Venezuelan Equine Encephalomyelitis Virus Infection Research Articles

Melatonin decreases nitric oxide production and lipid peroxidation and increases interleukin‐1 beta in the brain of mice infected by the Venezuelan equine encephalomyelitis virus

Melatonin, a potent antioxidant, has shown to be beneficial in murine Venezuelan equine encephalomyelitis (VEE) virus infection. In addition, melatonin can induces the production of interleukin-1 beta (IL-1beta), a cytokine capable of inducing increased expression of inducible nitric oxide synthase; the activity of this enzyme is increased in the brain of mice infected with VEE virus. The aim of this study was to determine the effect of VEE virus on the nitric oxide (NO) production, lipid peroxidation and IL-1beta production in the brain and serum of mice infected with VEE virus, and to investigate the modulatory role of melatonin during this viral infection. Mice were infected with 10 LD(50) of VEE virus and treated with melatonin (500 microg/kg of body weight) starting 3 days before and continuing for 5 days after virus inoculation. Mice were sacrificed on days 1, 3 and 5 postinfection and brains and blood samples were obtained. NO and IL-1beta production and lipid peroxidation levels were measured in perfused brain homogenates and serum. Increased production of brain nitrite was found on days 1, 3 and 5 postinfection and lipid peroxidation products were increased at day 5. Levels of serum nitrite were found elevated on days 3 and 5 postinfection; however, lipid peroxidation products remained similar to basal levels. Melatonin treatment decreased nitrite concentration in brain and serum of infected mice as well as the lipid peroxidation products in the brain. IL-1beta was found to be increased in the brain and serum of infected animals, and melatonin treatment induced higher levels of this cytokine (brain: about 4-fold; serum: about 8-fold). These results may be related to the beneficial effect of melatonin in the VEE experimental disease and address the possible therapeutic potential of the indoleamine in human VEE virus infection.

Melatonin and viral infections.

: The therapeutic effects of melatonin against viral infections, with emphasis on the Venezuelan equine encephalomyelitis (VEE), are reviewed. Melatonin has been shown to prevent paralysis and death in mice infected with the encephalomyocarditis virus and to decrease viremia. Melatonin also postpones the onset of the disease produced by Semliki Forest virus inoculation and reduces the mortality of West Nile virus‐infected mice stressed by either isolation or dexamethasone injection. An increase in the host resistance to the virus via a peripheral immunostimulatory activity is considered responsible for these effects. It has also been demonstrated that melatonin protects some strains of mink against Aleutian disease, and prevents the reduction of B‐ and T‐cells as well as Th1 cytokine secretion in mice infected with leukemia retrovirus. In VEE‐infected mice, melatonin postpones the onset of the disease and death for several days and reduces the mortality rate. This protective effect seems to be due to the increase in the production of interleukin‐1β (IL‐1β), as 100% of the infected mice treated with melatonin die when IL‐1β is blocked with antimurine IL‐1β antibodies. Although melatonin administration raises serum levels of tumor necrosis factor‐alpha (TNF‐α) and interferon‐gamma (IFN‐γ), the mortality observed in neutralization experiments with the corresponding anticytokine antibodies, suggests that neither TNF‐α nor IFN‐γ are essential for the protective effect of melatonin on murine VEE virus infection. Melatonin treatment also enhances the efficiency of immunization against the VEE virus. Reactive oxygen species have been implicated in the dissemination of this virus, and their deleterious effects may be diminished by melatonin. This indole inhibits nitric oxide synthetase activity and it is a potent scavenger of nitric oxide, which also plays an important role in the spread of the VEE virus. In conclusion, the immunomodulatory, antioxidant, and neuroprotective effects of melatonin suggest that this indole must be considered as an additional therapeutic alternative to fight viral diseases.

Melatonin increases interleukin-1beta and decreases tumor necrosis factor alpha in the brain of mice infected with the Venezuelan equine encephalomyelitis virus.

