Chronic toxicity and oncogenicity of N-methylpyrrolidone (NMP) in rats and mice by dietary administration.

A two-year feeding study in rats and an 18-month feeding study in mice were conducted to evaluate the potential chronic toxicity and oncogenicity of NMP in Crl:CD (SD)BR rats and B6C3F1/CrlBR mice. Groups of 62 male and female rats were administered diets containing 0, 1600, 5000, or 15,000 ppm of NMP for approximately 2 years. Groups of 50 male and female mice were administered diets containing 0, 600, 1200, or 7200 ppm NMP for approximately 18 months. In vivo parameters were evaluated weekly during the first 3 months of the study, and every other week or monthly during the remainder of the study. For rats, an ophthalmoscopic examination was conducted prior to study start and near the end of the study. Periodically, blood samples were collected from rats and mice for determination of leukocyte differential counts, and from mice for red blood cell morphology. After approximately 2 years of dietary administration in rats and 18 months in mice, all surviving animals were sacrificed. Selected tissues were processed for morphological evaluation. Over the course of the two-year study in rats, test substance-related decrements in body weight and weight gain occurred in 15,000 ppm males and females, which correlated with decreased food consumption and food efficiency. A toxicologically significant, test substance-related increase in the incidence of severe chronic progressive nephropathy occurred in 15,000 ppm males. Several morphological changes noted grossly and/or microscopically were secondary to the increased severity of chronic progressive nephropathy. NMP was not oncogenic in male or female rats at dietary concentrations of 15,000 ppm and below. A test substance-related decrease in the percentage of 15,000 ppm males surviving to the end of the two-year study compared to the control group resulted from the higher incidence of severe chronic progressive nephropathy. However, a sufficient population of 15,000 ppm rats were at risk for potential oncogenicity, so the lower survival did not impair the ability to detect an oncogenic response in this study. There were no adverse, test substance-related effects on the incidences of clinical observations, ophthalmic observations, or differential leukocyte counts in males or females, or on survival of females at any dietary concentration. Male and female mice administered dietary concentrations of 7200 ppm had significantly increased liver weight, significantly increased incidence of hepatocellular adenoma, and significantly increased foci of cellular alteration in the liver. At 7200 ppm, male mice also had an increased incidence of hepatocellular carcinoma while the increased incidence of hepatocellular carcinoma in female mice fell within the historical control range. In addition, the incidence of hepatocellular hypertrophy was increased in 7200 ppm males. Liver weight and hepatocellular hypertrophy were also increased in 1200 ppm males. There were no adverse, test substance-related effects on the incidences of clinical observations, food consumption, body weight, differential leukocyte counts, red blood cell morphology, or survival in either males or females at any dietary concentration. Under the conditions of the study, the no-observed-effect level for NMP was 5000 ppm for male and female rats, 600 ppm for male mice, and 1200 ppm for female mice.

90-day subchronic toxicity study in rats and mice fed N-methylpyrrolidone (NMP) including neurotoxicity evaluation in rats.

In mice, there were no effects on body weight or food consumption. As observed in rats, mice fed 2,500 or 7,500 ppm exhibited a change in urine coloration which was not associated with morphological changes in cholesterol, triglycerides, calcium, and alkaline phosphatase occurred at 28 days but not 90 days. These changes are thus assessed as being of minor toxicological relevance. Liver weights were elevated in males fed 2,500 or 7,500 ppm and centrilobular hypertrophy was seen in both sexes fed 7,500 ppm. These changes may be regarded as an adaptation process but are clearly related to NMP exposure. Other toxicological endpoints examined were unaffected by NMP. The NOAEL was 3,000 ppm for both sexes of rats based on body weight effects and changes in 3 neurobehavioral parameters (males only) at higher feeding levels. In mice, the NOAEL was 1,000 ppm based on liver responses to higher concentrations.

Neural lesions in the rat and their relationship to EEG delta activity following seizures induced by the nerve agent soman.

