to the natural host species which they infect. From time to time viruses cross the host-range barrier expanding their host range. However, in very rare cases cross-species transfer is followed by the establishment and persistence of a virus in the new host species, which may result in disease. Recent examples of viruses that have crossed the species barrier from animal reservoirs to humans are hantavirus, haemorrhagic fever viruses, arboviruses, Nipah and Hendra viruses, avian influenza virus (AI), monkeypox virus, and the SARS-associated coronavirus (SARS-CoV). The opportunities for cross-species transfer of mammalian viruses have increased in recent years due to increased contact between humans and animal reservoirs. However, it is difficult to predict when such events will take place since the viral adaptation that is needed to accomplish this is multifactorial and stochastic. Against this background the intensified use of viruses and their genetically modified variants as viral gene transfer vectors for biomedical research, experimental gene therapy and for live-vector vaccines is a cause for concern. This review addresses a number of potential risk factors and their implications for activities with viral vectors from the perspective of cross-species transfer of viruses in nature, with emphasis on the occurrence of host-range mutants resulting from either cell culture or tropism engineering. The issues are raised with the intention to assist in risk assessments for activities with vector viruses.

Advocacy, promotion and e-learning: Supercourse for zoonosis

This paper discusses the history of emerging infectious diseases, risk communication and perception, and the Supercourse lectures as means to strengthen the concepts and definition of risk management and global governance of zoonosis. The paper begins by outlining some of the key themes and issues in infectious diseases, highlighting the way which historical analysis challenges ideas of the 'newness' of some of these developments. It then discusses the role of risk communication to public accountability. The bulk of the paper presents an overview of developments of the Internet-based learning system through the Supercourse lectures that may prove to be a strong arm for the promotion of the latest medical information particularly to developing countries.

The challenge of emerging and re-emerging infectious diseases

Infectious diseases have for centuries ranked with wars and famine as major challenges to human progress and survival. They remain among the leading causes of death and disability worldwide. Against a constant background of established infections, epidemics of new and old infectious diseases periodically emerge, greatly magnifying the global burden of infections. Studies of these emerging infections reveal the evolutionary properties of pathogenic microorganisms and the dynamic relationships between microorganisms, their hosts and the environment.

[Multilocus sequence typing: the molecular marker of the Internet era]

Global or longer term epidemiology track the spread of clonal lineages, associated with hipervirulence or resistance or multi-resistance to antimicrobial agents. Therefore, the application of a molecular typing system for this purpose should produce data easily shared by different and geographically distant laboratories, as well as distinguish those clonal lineages even with low levels of variability accumulated in the genome.A marker based on the DNA sequence will produce objective results easily organized in data bases accessible by Internet. The application of a similar strategy that was used in the analysis of isoenzymes, by sequencing variable fragments of selected housekeeping genes, will allow obtaining a general view of the distribution of the clonal lineages and tracking their spread.

A 10-year survey of Mycobacterium tuberculosis isolates in Pavia and their drug resistance: a comparison with other Italian reports

A retrospective review was made of the bacteriological and medical records of patients with culture-confirmed pulmonary tuberculosis who attended the IRCCS San Matteo Polyclinic of Pavia, between 1990 and 2000. Altogether, 279 patients were included in the survey: 220 new cases and 59 prior treatment cases. Resistance to at least one drug, and resistance to both isoniazid and rifampicin (MDR) were more common among previously treated patients than among new cases (86.4% vs. 34.1%, and 44% vs. 5.9%, respectively). While the frequency of resistance to any drug showed no variation in the period examined, a trend toward a progressive decrease in the frequency of primary MDR-TB was observed (from 11.9% in 1990-1992 to 1.3% in 1998-2000). The level of resistance observed in our study suggests that all isolates of Mycobacterium tuberculosis should be tested for drug susceptibility, especially when obtained from patients who report a previous episode of the disease.

Risk factors for human disease emergence

A comprehensive literature review identifies 1415 species of infectious organism known to be pathogenic to humans, including 217 viruses and prions, 538 bacteria and rickettsia, 307 fungi, 66 protozoa and 287 helminths. Out of these, 868 (61%) are zoonotic, that is, they can be transmitted between humans and animals, and 175 pathogenic species are associated with diseases considered to be 'emerging'. We test the hypothesis that zoonotic pathogens are more likely to be associated with emerging diseases than non-emerging ones. Out of the emerging pathogens, 132 (75%) are zoonotic, and overall, zoonotic pathogens are twice as likely to be associated with emerging diseases than non-zoonotic pathogens. However, the result varies among taxa, with protozoa and viruses particularly likely to emerge, and helminths particularly unlikely to do so, irrespective of their zoonotic status. No association between transmission route and emergence was found. This study represents the first quantitative analysis identifying risk factors for human disease emergence.