The effect of melatonin (MLT) on the brain levels of tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in Venezuelan equine encephalomyelitis (VEE) virus infection was determined. Brain homogenates from mice inoculated with 10 LD50 of VEE virus, untreated or treated with 500 microg MLT/kg body weight were assayed by ELISA to measure the levels of TNF-alpha and IL-1beta. MLT was injected daily starting 3 days before and continuing to 7 days after virus inoculation. Infected mice treated with MLT showed decreased levels of TNF-alpha when compared to the untreated infected mice on days 1, 3, 4, and 5 postinoculation (P < 0.001). In contrast, IL-1beta levels increased from days 1 to 5 in the infected mice treated with MLT when compared with the untreated infected animals (P < 0.01). The results suggest that the protective effect of MLT on the VEE virus infection could be due, among other factors, to a decrease in TNF-alpha synthesis along with an increase in the production of IL-1beta.

Vector competence of Peruvian mosquitoes (Diptera: Culicidae) for epizootic and enzootic strains of Venezuelan equine encephalomyelitis virus.

Mosquitoes collected in the Amazon Basin, near Iquitos, Peru, were evaluated for their susceptibility to epizootic (IAB and IC) and enzootic (ID and IE) strains of Venezuelan equine encephalomyelitis (VEE) virus. After feeding on hamsters with a viremia of approximately 10(8) plaque-forming units of virus per milliliter, Culex (Melanoconion) gnomatus Sallum, Huchings, & Ferreira, Culex (Melanoconion) vomerifer Komp, and Aedes fulvus (Wiedemann) were highly susceptible to infection with all four subtypes of VEE virus (infection rates > or = 87%). Likewise, Psorophora albigenu (Peryassu) and a combination of Mansonia indubitans Dyar & Shannon and Mansonia titillans (Walker) were moderately susceptible to all four strains of VEE virus (infection rates > or = 50%). Although Psorophora cingulata (Fabricius) and Coquillettidia venezuelensis (Theobald) were susceptible to infection with each of the VEE strains, these two species were not efficient transmitters of any of the VEE strains, even after intrathoracic inoculation, indicating the presence of a salivary gland barrier in these species. In contrast to the other species tested, both Culex (Melanoconion) pedroi Sirivanakarn & Belkin and Culex (Culex) coronator Dyar & Knab were nearly refractory to each of the strains of VEE virus tested. Although many of the mosquito species found in this region were competent laboratory vectors of VEE virus, additional studies on biting behavior, mosquito population densities, and vertebrate reservoir hosts of VEE virus are needed to incriminate the principal vector species.

Venezuelan Equine Encephalomyelitis Virus Infection in and Transmission by the Tick Amblyomma cajennense (Arachnida: Ixodidae)

To assess a possible role of ticks as the maintenance host for epizootic strains of Venezuelan equine encephalomyelitis (VEE) virus, laboratory experiments were conducted to determine if ticks could become infected, maintain, and transmit the virus. Larval and nymphal Amblyomma cajennense (F.) and larval Dermacentor nitens Neumann ticks were exposed to epizootic VEE virus (Trinidad donkey strain) by allowing them to feed on viremic guinea pigs (strain 13). In A. cajennense, transstadial transmission was observed from larvae to nymphs and adults. Horizontal viral transmission to a mammalian host was accomplished by nymphs. Infection rates in nymphs and adults were 2% (42/2,750) and 4% (9/244), respectively, afer ingestion of virus as larvae. Virus was detected in A. cajennense adult ticks for up to 171 d after infection in the larval stage. A cajennense, exposed as nymphs, ingested virus but did not become infected (0/164 after 10 d after taking an infective bloodmeal). No virus was detected in D. nitens 7 d after exposure. These findings suggest that A. cajennense potentially could be involved in an interepizootic maintenance cycle of epizootic VEE viral strains.