This study describes the neural structures damaged following exposure to the nerve agent soman, shows there are time-dependent differences in the extent of damage in certain structures, and relates seizure-induced increases in delta band (0-3.5 Hz) electroencephalographic (EEG) activity with severity of subsequent neuropathology. Rats, instrumented to record cortical EEG activity, were pretreated with the oxime HI-6 (125 mg/kg, i.p.) and then challenged with soman (180 ug/kg, s.c.). All animals developed continuous epileptiform seizures that lasted in excess of 4 hr. Groups of animals were perfused 1, 3, 10 or 30 days following exposure. Paraffin-embedded brains were stained with hematoxylin and eosin; thirty-four neural structures were examined and scored for neural damage. All cortical areas sustained damage, with piriform and perirhinal cortices exhibiting the most severe. Subcortical limbic areas (amygdala, amygdala-piriform transition zone, hippocampus, claustrum) and various thalamic nuclei were most consistently and severely damaged in all animals regardless of survival time. Brainstem structures, cerebellum, spinal cord, and other motor output nuclei were never damaged. It was found that some structures were rated as more severely damaged when evaluated at shorter survival times. Severity of neural damage was related to high levels of EEG delta power recorded 24 hr after exposure; power during the acute seizure or 24 hr body weight loss did not predict lesion severity. Sections between AP -0.8 to -4.8 contain cortical and subcortical structures that can be readily and reproducibly evaluated for brain damage.

Further evaluation of the incorporation of an immunotoxicological functional assay for assessing humoral immunity for hazard identification purposes in rats in a standard toxicology study.

A previous study (Ladics et al., 1995) conducted in our laboratory using the known immunosuppressant agent, cyclophosphamide, indicated that a functional assay for assessment of humoral immunity may be conducted in rats in a standard toxicology study. The objective of this study was to further examine the feasibility of conducting an immunotoxicological assay for assessing humoral immunity in rats in a standard toxicology study using a chemical, carbon tetrachloride (CCl4), whose principal target organ of toxicity is not the immune system. Specifically, the previous study and this study were done to determine whether the conduct of an assay for assessing humoral immune function would affect standard toxicological endpoints. Male CD rats were untreated or dosed orally for 30 or 90 days, excluding weekends, with vehicle or 12.5 or 25 mg/kg CCl4. Six days prior to sacrifice, selected rats were injected intravenously with sheep red blood cells (SRBC) for assessment of humoral immune function. One day prior to necropsy, blood for hematological and clinical chemical measurements was collected from each rat. On the day of necropsy standard protocol tissues were collected, weighed, processed to slides, and later examined microscopically. One-half of each spleen was used to assess spleen cell numbers and quantitate lymphocyte subsets (Thelper; Tcyt/sup; total T- and B-cells) by flow cytometry. Serum was analyzed for anti-SRBC IgM antibody by using an enzyme-linked immunosorbent assay. Administration of 12.5 and 25 mg/kg CCl4 for 30 days decreased SRBC-specific serum IgM levels 42 and 45%, respectively, while 25 mg/kg CCl4 for 90 days increased SRBC-specific IgM levels by 50%. CCl4 did not alter splenic lymphocyte subset numbers nor the weight nor morphology of lymphoid organs. Exposure to 25 mg/kg CCl4 did increase liver weight and serum sorbitol dehydrogenase levels, as well as produce centrilobular fatty change. SRBC administration did not alter any hematological or clinical chemistry parameters, nor lymphocyte subset numbers. With the expected exception of the spleen (slight increase in number and size of germinal centers), administration of SRBC did not significantly alter the weights or morphology of routine protocol tissues. Furthermore, administration of SRBC did not mask the rather mild hepatotoxic effects of CCL4 exposure observed in this study. Based on these and previous findings, it appears that a functional assay for assessing humoral immunity may be conducted in animals on standard toxicology study without altering standard toxicological endpoints.

An ongoing validation of a Tier I screening battery for detecting endocrine-active compounds (EACs).

