Morumbi virus is a member of Phlebotomus Fever serogroup
(Bunyaviridae family, Phlebovirus genus), native from the Brazilian Amazon region.
It'svector is unknown, but is supposed to be, transmitted by phlebotomine sandflies.
It was isolated in 1988 from a human presenting an acute febrile illness. When
inoculated in the brain of Newborn Swiss mice, this arbovirus showed visceral
tropism, including liver damage. In order to establish the anatomopathological and
immunohistochemical characteristics in the liver of albino Swiss suckling mice
experimentally infected with Morumbi virus; to assess the differences of tropism of
the virus in the liver following the intra cerebral, intra peritoneal or subcutaneous
routes of inoculation; to detail the sequence of anatomical and pathological events in
the liver; to demonstrate the location of the viral antigen in the hepatic tissue during
the experimental assay; and to study the possible relationship between the
anatomopathological and immunohistochemical findings, an experimental study was
conducted with 71 Newborn Swiss mice (two or three days of age), distributed as
follows: 21 received intra cerebral inoculation (IC), 21 received intraperitoneal
inoculation (IP) and 29 received subcutaneous inoculation (SC). 0.02ml of virus
suspension was used as the infectious dose. The control was comprised of 30 mice
that were not inoculated. Subgroups of 8 mice (6 inoculated, 2 controls) were
euthanized daily, at intervals of 24 - 96 hours in the IC and IP groups, and until 120
hours in the SC group. Liver specimens from all mice were fixed in a 10% neutral
formalin solution, then embedded in paraffin wax to obtain 5f.lm sections that were
stained with haematoxylin/eosin for morphological analysis. Immunohistochemical
technique (Envision System, DAKO, USA) was employed in additional sections,
using alkaline phosphatase and hyper-immune anti-Morumbi virus serum prepared
into suckling mice, to detect the viral antigen. 6 patterns of portal lesion and 9
patterns of lobule lesion were studied in a scale from zero (0) to three (+++), where
zero represented absence of lesion and three represented severe lesion. Light
microscopy examination revealed that Morumbi virus was able to produce hepatic
lesions in the portal and lobular areas when inoculated in mice in three different
routes, raising an acute hepatitis, in which bodies similar to Councilman - Rocha
Lima bodies were observed, irregularly distributed in the lobules. The appearance of
those bodies occurred 24 hours post-inoculation (pi), with a peak at 72 hours pi in
miceis inoculated. The immunohistochemical technique showed mild presence of
viral antigen from 24 hours after inoculation in IC group and from 48 hours after in IP
and SC groups, showing a certain parallelism between the detection of viral antigens
and the morphological lesions. Maximum detection of the viral antigen was observed
in IP rout, specially those mice euthanized at 72 hours pi. General distribution of the
antigen was concentrated in the hepatic lobules, in the cytoplasm of normal and
necrotic hepatocytes, as well as inside the Kupffer cells, without any preference for
the three lobule areas. The following conclusions are made: i) experimentally
infected mice model was excellent to study the Morumbi virus-induced lesions, with
preference to IP rout; ii) in all inoculated routes (IP, IC and SC) there were evidence
of Morumbi virus infection, with a remarkable detection of its antigen in the hepatic
tissue of Swiss mice; iii) Morumbi virus antigen detected in the liver of Swiss mice
was associated with acute hepatitis and with focal necrosis; iv) an intense acute
hepatitis occurred in the liver of euthanized mice 72 hours pi with Morumbi virus by
the intraperitoneal route but was not observed in the other two used routes; v) in this
experiment, acute hepatitis was limited, showing a clear tendency to disappear in the
follow up in the majority of inoculated animals; vi) cholestasis was not very often
observed in the experimental hepatitis due to Morumbi virus; vii) Morumbi virus
antigen was detected predominantly in the cytoplasma and was exhibiting a granular
pattern in hepatocytes and Kupffer cells; viii) Morumbi viral antigen was detected as
early as 24 hours in hepatic tissue in IC route and 48 hours after IP and SC routes.
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