Progress in medical virology. Fortschritte der medizinischen Virusforschung. Progres en virologie medicale最新文献

'The simplest of all virus disease is measles' said Kenneth Maxy 40 years ago in a chapter on epidemiology. I hope that the data set out here provide the reader with a sufficiently complete and clear picture of the factors that determine measles epidemiology, that he or she will agree with Maxy's prescient words. Measles is an antigenically complex virus, but few components of the immune response to this virus are epidemiologically relevant. The relevant components are durable for a lifetime. They can be conveniently measured by serological tests, and the results of these tests correlate well with measles immunity. The tests show that measles is an extremely infectious disease, and that very high antibody prevalence rates are needed for herd protection. The currently available measles vaccine is capable of yielding adequate antibody prevalence rates for herd immunity, but to achieve this, immunization procedural flaws and faulty records must be kept to very low levels. The greatest obstacle to worldwide control of measles is a failure of vaccination programs to produce adequate herd immunity levels in less-developed countries. There, vaccine must be given promptly after passive immunity wanes, because the level of endemicity is so high. It is difficult to determine just what age is optimal, because it varies from one country to another. Premature vaccination not only fails to immunize, but also interferes with subsequent re-immunization. Because we now know this, further direct tests of vaccine effectiveness in very young children are ethically undesirable, and methods that use determination of passively acquired antibody are to be preferred. The levels of antibody that mothers have to pass to their children vary considerably. These differences are important in comparisons of South Asian countries with others, but not elsewhere. Differences in efficiency of transport of antibody across the placenta also play a role, but usually a minor one. Most important seems to be variation in antibody durability in the infant. Where families are poor, the children acquire many infections at an early age, and passively acquired antibody is swept out. These children who are least able to withstand the effects of measles infection, are hit at the earliest age. To provide protection for them, the vaccine must be given at a carefully determined age, specific for each community. Only when this is done can we hope to reduce measles worldwide to a sufficiently low level that it will be removed as a threat to persons in the United States, or anywhere else.

Hantaviruses, the causative agents of HFRS, have become more widely recognized. Epidemiologic evidence indicates that these pathogens are distributed worldwide. People who come into close contact with infected rodents in urban, rural and laboratory environments are at particular risk. Transmission to man occurs mainly via the respiratory tract. The epidemiology of the hantaviruses is intimately linked to the ecology of their principal vertebrate hosts. Four distinct viruses are now recognized within the hantavirus genus and that number is likely to increase to six very soon; however, further investigations are necessary. Much more work is still needed before we fully understand the wide spectrum of clinical signs and symptoms of HFRS as well as the pathogenicity of the different viruses in the hantavirus genus of the Bunyaviridae family. HFRS is difficult to diagnose on clinical grounds alone and serological evidence is often needed. A fourfold rise in IgG antibody titer in a 1-week interval, and the presence of the IgM type of antibodies against hantaviruses are good evidence for an acute hantavirus infection. Physicians should be alert for HFRS each time they deal with patients with acute febrile flu-like illness, renal failure of unknown origin and sometimes hepatic dysfunction. Especially the mild form of HFRS is difficult to diagnose. Acute onset, headache, fever, increased serum creatinine, proteinuria and polyuria are signs and symptoms compatible with a mild form of HFRS. Differential diagnosis should be considered for the following diseases in the endemic areas of HFRS: acute renal failure, hemorrhagic scarlet fever, acute abdomen, leptospirosis, scrub typhus, murine typhus, spotted fevers, non-A, non-B hepatitis, Colorado tick fever, septicemia, dengue, heartstroke and DIC. Treatment of HFRS is mainly supportive. Recently, however, treatment of HFRS patients with ribavirin in China and Korea, within 7 days after onset of fever, resulted in a reduced mortality as well as shortened course of illness.

Until recently, it has been generally assumed that all human viruses are causative agents of diseases and should be regarded as harmful pathogenic agents that require control measures. In the early 1950s we began to doubt this view. In the course of experiments on virus isolations from feces of normal children, as well as in studies of isolates from animals and from tissue cultures, data accrued which suggested that some conditionally pathogenic and some completely nonpathogenic strains of enteroviruses may provide some benefit to their host by inhibition of pathogenic viruses and by activating nonspecific protective functions of the organism. The novel concept of beneficial viruses was proposed which suggested that the process of co-evolution of the host organism and its associated viral flora led to a specific interaction between them that was beneficial for both. This concept provides a potential approach to the nonspecific prevention of viral diseases by means of the interference between beneficial enteroviruses and pathogenic viruses belonging to different classes.