RNa-polymerase, type I: Activity in rat brain cell nuclei and peripheral blood mononuclear cells after Venezuelan Equine Encephalomyelitis virus infection

Rats inoculated intraperitoneally with 100 LD50 of Venezuelan Equine Encephalomyelitis virus (VEE), showed a significant decrease of DNA-dependent RNA polymerase type I activity of brain nuclei of 29.7% and 59.3% at 24 and 48 hours after infection, respectively, while the animals had no clinical symptoms of illness. No alterations were observed in the nuclei of mononuclear cells at any time. VEE virus titer was higher in the serum than in the brain. The results suggest that viral infection produced a modification in the activity of this enzyme only in brain, even with a low amount of virus, and had no effect on enzyme activity of mononuclear cells.

Changes in serum and striatal free amino acids after Venezuelan equine encephalomyelitis virus infection

The infection with the Venezuelan equine encephalomyelitis virus produced a significant increase in the concentration of alanine, arginine, asparagine, glutamine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan, tyrosine, and valine in the striatum of rats. On the contrary, the concentrations of aspartate, GABA, glutamate, and taurine were reduced. Arginine, aspartate, glycine, methionine, phenylalanine, taurine, and tyrosine concentrations were increased in the serum of infected rats. However, the modifications in the content of free amino acids in the striatum and serum of rats that survived the infection were qualitatively and quantitatively different from those detected during the acute phase of the infection.

Role of complement and the Fc portion of immunoglobulin G in immunity to Venezuelan equine encephalomyelitis virus infection with glycoprotein-specific monoclonal antibodies

We have previously characterized with monoclonal antibodies (MAbs) seven unique epitopes on the two envelope glycoproteins of Venezuelan equine encephalomyelitis (VEE) virus vaccine strain TC-83. The epitopes important in protection from VEE virus infection were determined in passive antibody transfer studies, with virulent VEE (Trinidad donkey) virus as the challenge virus. Selected high-avidity MAbs to the three major protective epitopes (E2c, E1b, and E1d) were assayed for in vitro complement activity. All three fixed murine complement to high titer. Limited pepsin digestion of the anti-E2c in the presence of cysteine resulted in a rapid decrease and complete loss of complement-fixing ability by 2 h, but the majority of mice, except at the lowest dilution of MAb, were protected until the Fc termini were cleaved at 3 h. Anti-E2c F(ab')2 would neutralize VEE (Trinidad donkey) virus more efficiently than either Fab' or Fab; none of the fragments would fix complement or was effective in passive protection. C5-deficient mice and mice depleted of C3 with cobra venom factor were still protected from VEE (Trinidad donkey) virus challenge after passive transfer of either anti-E2c or anti-E1b MAb. The results show that the anti-E2c MAb mediates neutralization through bivalent binding at a critical site on the virion and that Fc effector functions, other than complement, are necessary for protection. Although the ability of the anti-E2c MAb to fix complement was associated with its ability to protect in vivo, no direct cause-and-effect relationship was found. Since the epitope defined by the anti-E1d antibody is found on the cell membrane, but is not expressed on the infectious virion, protection in mice was most likely mediated at the cellular level, possibly by inhibition of the final stages of virion maturation.

Effect of Venezuelan equine encephalomyelitis virus infection on brain choline acetyltransferase and acetylcholinesterase activities

Mice and rats infected with the Venezuelan equine encephalomyelitis virus showed a significant decrease in the choline acetyltransferase activity of caudate nucleus, hypothalamus, midbrain, hippocampus and frontal cortex. Acetylcholinesterase activity was not affected in any of the same brain regions analyzed. In surviving rats no alterations were observed in the activities of choline acetyltransferase, tyrosine hydroxylase, and glutamate decar☐ylase 3 months after the infection.

Tyrosine hydroxylase activity in Venezuelan equine encephalomyelitis virus infection.

In rats inoculated with the Venezuelan equine encephalomyelitis (VEE) virus, a significant decrease was found in the tyrosine hydroxylase activity of neostriatum, midbrain, and hypothalamus during the acute phase of the infection. In animals that survived the acute infection, we observed no changes in the enzymatic activity in the same regions studied. Our findings suggest a vulnerability of the dopaminergic and noradrenergic pathways to the infection produced by VEE virus.