After previously examining an estrogen receptor agonist (17beta-estradiol), several additional compounds have been evaluated in a Tier I screening battery for detecting endocrine-active compounds (EACs): an estrogen receptor antagonist (ICI-182,780, ICI), an androgen receptor antagonist (flutamide, FLUT), a testosterone biosynthesis inhibitor (ketoconazole, KETO), a 5alpha-reductase inhibitor (finasteride, FIN), and an aromatase inhibitor (anastrozole, ANA). The Tier I battery incorporates two short-term in vivo tests (a 5-day ovariectomized female battery and a 15-day intact male battery) and an in vitro yeast transactivation system (YTS). The Tier I battery is designed to identify compounds that have the potential to act as agonists or antagonists to the estrogen, androgen, progesterone, or dopamine receptors, steroid biosynthesis inhibitors (aromatase, 5alpha-reductase, and testosterone biosynthesis), or compounds that alter thyroid function. ICI administration decreased uterine estrogen and progesterone receptor number in the female battery, increased serum follicle-stimulating hormone (FSH) levels and caused spermatid retention in the male battery, and activated gene transcription in the YTS containing the estrogen receptor. FLUT administration increased uterine stromal cell proliferation in the female battery and decreased weights for all androgen-dependent tissues, induced Leydig cell hyperplasia, and caused hormonal alterations (increased testosterone (T), estradiol (E2), dihydrotestosterone (DHT), luteinizing hormone (LH), and FSH) in the male battery, and competed for binding to the androgen receptor in the YTS competition assay. In the male battery KETO decreased weights for all androgen-dependent tissues, caused hormonal alterations (decreased T and DHT and increased LH and FSH), and induced spermatid retention. FIN decreased seminal vesicle and accessory sex gland (ASG) unit weight and caused hormonal alterations (decreased DHT and increased LH, and PRL) in the male battery. KETO was judged not to affect any of the endpoints in the female battery. ANA decreased ASG unit weight and serum E2 levels in the male battery. Using the responses obtained for all the endpoints in the Tier I battery, a distinct "fingerprint" was produced for each type of endocrine activity against which compounds with unknown activity can be compared. These data demonstrate that the described Tier I battery is useful for identifying EACs.

Repeated dose toxicity study (28 days) in rats and mice with N-methylpyrrolidone (NMP).

Twenty-eight day feeding studies were conducted to evaluate the repeated dose toxicity of NMP, a widely used industrial solvent, in Crl:CD BR rats and B6C3F1 mice. Groups of 5 male and 5 female rats each were fed either 0, 2,000, 6,000, 18,000, or 30,000 ppm NMP; similar groups of mice were fed either 0, 500, 2,500, 7,500, or 10,000 ppm. In vivo parameters, hematology and clinical chemistry parameters, and complete pathology evaluations were conducted after approximately 28 days. Decrements in mean body weight gains, reflecting decreases in food consumption and efficiency, were seen in male rats fed 18,000 ppm and in both sexes fed 30,000 ppm. In rats, clinical chemical changes, indicating possible compound-related alterations in lipid, protein, and carbohydrate metabolism, occurred at 18,000 ppm in males and 30,000 ppm in both sexes. No histopathological changes in rats were judged to be directly related to NMP exposure. Hematological (mild to moderate leukopenia) and histopathological alterations (hypocellular bone marrow, testicular degeneration and atrophy, and thymic atrophy) were judged to be secondary to nutritional and body weight effects in male and/or female rats at 30,000 ppm. In mice, cloudy swelling of the epithelia of the distal parts of the renal tubuli was observed in 4 males and 3 females at 10,000 ppm and in 2 male mice at 7,500 ppm. For both rats and mice, abnormal urine coloration was observed (in mice at 2,500 ppm and above, and in rats at 18,000 ppm and above). The discoloration was interpreted as a sign of systemic availability of the test substance, but not as an adverse effect. The NOAEL was 6,000 ppm for male rats and 18,000 ppm for female rats. In mice, the NOAEL was 2,500 ppm based on the kidney histopathology.

Chronic toxicity/oncogenicity of dimethylacetamide in rats and mice following inhalation exposure.

