Observations on the replication of ectromelia virus in mouse-derived cell lines: implications for epidemiology of mousepox.

Ectromelia virus was shown to replicate in vitro in all lymphoma cell lines and in a small proportion of hybridoma lines tested. It was demonstrated that certain hybridoma cell lines, which were passed in ectromelia virus-infected mice, yielded ectromelia virus infectivity on explantation into tissue culture. This finding further substantiated the belief that ascitic fluid and hybridoma cell lines exposed to virus during mouse-passage could be important in the epidemiology of mousepox.

Reexamination of the efficacy of vaccination against mousepox.

Experiments were conducted to evaluate the efficacy of three strains of vaccinia virus, IHD-T, Lister and Wyeth, to immunize the BALB/cByJ mouse against infection with ectromelia virus. Mice vaccinated with any of the strains were protected for at least 12 weeks against clinically apparent disease when challenged with cage-mates infected with a virulent stain (NIH-79) of ectromelia virus. However, 4 to 8 weeks after vaccination mice were capable of transmitting virus to non-vaccinated cage-mates. The results are discussed within the context of the current practices for preventing and controlling ectromelia epizootics.

Genetic determinants of resistance to ectromelia (mousepox) virus-induced mortality.

Resistance to ectromelia (mousepox) virus-induced mortality was examined in crosses between susceptible DBA/2J, A/J, and BALB/cByJ mice and resistant C57BL/6J and AKR/J mice. Depending on the cross, resistance to mousepox virus was shown to be determined by one or more independently assorting autosomal loci with dominant alleles for resistance in AKR/J and C57BL/6J mice and recessive alleles in A/J, BALB/cByJ, and DBA/2J mice. A sexual dimorphism in resistance to disease was also observed.

Kinetics of ectromelia virus (mousepox) transmission and clinical response in C57BL/6j, BALB/cByj and AKR/J inbred mice.

Research was undertaken to answer basic questions on susceptibility, clinical response and transmission of ectromelia virus in selected strains of inbred mice. C57BL/6J and AKR/J were found to be markedly more resistant to a virulent strain of ectromelia virus (isolated during the 1979-80 outbreak at the National Institutes of Health) than C57LJ, BALB/cByJ, DBA/2J, A.By/SNJ and C3H/HeJ when infected by footpad inoculation. In C57BL/6J and AKR/J the LD50 was about 7 logs higher than the ID50. With one exception, C57LJ, the LD50 and ID50 titers in the other strains were about equal. In C57LJ the LD50 titer was intermediate. Following intragastric inoculation, virus was isolated from feces of C57BL/6J mice for as long as 46 days and up to 29 days from BALB/cByJ mice. Transmission to cage mates from intragastrically infected C57BL/6J and BALB/cByJ occurred up to 36 and 30 days respectively after infection. Virus was isolated from the spleen in 2 of 5 BALB/cByJ mice and 1 of 7 C57BL/6J mice tested 95 days after gastric inoculation. Following footpad inoculation, BALB/cByJ mice consistently transmitted virus to cage mates before death at 10-12 days. C57BL/6J mice transmitted between days 8 and 17, but not beyond. Virus was maintained in C57BL/6J mice by exposure to infected cage mates for seven passages, which was the most attempted. Clinical signs in infected C57BL/6J mice were usually subtle or inapparent.

Evaluation of an enzyme-linked immunosorbent assay for the detection of ectromelia (mousepox) antibody.

