CIVETAN   23983
CENTRO DE INVESTIGACION VETERINARIA DE TANDIL
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
HERPES VIRUS BOVINO TIPO 1 EN EL SISTEMA NERVIOSO DE TERNEROS INFECTADOS EXPERIMENTALMENTE
Autor/es:
MARIN, M; MORÁN, P; ODEÓN, A; PEREZ, S. E
Lugar:
Tandil
Reunión:
Congreso; IX REUNION ARGENTINA DE PATOLOGIA VETERINARIA 2014; 2014
Resumen:
Bovine herpesvirus type 1 (BoHV-1) is an
alpha-herpesvirus responsible for respiratory and genital disease in cattle. Encephalitis
by BoHV-1 is only occasionally reported. This condition is mainly attributed to
the closely related alpha-herpesvirus, BoHV-5. However, it has been recently demonstrated
that the participation of BoHV-1 in neurological disease is not a rare event,
as previously thought. In this study, the distribution and the pathological alterations caused by two BoHV-1 strains
in the nervous system of experimentally infected calves during primary (acute)
infection are described. For this study, 6 crossbred, 6 months to 1 year old
calves were used. Animals were free of detectable antibodies to BoHV-1 or
BoHV-5. The results presented are gathered from two independent experiments,
performed with different purposes. Calves were intranasally inoculated with
BoHV-1 Los Angeles (LA) strain (Experiment 1) or Cooper strain (Experiment 2). To
establish comparisons between experiments, in this analysis animals were
grouped as follows: Group 1 (4 calves) for the study of primary infection. Calves
in this group were inoculated with 106.3 tissue culture infective
doses (TCID50) of LA (2 calves, 25ml inoculum) or Cooper (2 calves, 10
ml inoculum) strains; Group 2 consisted of two mock-infected calves, which were
inoculated with culture medium as placebo. Euthanasia was performed at 6 (2
Cooper strain-inoculated calves and 1uninfected calf) and 7 days
post-inoculation (dpi) (2 LA-inoculated calves and 1uninfected calf). Nasal and
ocular secretions were collected on 0, 4, 5 and 6 dpi. After euthanasia, 1-2 cm-thick
sections of the brain were collected aseptically and individually for virus
isolation, PCR and histopathology. The following areas were evaluated: anterior
cerebral cortex, including the olfactory cortex (sample 1), frontal cortex
(samples 2 and 3) and dorso-lateral cortex (sample 4); posterior cerebral
cortex, including the marginal groove area (sample 5) and the ectomarginal
groove area (sample 6); cerebellum (sample 7); cervical medulla (sample 8);
medulla oblongata (sample 9), pons (sample 10) and diencephalon (sample 11).
Furthermore, trigeminal ganglia (TG) were also collected. During primary infection with LA strain, the presence of nasal secretions
was observed in one calf at 4 dpi and in both inoculated calves at 6 dpi.
Ocular secretions were intermittently detected. For calves inoculated with
Cooper strain, nasal secretions were detected at 1, 3, 4 and 5 dpi. Ocular
secretions were also evident during the period evaluated. Differences in rectal
temperatures were recorded at 4 to 6 dpi for animals inoculated with LA strain,
when compared with mock-infected calves (P <0.05). Significant differences
between Cooper strain- and mock-infected calves were not detected (P >0.05).
Neurological signs were not observed in animals from any experiment. However, in
calves inoculated with LA strain, the virus was isolated from all tissue
sections (samples 1 to 11 and TG) of both experimentally inoculated calves. In
some samples, the amount of infectious virus was too low to determine the viral
titer. For Cooper-infected calves, it was also possible to isolate the virus
from all brain sections, with the exception of cervical medulla. TG was also
negative for virus isolation. In comparison with the findings for
Cooper-infected calves, virus titers in neural tissues for LA-inoculated
animals were 3 to 4 log lower. As
expected, virus was not isolated from mock-infected calves. In calves
inoculated with Cooper strain, at 6 dpi, viral DNA was detected in frontal and
posterior cortex, cervical medulla, medulla oblongata and TG. Similar
distribution of virus DNA was observed for LA-infected calves. In any case virus
genome was not detected in pons or diencephalon and it was not detected in
samples from uninfected calves, as expected. Macroscopic lesions were not
evident in calves from any group. Microscopic observation of neural tissue from
LA-infected calves revealed focal hemorrhages in all brain areas. Furthermore,
mild non-suppurative meningitis was evident in these calves. Mononuclear
perivascular cuffings and focal gliosis were present in anterior and posterior
cortex and medulla oblongata. Diffuse gliosis was present in anterior and
posterior cortex and areas of neuronophagia and satellitosis were detected in
the cortex, base of the brain and diencephalon. Microscopic lesions were not
observed in TG. In Cooper-infected calves relevant microscopic lesions were not
observed. An important finding from these experiments is the fact that, like
BoHV-5, BoHV-1 is able to replicate and disseminate within the nervous tissue. It
is also apparent that there are differences in the ability of the strains to
replicate and induce microscopic lesions in the brain. Nevertheless, future
studies will be required to determine the molecular aspects that prevent the
development of clinical encephalitis in BoHV-1-infected cattle.