The potential chronic toxicity and oncogenicity of dimethylacetamide (DMAC) was evaluated by exposing male and female rats and mice to 0, 25, 100, or 350 ppm DMAC for 6 hr/day, 5 days/week for 18 months (mice) or 2 years (rats). Clinical pathology was evaluated at 3, 6, 12, 18, and 24 (rats only) months. An interim euthanization for rats occurred at 12 months and hepatic cell proliferation in rats and mice was examined at 2 weeks and 3 and 12 months. No compound-related effects on survival were observed. Rats exposed to 350 ppm had lower body weight and/or body weight gain. There were no compound-related effects on body weight or weight gain in mice at any concentration. There were no compound-related adverse effects on the incidence of clinical signs of toxicity in rats or mice. No hematologic changes were observed in either species. Serum sorbitol dehydrogenase activity was increased in rats exposed to 350 ppm. Serum cholesterol and glucose concentrations were significantly higher in 100 and 350 ppm female rats. Compound-related morphological changes were observed in the liver. In rats, exposure to 100 or 350 ppm produced increased absolute and/or relative liver weights, hepatic focal cystic degeneration, hepatic peliosis, biliary hyperplasia (350 ppm only), and lipofuscin/hemosiderin accumulation in Kupffer cells. In mice, exposure to 100 or 350 ppm produced increased absolute and relative liver weights (350 ppm females only), accumulation lipofuscin/hemosiderin in Kupffer cells, and centrilobular single cell necrosis. Male rats exposed to 350 ppm also had significantly higher absolute and relative kidney weights which correlated with the gross and microscopic changes resulting from a compound-related increase in severity of chronic progressive nephropathy. Female mice exposed to 350 ppm had an increased incidence of bilateral, diffuse retinal atrophy. No increase in hepatic cell proliferation was seen in mice or rats at any exposure concentration. DMAC was not oncogenic under these experimental conditions in either the rat or mouse. The NOAEL for male and female rats and mice is 25 ppm.

Subchronic toxicity study in rats with 1-methyl-3-propylimidazole-2-thione (PTI): effects on the thyroid.

A 90-day gavage study was performed to evaluate the subchronic toxicity of 1-methyl-3-propylimidazole-2-thione (PTI) when administered to Crl:CD BR rats. PTI is a chemical catalyst and is structurally similar to the thioureas, which are known to adversely affect the thyroid. Therefore, this study was designed to investigate the effects of PTI on the thyroid. Male and female rats were dosed with 0, 5, 10, 25, or 75 mgPTI/kg/day for 13 weeks. Clinical pathology examinations and pathology examination were performed and the following were measured periodically: serum T3, T4, and TSH, hepatic UDP-glucuronyltransferase activity, and cell proliferation of the thyroid and liver. Under the conditions of this study, the overall no-observed-adverse-effect level (NOAEL) for the subchronic effects of PTI in male and female rats was 10 mg PTI/kg/day. The NOAEL was based on the effects on the thyroid gland in male and female rats dosed with 25 and 75 mg PTI/kg/day, as well as the hepatic centrilobular fatty change, increased severity of chronic progressive nephropathy, fatty change in the adrenal medulla, and the substantial reduction in body weight and body weight gain. The primary target organs were the thyroid and liver. Alterations in thyroid hormones (T3, T4, and TSH) occurred predominantly at 25 and 75 mg/kg/day. Toxicologically significant alterations in T3, T4, and TSH levels, cell proliferation, and UDP-glucuronyltransferase activity occurred in rats dosed with 25 and 75 mg/kg/day, which correlated with organ weight and histopathological effects. Additionally, the effect of PTI on thyroid peroxidase activity, a key step in thyroid hormone synthesis, was evaluated in vitro using microswine thyroid microsomes. PTI was shown to inhibit thyroid peroxidase, with an IC50 of 0.02 M. These data suggest that PTI enhances the excretion of T4 via induction of glucuronyltransferase and inhibits thyroid hormone synthesis via a direct affect on thyroid peroxidase. Both of these effects contribute to the disruption of the hypothalamic-pituitary-thyroid axis and result in sustained elevation of TSH and the corresponding thyroid hypertrophy and hyperplasia.

