Virus replication and ultrastructural changes after induction of encephalitis in mice by measles virus

Intensive Exposure as a Risk Factor for Severe Polio: A Study of Multiple Family Cases

To examine the importance of intensity of exposure for the outcome of the poliomyelitis infection 429 polio cases were identified belonging to families with 2, 3 or 4 polio cases, all hospitalized in Copenhagen from 1919 to 1953. Furthermore, 87 pairs of polio cases living on the same stairway, but not in the same household, were identified. Severity among multiple cases in families analysed according to time of appearance showed a U-shaped curve. Initial cases had a higher risk of developing paralysis [relative risk (RR) = 1.5, 95% confidence interval (CI) 1.2-1.91 and of dying (RR = 2.5, 95% CI 0.9-6.9). Decreased severity was observed among subsequent cases appearing within 11 d after the initial case (RR = 1.0); however, severity increased again, with higher mortality for cases likely to have been infected by the initial case (cases appearing more than 11 d later) (RR = 5.7, 95% CI 1.8-17.8). The pattern described among multiple family cases was not found among cases from the same stairway. Since family cases appearing within 11 d were probably infected simultaneously, a short incubation period is associated with severe disease and a prolonged incubation period with milder infections. Furthermore, intensive exposure from being infected in the household increased severity. These observations therefore suggest that intensity of exposure and dose of infection are important factors in the severity of poliomyelitis.

Patterns of exposure and severity of measles infection. Copenhagen 1915-1925

Using data on children hospitalized with measles in Copenhagen from 1915 to 1925, I found that secondary cases (infected at home) exposed to two or more index cases had a higher case fatality rate than did children exposed to a single index case (relative risk (RR) = 1.90; 95% confidence interval (CI): 1.12 to 3.22). Compared with surviving cases, fatal secondary cases had a shorter interval between their own rashes and rash in the index case (P < .02), suggesting a shorter period of incubation for severe cases. Secondary cases infected by a severe case of measles had higher mortality (RR = 3.87; 95% CI: 1.65 to 9.08) than did secondary cases infected by an index case without pneumonia. These observations suggest that differences in patterns of exposure, possibly due to the dose of infection, may be important for understanding variation in measles mortality.

High measles mortality in infancy related to intensity of exposure

In a West African urban community, measles infection in infants was examined over 5 years (1979-1983). In the age group 0 to 11 months, measles mortality was higher among secondary cases (infected in the house) than among index cases (infected outside the house), and the proportion of secondary cases was significantly higher for this age group than for older children. Intensive exposure related to the social pattern of disease transmission may be important in explaining the high infant mortality observed with measles in developing countries. Mortality during the first 12 months of life increased with age, presumably because of the decrease of maternally derived measles antibodies. In children younger than 6 months of age, who are usually considered to be protected by maternal antibody, intensive exposure may lead to infection, as demonstrated by a high level of measles-specific antibodies in some children exposed to an older sibling with measles. The aim of public health policies should be to change conditions of exposure.

Severe measles: a reappraisal of the role of nutrition, overcrowding and virus dose

The factors predisposing to severe measles, which accounts for a considerable fraction of the high infant and child mortality in the third world, are re-examined. The conviction that protein-energy-malnutrition (PEM) aggravates measles is challenged by findings of prospective community-based studies. It was found that severe measles was not associated with PEM but frequently accompanied overcrowding in Guinea-Bissau. Secondary cases fared worse than index patients. Among adequately nourished hospitalised African children, immunological and radiological parameters, together with the effects of age and HLA antigens, were closely related to sickness and death in measles. This variation in case fatality rate does not appear to be simply explained by age-dependent host reactions or differences in medical care. The hypothesis which fits most of the observed facts postulates that the transmission of a large inoculum of virus particles to susceptible children is an important cause of severe disease. The implication of this interpretation is that specific measles control, and not only improvements in nutrition, is important in high risk areas for a reduction of measles mortality. It is further suggested that health policy should promote those social changes which limit intense exposure to measles virus.