Ectromelia virus, an orthopoxvirus that can cause extensive morbidity and mortality (mousepox) in colonized mice, has been epizootically responsible for serious disruption of biomedical research since 1930. The lack of a sensitive and specific serological assay for infection with this virus became apparent during outbreaks of mousepox at the National Institutes of Health, Bethesda, Md., and other biomedical research institutions in 1979 and 1980. To fill this need, we evaluated an enzyme-linked immunosorbent assay. Sucrose gradient-purified ectromelia and vaccinia viruses were compared as antigens in tests on approximately 1,000 mouse sera from experimentally infected mice and conventional colonies of uninfected mice. A statistical analysis based on the frequency distribution of the absorbance values for 152 mouse sera (free of ectromelia antibody) gave 0.22 as a value to differentiate ectromelia-positive sera from ectromelia-negative sera. When enzyme-linked immunosorbent assay results were compared with those obtained by an indirect immunofluorescence assay, the former was found to be at least 10-fold more sensitive. With the procedures employed, including the use of purified vaccinia virions as antigen, the enzyme-linked immunosorbent assay proved to be highly sensitive and specific for detecting antibodies to ectromelia and vaccinia viruses. False-positive results were not encountered. False-negative results were observed in 3% of 108 separate tests of a known positive serum. Although data indicated that ectromelia antibody can be differentiated from vaccinia antibody with homologous and heterologous antigen, this procedure probably cannot be generally used because of unavailability of ectromelia antigens.

Mouse pox threat.

A News and Comment Briefing ("OSHA backs away from strict lab rules," 28 Nov. 1980, p. 992) incorrectly quoted a National Research Council report on safe handling of laboratory chemicals as saying, "For most laboratory environments, ... regular monitoring of the airborne concentrations of a variety of different toxic materials is both unjustified and unjust." The report actually said it was "unjustified and impractical."

Clinical manifestations of eosinophilic memingitis due to Angiostrongylus cantonensis.

Between 1959 and 1976, 34 patients were seen in Hawaii with eosinophilic meningitis. Angiostrongylus cantonensis was recovered from two of these patients. The remaining cases were presumed to be due to this parasite because of clinical and epidemiologic findings. The most likely source of infection for eight patients was ingesting raw terrestrial snails or slugs, and for six patients eating raw or poorly cooked crustaceans. Patients typically presented with severe headache; neck stiffness and fever were usually mild or absent. Paresthesias were noted by most adults. The cerebrospinal fluid (CSF) cell count ranged from 150 to 1500 leukocytes per cubic millimeter, with a mean eosinophil percentage of 38. CSF IgE levels were not abnormal in four patients so studied. Although two deaths occurred, the illness was typically self-limited, resolving completely with no specific treatment.

Transplacental transmission and neonatal infection with swine influenza virus (Hsw1N1) in swine.

To study the question of chronicity or latency of swine influenza virus (Hsw1N1) infections in swine, newborn pigs were exposed to the virus in two experiments, and pregnant gilts were exposed in another experiment. Of five pigs exposed at 5 days of age, virus was isolated from throat swab samples of all (up to 10 postexposure days (PED) in one pig) and from a blood sample from one pig on PED 1 and 3. Virus was not isolated from urine, tissues, or explants of organs from pigs euthanatized PED 20 to 67, and disease was not evident. Of 11 pigs exposed within 2 hours of birth (before consuming colostrum), virus was shed for longer periods (for 10 and 11 days in four pigs) and severe respiratory tract pathologic changes developed. However, there was no evidence of chronic or latent infections. There was evidence of transplacental transmission of virus in one of ten pigs born to pregnant gilts that were exposed 10, 24, and 39 days before parturition, respectively.

Natural history of influenza in swine in Hawaii: swine influenza virus (Hsw1N1) in herds not infected with lungworms.

To obtain more information on mechanisms by which influenza virus is perpetuated in swine, retrospective and prospective seroepizootiologic observations were made in swine herds in Hawaii, beginning in 1974. An epizootic of swine influenza (Hsw1N1) virus was observed in November and December 1976, involving 31 of 41 herds. Features of the epizootic included (1) infection of all herds within one geographic location, during a short period; (2) no obvious introduction of virus from the outside in most herds; (3) epizootics mainly in herds with serologic history of infection; (4) no evidence that lungworms were involved; and (5) little clinical disease associated with infection. There was evidence of viral activity in some herds before the epizootic period and afterward in two of three herds monitored. Evidence of viral transmission by feral animals was not obtained. Data indicated that swine influenza virus persists through latently or chronically infected swine, with epizootics occurring when herd immunity reaches a critically low degree.

Natural history of influenza in swine in Hawaii: prevalence of infection with A/Hong Kong/68 (H3N2) subtype virus and its variants, 1974-1977.