Possible incorporation of an immunotoxicological functional assay for assessing humoral immunity for hazard identification purposes in rats on standard toxicology study.

The objective of this study was to examine the feasibility of conducting an immunotoxicological assay for assessing humoral immunity in rats on standard toxicology study. Male CD rats were untreated or dosed intraperitoneally daily for 30 or 90 days, excluding weekends, with vehicle or 2 mg/kg cyclophosphamide (CY). Six days prior to sacrifice, selected rats were injected intravenously with sheep red blood cells (SRBC). One day prior to necropsy, blood samples for hematological and clinical chemical measurements were collected from each rat. On the day of necropsy standard protocol tissues were collected, weighed, processed to slides, and examined microscopically. One-half of each spleen was used to prepare a single cell suspension in order to assess spleen cell numbers. Serum was analyzed for anti-SRBC IgM antibody using an enzyme-linked immunosorbent assay. A second set of studies was performed to examine further the effect of SRBC administration on lymphoid organ weights using 30- and 90-day study age-equivalent naive male CD rats. Exposure of animals to 2 mg/kg CY for 30 or 90 days resulted in a 28% and 61% decrease, respectively, in SRBC-specific serum IgM levels. CY treatment also caused mild alterations in some leukocytic parameters, with significant decreases of 35% and 33% in white blood cell and lymphocyte counts, respectively, observed in 30-day CY-treated animals receiving SRBC. Injection of SRBC alone did not alter hematological or clinical chemistry parameters. With the expected exception of the spleen (increased number and size of germinal centers), administration of SRBC did not significantly alter the weights or morphology of routine protocol tissues. Furthermore, administration of SRBC did not mask the immunosuppressive effects of CY treatment under the conditions of this study. Based on our preliminary findings, a functional assay for assessing humoral immunity may be conducted in animals on standard toxicology study.

Chronic toxicity/oncogenicity of dimethylformamide in rats and mice following inhalation exposure.

The potential chronic toxicity and oncogenicity of dimethyl-formamide (DMF) was evaluated by exposing male and female rats and mice to 0, 25, 100, or 400 ppm DMF for 6 hr/day, 5 days/week for 18 months (mice) or 2 years (rats). Clinical pathology was evaluated at 3, 6, 12, 18, and 24 (rats only) months. An interim euthanasia for rats occurred at 12 months and hepatic cell proliferation in rats and mice was examined at 2 weeks, 3 months, and 12 months. No compound-related effects on clinical observations or survival were observed. Body weights of rats exposed to 100 (males only) and 400 ppm were reduced. Conversely, body weights were increased in 400 ppm mice. No hematologic changes were observed in either species. Serum sorbitol dehydrogenase activity was increased in rats exposed to 100 or 400 ppm. There were no compound-related effects on the estrous cycle of rats or mice at any concentration. Compound-related morphological changes were observed only in the liver. In rats, exposure to 100 and 400 ppm produced increased relative liver weights, centrilobular hepatocellular hypertrophy, lipofuscin/hemosiderin accumulation in Kupffer cells, and centrilobular single cell necrosis (400 ppm only). In mice, increased liver weights (100 ppm males, 400 ppm both sexes), centrilobular hepatocellular hypertrophy, accumulation of lipofuscin/hemosiderin in Kupffer cells, and centrilobular single cell necrosis were observed in all exposure groups. These observations occurred in a dose-response fashion and were minimal at 25 ppm. No increase in hepatic cell proliferation was seen in mice or female rats. Slightly higher proliferation was seen in male rats exposed to 400 ppm at 2 weeks and 3 months but not at 12 months. Dimethylformamide was not oncogenic under these experimental conditions in either the rat or mouse.

Histiocytic sarcoma in an aging gerbil.

A histiocytic sarcoma in an aging female gerbil is described. The neoplasm primarily involved the spleen and liver, and these organs were considered the primary sites of neoplastic origin. No neoplastic infiltration was noted in the uterus or ovaries as is commonly seen in the female mouse. This is the first report of histiocytic sarcoma in gerbils.

Experimental Rift Valley fever in rhesus macaques.