Central nervous system demyelination in Venezuelan equine encephalomyelitis infection: An experimental model of virus-induced myelin injury

Arboviruses are important pathogens for both animals and humans. Venezuelan equine encephalomyelitis virus (VEEV) is an arbovirus whose pathogenicity for grey matter structures has been previously studied. To our knowledge, the present study is the first to describe extensive inflammation and demyelination in spinal cord white matter of mice infected with VEEV. To probe a possible immunepathogenesis of white matter alterations in this infection, nude mice and heterozygous controls were similarly infected. Whereas controls still showed inflammatory demyelination, nude mice showed no white matter changes in the absence of a mononuclear inflammatory response. These results suggest that white matter changes in VEEV infection are dependent upon the host immune-response, rather than produced by primary viral cytolytic activity. Such findings are similar to those we and others obtained in a number of different viral infections and support the possibility that the host immune response may be the common denominator leading to myelin injury in a variety of viral diseases. The hypothesis of “by-stander killing” of myelin is discussed as a possible host-mediated mechanism of demyelination in viral infections.

GABA metabolism in Venezuelan equine encephalomyelitis virus infection.

Mice infected with the Venezuelan equine encephalomyelitis virus showed a significant decrease in the GABA content of cerebral hemispheres. Activity of the enzyme which synthetizes GABA, glutamate decarboxylase, is also reduced in whole cerebral hemispheres, neostriatum, and frontal cortex of infected animals, as compared to values obtained from the same regions of control mice. No significant difference was demonstrated in the activities of GABA transaminase, glutamate dehydrogenase, lactate dehydrogenase, succinate dehydrogenase and NAD-malate dehydrogenase in any of the regions studied. The results suggest that the viral infection produced an alteration in the mechanism of GABA synthesis.

Interaction of alphaviruses with human peripheral leukocytes: in vitro replication of Venezuelan equine encephalomyelitis virus in monocyte cultures.

Human peripheral blood leukocytes (PBL) were examined for their ability to support growth of several group A arboviruses in vitro. Cells were refractory to infection with eastern (EEE) and western (WEE) equine encephalitis viruses, whereas Venezuelan equine encephalomyelitis (VEE) virus was shown to infect and replicate to a substantially high titer. When PBL were fractionated into purified subpopulations, only the monocytes were susceptible to predictive VEE virus infection. Lymphocytes treated 24 h before virus inoculation with phytohemagglutinin (10 microgram/ml) were capable of propagating significant amounts of VEE virus. A monocytic cell line, J-111, was also susceptible to infection with VEE, EEE, and WEE viruses, whereas a lymphocytic cell line, Raji, was refractory. Additional information on the participation of PBL during human infection with these viruses may add considerably to our understanding of their differing pathogenicities and clinical pictures.

Protective and toxic effects of a nuclease-resistant derivative of polyriboinosinic-polyribocytidylic acid on Venezuelan equine encephalomyelitis virus in rhesus monkeys.

Polyriboinosinic-polyribocytidylic acid, stabilized with poly-L-lysine and carboxymethylcellulose (poly ICLC), favorably alters the pathogenesis of Venezuelan equine encephalomyelitis virus infection in rhesus monkeys by decreasing the number of infected monkey that become detectably viremic and by delaying the onset of viremia in the remaining monkeys. Poly ICLC is known to induce high circulating levels of interferon in primates, and the interferon system is assumed to be the mechanism by which poly ICLC exerts its antiviral effect. Poly ICLC treatment was associated with a few deaths, but only under certain conditions of infection and handling. The death of some infected, treated monkeys in the absence of death in monkeys that were either infected and untreated or treated and uninfected suggests a synergistic toxicity resulting from the combination of infection, handling, and poly ICLC treatment, although other explanations are possible.

Extension of the mean time to death of mice with a lethal infection of Venezuelan equine encephalomyelitis virus by antithymocyte serum treatment.