From September 1974 to January 1978, about 25% of 254 swine farms, studied on four of six Hawaiian islands, had swine with antibody to A/Hong Kong/68 (H3N2) subtype of influenza virus. Of 290 swine 2 to 5 years of age in a single herd, 72% had antibody. Antibody titers were consistently higher to A/England/42/72 and A/Port Chalmers/1/73 antigens than to A/Victoria/3/75 or A/Hong Kong/1/68 antigen. Few swine had antibody to the A/Hong Kong/68 antigen. Antibodies to H3N2 and Hsw1N1 subtype of virus persisted at high titer in the same animals for more than 3 years; however, titers to the Hsw1N1 subtype were considerably higher. The occurrence of H3N2 infection in swine appeared shortly after the occurrence of the same H3N2 variant in human population. To date there is no evidence that the H3N2 subtype has become established in swine in Hawaii.

The prevalence of toxoplasmosis on Pacific Islands, and the influence of ethnic group.

The prevalence of Toxoplasma dye-test antibody was determined in inhabitants of a number of Pacific islands, in Melanesia, Micronesia and Polynesia, and on Taiwan. With the exception of one island in French Polynesia, two Hawaiian islands, and Taiwan, Toxoplasma antibody prevalences were high, ranging between 84% and 100% in the adult populations tested. On the Hawaiian islands of Oahu and Hawaii, populated by several ethnic groups, and where about 50% of the total adult populations were estimated to have been infected with Toxoplasma gondii, a marked variation in prevalence of infection by ethnic group was observed. The lowest prevalence in the Hawaiian islands estimated at about 15% to 20% in adults, was observed in Japanese. On Taiwan, only 6% of adult ethnic Chinese and 1% of aborigines tested had Toxoplasma antibody.

Observations on a feline coccidium with some characteristics of Toxoplasma and Sarcocystis.

Two morphologically different cysts were found in skeletal muscles of mice inoculated with fecal material from a stray cat containing Isopora-type oocysts. The most common cyst contained bradyzoites resembling those of Toxoplasma and resulted from an oocyst measuring 11 times 13 mum which appeared to be identical to that of Toxoplasma. The other cyst, observed in only a few mice, contained bradyzoites resembling those of Sarcocystis, but the oocyst or sporocyst that gave rise to it was overlooked and apparently lost. Two more strains of the parasite resembling Toxoplasma were found in feces of stray cats. When inoculated into mice, the oocyst of this parasite routinely produced chronic infection and formed cysts similar to Toxoplasma in skeletal muscles and occasionally in the central nervous system. The majority of infected mice developed Toxoplasma antibody, but only to low titers. Cats fed carcasses of infected mice remained healthy and shed nonsporulated oocysts following a prepatent period of about 5 days. Cats did not develop Toxoplasma antibody. There was little or no cross immunity between the parasite and T. gondii in cats or mice. Transmission of the parasite between mice by the cyst stage normally was not possible; however, mice inoculated with cortisone acetate did become infected when inoculated with cysts. In other laboratory animals inoculated orally with the oocyst asymptomatic infection was detected in 3 species of rats, in guinea pigs and in dogs, but not in monkeys, pigeons or Japanese qualis. Fluorescent antibody tests on human sera failed to provide evidence of natural human infection with the parasite.

Besnoitia species (Protozoa, Sporozoa, Toxoplasmatidae): recognition of cyclic transmission by cats.

Isosporan oocysts, measuring 13 by 16 micrometers, from a cat in Hawaii produced Besnoitia cysts in tissues of mice and rats. Feeding these cysts to cats led to oocyst shedding after 11 to 13 days, continuing for a mean of 11 days. This indicates a two-host cycle for Besnoitia, adding an intestinal phase and oocyst production by a carnivore to the already known tissue stages. Thus a representative of Besnoitia, similar to other species in cattle, horses, reindeer, impala, other mammals, and reptiles, has been shown to be a coccidian of cats, capable of being spread by fecal contamination. Besnoitia is the fourth mammalian tissue parasite, together with Toxoplasma, Hammondia, and Sarcocystis, found to produce isosporan-type oocysts.