Rift Valley fever (RVF) is a major cause of human morbidity and mortality in endemic areas of sub-Saharan Africa and has the potential to cause epidemic disease in receptive areas world-wide. In this study, a RVF viral isolate from the 1977 Egyptian epidemic (ZH-501) inoculated intravenously into rhesus macaques caused a benign viremic infection in most, but resulted in the hemorrhagic fever syndrome in 20 per cent (3 of 15). Serious disease of this type has not previously been observed in nonhuman primates inoculated with RVF virus and may be a consequence of the viral strain used or the route of inoculation. Severe disease was accompanied by extensive liver necrosis, disseminated intravascular coagulation, and microangiopathic hemolytic anemia. We also attempted to prevent RVF by passive transfer of serum from vaccinated rhesus monkeys (plaque-reduction neutralization test titer 1:2,560). As little as 0.025 ml/kg prevented the development of viremia in naive rhesus monkeys after subcutaneous inoculation of virus. The monkey model should be helpful in understanding the pathogenesis and prevention of human RVF.

The gerbil, Meriones unguiculatus, a model for Rift Valley fever viral encephalitis.

The gerbil, Meriones unguiculatus, was investigated as a model for the encephalitic form of Rift Valley fever. Resistance to necrotizing encephalitis was age-dependent with 100% mortality at 3 weeks, decreasing to approximately 20% by 10 weeks of age in outbred gerbils inoculated subcutaneously. Fatal encephalitis in the 10-week-old adults was dose-independent [1.0-7.0 log10 plaque forming units (PFU), subcutaneously]. Viral replication and histological lesions were followed serially throughout the course of the infection in young (4 week) and adult (10 week) gerbils. Viral replication was evident in the brain tissue of young gerbils from day 4 (3.0 log10 PFU/g) through day 7 (6.0 log10 PFU/g), the last day the young gerbils survived. Virus was only detected in the brain tissue of a single adult gerbil (day 7, 4.0 log10 PFU/g) of 26 studied in the sequential survey. In contrast, two moribund adult gerbils had approximately 7.0 log10 PFU/g of virus in the brain tissue on days 8 and 11. When young and adult gerbils were inoculated with a low dose (50 PFU) of virus intracranially, there were no detectable differences in the course of infection with all animals succumbing to fatal necrotizing encephalitis approximately 7 days postinoculation. The young gerbil becomes the first animal model in which uniformly fatal RVFV-induced encephalitis is produced without significant extraneural lesions.

Pathogenesis of Rift Valley fever virus (RVFV) in inbred rats.

The pathogenesis of Rift Valley fever in adult rats from 3 inbred strains (LEW, MAXX, WF) was investigated. WF rats all died by day 2 postinoculation with viral tissue titers reaching 9 log10 PFU/g. LEW and MAXX rats were resistant to liver disease, but fatal necrotising encephalitis developed in 16 and 44% of the rats, respectively. Detection of serum neutralising antibody on day 3 coincided with clearance of virus from serum and liver, although infectious virus was detected in spleen homogenates as late as day 19 postinfection. Viral titers in LEW and MAXX rats did not exceed 4.5 log10 PFU/g. Cyclophosphamide immunosuppression of LEW rats led to death 5-9 days postinfection; early patterns of viral replication were not affected, but continued growth in the liver resulted in fatal hepatitis. These animals could be protected by passive antibody therapy administered on days 2-5 postinfection to mimic the serum neutralising antibody pattern seen in unmanipulated infected LEW rats. Thus, RVF virus replication and spread is rapid in the WF rats tissues, whereas in LEW and MAXX rats viral growth is less due to an intrinsic mechanism which allows sufficient time for an immune response to terminate infection. A slightly diminished immune response may lead to the development of encephalitis more frequently in MAXX than LEW rats. These rat strains should be useful in elucidating those mechanisms of resistance which limit RVFV-induced hepatitis and encephalitis.

Prophylaxis of Rift Valley fever with antiviral drugs, immune serum, an interferon inducer, and a macrophage activator.

