Aerosol exposure to Zaire ebolavirus in three nonhuman primate species: differences in disease course and clinical pathology.

There is little known concerning the disease caused by Zaire ebolavirus (ZEBOV) when inhaled, the likely route of exposure in a biological attack. Cynomolgus macaques, rhesus macaques, and African green monkeys were exposed to aerosolized ZEBOV to determine which species might be the most relevant model of the human disease. A petechial rash was noted on cynomolgus and rhesus macaques after fever onset but not on African green monkeys. Fever duration was shortest in rhesus macaques (62.7 ± 16.3 h) and longest in cynomolgus macaques (82.7 ± 22.3h) and African green monkeys (88.4 ± 16.7h). Virus was first detectable in the blood 3 days after challenge; the level of viremia was comparable among all three species. Hematological changes were noted in all three species, including decreases in lymphocyte and platelet counts. Increased blood coagulation times were most pronounced in African green monkeys. Clinical signs and time to death in all three species were comparable to what has been reported previously for each species after parenteral inoculation with ZEBOV. These data will be useful in selection of an animal model for efficacy studies.

Comparison of 2 antibiotics that inhibit protein synthesis for the treatment of infection with Yersinia pestis delivered by aerosol in a mouse model of pneumonic plague.

INTRODUCTION: Intentional release of Yersinia pestis will likely be propagated by aerosol exposure. We explored the effects of neutropenia on the outcome of doxycycline and gentamicin therapy. METHODS: Female BALB/c mice were exposed to 20 LD(50) of Y. pestis CO92 by aerosol. Treatments were saline (negative control), levofloxacin at 15 mg/kg every 12 h (positive control), doxycycline at 40 mg/kg every 6 h, and gentamicin at 12 mg/kg every 6 h, 24 mg/kg every 12 h, and 48 mg/kg every 24 h in cohorts of normal and neutropenic mice for 5 days. RESULTS: Control mice died. Positive control mice (levofloxacin) had 100% survivorship in both neutropenic and nonneutropenic groups. Doxycycline treatment in the presence of granulocytes yielded 90% survivorship; all neutropenic mice died after the termination of treatment (P<<.001). For gentamicin, survivorship of mice receiving drug every 24, 12, and 6 h was, respectively, 80%, 80%, and 90% for normal mice and 80%, 100%, and 70% for neutropenic mice. No significant differences were seen in the neutropenia versus normal mouse comparison or by schedule. CONCLUSIONS: Doxycycline behaves in vivo as a bacteriostatic drug, requiring an intact immune system for clearance of the infection after aerosol challenge with Y. pestis. Gentamicin is bactericidal, even when given on a daily schedule. Neutropenia did not significantly affect survivorship.

Severe encephalitis in cynomolgus macaques exposed to aerosolized Eastern equine encephalitis virus.

Cynomolgus macaques exposed to an aerosol containing a virulent strain of eastern equine encephalitis (EEE) virus developed neurological signs indicating encephalitis that corresponded with the onset of fever and an elevated heart rate. Viremia was either transient or undetectable even in animals that succumbed to the illness. The onset of illness was dose dependent, but once a febrile response was observed, macaques were moribund within 36 h. Simultaneously, a prominent leukocytosis was seen; 1 day before being moribund, macaques had a white blood cell count >20,000 cells/ microL. The leukocytes were predominantly granulocytes. Increases in serum levels of blood urea nitrogen, sodium, and alkaline phosphatase were also seen. The rapid onset and severity of neurological signs mirror what has been reported for human cases of disease caused by EEE.

Aerosol exposure to western equine encephalitis virus causes fever and encephalitis in cynomolgus macaques.

Cynomolgus macaques were exposed by aerosol to a virulent strain of western equine encephalitis virus (WEEV). Between 4 and 6 days after exposure, macaques had a significantly elevated temperature that lasted for 3-4 days. Clinical signs of encephalitis began as the body temperature decreased, and then they rapidly increased in severity. Cynomolgus macaques with clinical signs of encephalitis had elevated white cell counts in the blood caused mostly by increased numbers of segmented neutrophils and monocytes. Elevated serum glucose levels also correlated with the severity of the clinical signs of encephalitis. Three cynomolgus macaques died; immunohistochemical evidence of viral antigen was present in the brain and central nervous system (CNS). Microscopic analysis also revealed a marked lymphocytic infiltrate in the CNS. Cynomolgus macaques will serve as a useful model of aerosol exposure to WEEV for the evaluation of potential vaccine candidates.

Genetically engineered, live, attenuated vaccines protect nonhuman primates against aerosol challenge with a virulent IE strain of Venezuelan equine encephalitis virus.

Two live, attenuated strains of Venezuelan equine encephalitis virus (VEE), IE1150K and V3526, were administered to macaques to determine if they could elicit protection against an aerosol challenge with virulent VEE virus of the IE variety (VEEV-IE). These viruses were rescued from full-length cDNA clones of 68U201 (VEEV-IE variety) and Trinidad donkey (VEEV-IA/B variety), respectively, and both have a furin cleavage site deletion mutation and a second-site resuscitating mutation. Both vaccines elicited neutralizing antibodies to viruses of the homologous variety but not to viruses of the heterologous variety. Eight weeks after vaccination, the macaques were challenged by aerosol exposure to virulent 68U201. Macaques vaccinated with V3526 were protected as well as macaques inoculated with IE1009, the wild-type infectious clone of 68U201. However, IE1150K failed to significantly protect macaques relative to controls. V3526 has now been shown to protect macaques against both IA/B [Pratt WD, Davis NL, Johnston RE, Smith JF. Genetically engineered, live attenuated vaccines for Venezuelan equine encephalitis: testing in animal models. Vaccine 2003;21(25-26):3854-62] and IE strains of VEE viruses.

Aerosol infection of cynomolgus macaques with enzootic strains of venezuelan equine encephalitis viruses.

Because Venezuelan equine encephalitis viruses (VEEVs) are infectious by aerosol, they are considered to be a biological-weapons threat. Nonhuman-primate models are needed to evaluate the efficacy of candidate vaccines. In the present study, cynomolgus macaques, after aerosol exposure to either VEEV-IE or VEEV-IIIA, developed fever, viremia, and lymphopenia; the severity of the fever response, viremia, and lymphopenia correlated with the inhaled dose of VEEV. Of the 10 macaques in our study, 7 developed clinical signs indicative of encephalitis, including loss of balance and hypothermia. In the macaque, the enzootic strains used are infectious by aerosol and lead to disease, including clinical encephalitis.