CNS disease following dissemination of SSPE measles virus from intraperitoneal inoculation of suckling hamsters

Acute encephalitis was observed in suckling Golden Syrian hamsters following intraperitoneal (ip) inoculation of a hamster brain adapted strain of subacute sclerosing panencephalitis (SSPE) measles virus (HBS). Virus was isolated from the brains of all encephalitic animals by cocultivation of tissue with Vero cells. The histopathology of the encephalitis was characterized by perivascular mononuclear infiltrates, necrosis, eosinophilic inclusion bodies, and rare giant cells. Association of encephalitis with systemic viral infection was observed with virus present in lung and a kidney-spleen pool in addition to brain. Viral dissemination in asymptomatic animals was documented with virus being isolated from multiple non-neural tissues (spleen, lung, liver) of animals having no recoverable virus in their brains and no signs of encephalitis. Treatment of animals with cyclophosphamide prior to ip virus inoculation did not increase dissemination to brain. Absence of encephalitis in asymptomatic animals with proven viral dissemination to parenchymal organs indicates that neither viremia alone, nor viremia in conjunction with dissemination are sufficient conditions to establish central nervous system disease. The association of encephalitis with systemic viral infection and the dissemination to brain establish this model's potential value for the study of the pathogenesis of measles encephalitis.

SSPE-like inclusion body disorder in treated childhood leukemia

Clinico-pathological report on a boy with cytostatically treated leukemia, dying with cerebral symptoms after passing clinical measles 10 weeks before death. At autopsy, numerous nuclear inclusion bodies in glial and nerve cells were found. By electron microscopy, nuclear inclusions appeared as loosely arranged smooth tubules, corresponding to paramyxovirus nucleocapsids. Frequently, cytoplasmic changes appeared too, consisting of incomplete tubular structures and an abundant dense "fuzzy" material. No regular tubuli of the coated granular type were present, as in common measles virus infection, nor any mature viral structures or differentiation of the surface membrane. The lack of maturation in cytoplasm together with a predominance of nuclear changes suggested a slow type of measles virus infection, while the particular cytoplasmic changes suggested a defect in synthesis of granular nucleocapsids, possibly a basic factor for the slow type of the viral infection. Possible pathogenetic factors are discussed.

Ultrastructural study of long-term measles infection in cultures of hamster dorsal-root ganglion

The morphogenesis of the Edmonston strain of measles is described in cultures of hamster dorsal-root ganglion maintained for as long as 63 days postinoculation. The patterns observed confirmed those previously reported in both neural and non-neural tissue. However, in the present tissue, the development of viral material could be followed chronologically within different cell types such as neurons and Schwann cells. Active replication was visualized up to 63 days postinoculation. The appearance of cytoplasmic nucleocapsid preceded that of intranuclear nucleocapsid, the latter occurring after 14 days. These intranuclear inclusions were formed after the transformation of the nucleoli into bizarre pleomorphic bodies which eventually segregated into clumps of nucleocapsid. These intranuclear inclusions mimic those seen in subacute sclerosing panencephalitis, now known to be etiologically related to a measles-like virus.

Ultrastructure of measles virus in cultures of hamster cerebellum

Replication of Edmonston strain of measles virus in cultures of hamster central nervous system tissue was studied by electron microscopy of ultrathin sections. Infected cultures were fixed from 3 hr to 39 days postinoculation (PI). Measles nucleocapsid was first seen within the cytoplasm of giant cells, the latter appearing 5 to 6 days PI. Measles virus particles were most abundant at 10 days PI and appeared to bud off from areas of the cell membrane along which nucleocapsid was aligned. Intranuclear nucleocapsid was more abundant at later stages, and by 39 days PI entire nuclei were seen to be occupied. By this time, the cytoplasmic formations, which had been sequestered by membranes, appeared to lose their regular structure. Budding viral particles at 39 days PI were of a much simplified structure and did not involve the alignment of nucleocapsid about their periphery.