Rift Valley fever virus (RVFV), a member of the family Bunyaviridae, extended its range from sub-Saharan Africa into Egypt in 1977. Its clinical spectrum is recognized to include severe manifestations such as hemorrhagic fever and encephalitis. For these reasons, as well as the limited knowledge of specific therapy for Bunyaviridae infections, we investigated several prophylactic regimens for RVF in a mouse model. Rimantadine, thiosemicarbazone, and inosiplex were ineffective. Pretreatment with glucan was of some use, but the most encouraging results were obtained with the antiviral drug ribavirin, passive antibody, or an interferon inducer polyriboinosinic-polyribocytidylic acid complexed with poly-L-lysine and carboxymethylcellulose (poly[ICLC]). Ribavirin and poly(ICLC) were also shown to be efficacious in preventing disease in hamsters. Ribavirin (loading dose of 50 mg/kg followed by 10 mg/kg at 8-h intervals for 9 days) suppressed viremia in RVF-infected rhesus monkeys. Ribavirin also reduced virus yield in infected cell cultures; sensitivity varied markedly with cell type but not with virus strain. Immune mouse ascitic fluid, with a plaque reduction neutralization titer of 1:1024, was effective in a dose of 4 ml/kg, a volume approximately equivalent to administration of a unit of convalescent plasma to a human. Poly(ICLC) may well have functioned through interferon induction, since RVFV was shown to be sensitive to interferon in cell culture, and since another macrophage activator (glucan) was only marginally effective. These studies suggest that ribavirin, poly(ICLC), and convalescent plasma may have a role in prevention or therapy of human RVF.

Aerosol stability and respiratory infectivity of japanese B encephalitis virus.

Experiments were conducted to examine the aerosol stability and respiratory infectivity of Japanese B encephalitis virus. At 75 degrees F (about 24 degrees C), survival of the virus as aerosol was inversely related to relative humidity. After correction for physical decay, the mean virus half-lives of the virus were 28, 38, and 62 min at relative humiditis of 80, 55, and 30%, respectively. Virus recoveries as aerosol at 4 min aftr dissemination generally exceeded the theoretical limit of 100%, based on the amount disseminated, to suggest that the process of dissemination operated to deagglomerate or release bound virus from the tissue cells in suspension. Swiss-ICR mice and golden Syrian hamsters were highly susceptible to lethal infections after respiratory challenge. Hartley strain guinea pigs and Fisher-Dunning rats, although infected, based on seroconversion observations, survived the infections. Deaths occurred in squirrel monkeys only after exposure to a high aerosol dose of virus (10(6.0) plaque-forming units). Studies of the virus concentration dynamics and histopathological findings in mouse tissues after aerosol challenge supported a hypothesis for direct transport of virus across the foramina of the cribriform plate to the tissues of the central nervous system to produce primary encephalitis.

Evaluation of a formalin-inactivated Rift Valley fever vaccine in sheep.

A formalin-inactivated Rift Valley fever (RVF) vaccine prepared in cell culture for human use was immunogenic in sheep. Vaccine was administered as a single dose of diluted (1:5) or undiluted vaccine with or without an adjuvant. Serum-neutralizing antibodies induced by RVF vaccine persisted for at least 7 months. Seven of 11 vaccinated sheep with prechallenge plaque-reduction neutralization (PRN80) antibody titers of less than or equal to 10 were protected against challenge exposure with 10(6) plaque-forming units of Zagazig 501 strain of RVF virus. Challenge exposure induced abortion in 2 of 2 pregnant sheep. Five sheep with PRN80 titers greater than or equal 1:20 were protected from detectable viremia after challenge exposure. Additionally, 5 of 6 lambs (3 months old) were protected (by maternal antibodies) against challenge exposure. Challenge control sheep developed clinical disease and detectable viremia after exposure. Virus was isolated from saliva of 1 challenge control sheep and virus was transmitted by contact exposure to 1 of 4 seronegative contact-control sheep. Immunization of sheep with formalin-inactivated RVF vaccine induced a priming effect against RVF viral antigens. Challenge exposure with RVF virus resulted in significantly higher neutralizing titers in vaccinated sheep than in nonvaccinated sheep.