The mean time to death of mice infected with Venezuelan equine encephalomyelitis (VEE) virus was increased 2 days by antithymocyte serum (ATS) treatment given 1 day before and 1 day after virus inoculation. Virus assays of blood, brain, and spleen indicated that VEE virus replication was delayed by ATS. Additionally, mice treated with ATS exhibited neurological signs later than untreated mice. During the infection, the percentage of splenic B lymphocytes as determined by surface immunoglobulin staining increased. ATS treatment caused a further elevation of the percentage of splenic B lymphocytes. These results show a selective depletion of the non-immunoglobulin-bearing lymphocyte population during VEE virus infection and support the hypothesis that ATS destroys or alters an important population of cells associated with the normal course of pathogenesis and the replication of VEE virus to high titers in the mouse.

Venezuelan equine encephalomyelitis virus infection: effect on monoamine metabolism of mouse brain.

Venezuelan equine encephalomyelitis virus infection: effect on monoamine metabolism of mouse brain.

Host Defenses During Primary Venezuelan Equine Encephalomyelitis Virus Infection in Mice

Abstract The capacity of humoral antibody to confer protection against Venezuelan equine encephalomyelitis (VEE) infection did not require participation of cellular components of the immune response. Likewise, immune spleen cells conferred protection without participation of either preformed antibody or induction of an anamnestic antibody response. Time after donor immunization was a critical factor in determining the antiviral potential of transferred cells, and mice boosted with a second immunization of attenuated VEE virus did not have their antiviral capacity restored. Protection induced by transfer of immune spleen cells was immunospecific but could be inhibited by in vitro treatment of cell preparations with antithymocyte serum or anti-ϑ serum but not by treatment with anti-mouse γ-globulin. There was no evidence that preformed interferon contributed to the protective activity of passively transferred immune cells. Apparently, both humoral antibody and cellular immunity play important roles in protection against VEE virus infection in mice.

Host Defenses During Primary Venezuelan Equine Encephalomyelitis Virus Infection in Mice

Abstract Attenuated Venezuelan equine encephalomyelitis virus immunization produces an antigen-reactive cell population in mice which is capable of responding specifically to homologous viral antigen. This reaction is short lived, involves thymus-derived or dependent (T) lymphocytes and requires the presence of macrophages in the culture system. Antibody competitively blocks T cell recognition and transformation. Booster immunization with attenuated VEE virus 35 days after initial immunization restores lymphocyte reactivity to previous peak values but produces only a bone marrow-derived or dependent lymphocyte response. Passive transfer studies demonstrate that only antigen-reactive cells which are susceptible to being killed by antisera directed at the T lymphocyte are capable of conferring adoptive immunity in a normal recipient.

Experimental Venezuelan equine encephalomyelitis virus infection of the bovine.

Two groups of four dairy cows (Bos taurus) were infected subcutaneously with the epizootic Venezuelan equine encephalomyelitis virus (VEE) strains MF-8 and San Pelayo, respectively. Animals experienced no clinical illness, but all developed significant neutropenia. Virus was recovered once each from the blood of three animals but did not exceed 10(2.2) SMICLD(50) (Suckling mouse intracerebral lethal dose(50))/ml. Specific neutralizing antibodies appeared in the serum of all animals, but there were no significant differences in titers against different naturally occurring VEE subtypes. Dairy cattle thus appear to play no role in virus transmission during VEE epizootics but may serve as retrospective immunological sentinels of virus activity.

Pathogenesis of Venezuelan Equine Encephalomyelitis Virus

Summary The pathogenesis of an attenuated and an unattenuated strain of Venezuelan equine encephalomyelitis virus infection in suckling mice as studied by infectivity titrations and direct fluorescent antibody-staining technique was described. Both strains of VEE virus caused a pantropic infection in suckling mice regardless of the concentration of inoculum used or the route of inoculation given. Viral antigen was detected in many tissues, notably in the central nervous system and in the pancreas. However the intensity of antigenic fluorescence was rather weak, making it difficult to discern sequential development of the viral antigen in infected tissues.