The microepidemiology of wasting syndrome, a common link to diarrheal disease, cancer, rabies, animal models of AIDS, and HIV-AIDS YHAIDS). The feline leukemia virus and rabies virus models.

Infant cats were inoculated intracranially with rabies or feline leukemia viruses in an experimental study of wasting syndrome. The daily pre- and postinoculation body weights were recorded until kittens were moribund. Affected animals in both groups manifested growth failure or wasting syndrome. Immunodepression, manifested by a conspicuous depletion of thymic cortex, the thymus dependent areas of the spleen, and growth hormone producing-alpha adenopituicytes was significantly (p less than 0.01) related to the wasting status of the animals. The ability of pituitary glands from these animals to produce growth hormone was studied by in situ immunoperoxidase staining and showed a significant (p less than 0.01) difference between healthy and wasted animals. Rabies and feline leukemia viruses were each found responsible for the low immunoreactivity of growth hormone producing alpha adenopituicytes. Because the hypothalamus and the hypophysis were both found infected, it was concluded that regardless of the triggering agent in primary wasting, the hypothalamic-hypophyseal-thymic axis was always involved through a decrease in growth hormone production.

Morphologic appearance of inclusion bodies and their association with the antigenic composition of naturally occurring rabies viruses.

A total of 112 rabies virus-infected skunk brain samples from naturally occurring cases (64 from Missouri, 48 from Kentucky) were code labeled and grouped into two morphologic categories according to the appearance and size of the discrete particles observed by immunofluorescent-antibody staining. The reactivity of the blind-labeled samples was then determined using a panel of 23 antinucleocapsid monoclonal antibodies to test whether morphologic appearance was associated with antigenicity. Two categories were defined and designated; they were morphologic type I (MO-I) and morphologic type II (MO-II). MO-I viruses produced granular-type fluorescing aggregates with no evidence of inclusions compatible in appearance with Negri bodies. MO-II viruses produced at least one and usually many large, round, or oval fluorescing inclusion bodies. No viruses categorized as MO-I reacted with antinucleocapsid monoclonal antibodies 103-7, 239-10, and 120-2; all MO-II viruses reacted positively to these three antibodies, with one exception involving antinucleocapsid monoclonal antibody 239-10. The results indicate a strong association between the reactivity of these antibodies and the morphologic appearance of the aggregates of antigen.

Modern trends in veterinary public health.

The veterinary profession and its contribution to public health should expand in breadth, depth and flexibility to respond to the changing needs of community and society. This longstanding issue is still the subject of controversy between on the one hand those whose scientific activities contribute to our knowledge of food and environmental hygiene, enteric infections, food-borne diseases and zoonoses in general, and on the other the all too numerous traditionalists (even within the profession) who resist the venture of veterinarians into new territories and resent involvement in public health. Veterinarians are ideally suited to function in public health because of their orientation to populations, disease prevention, and the economic implications of disease.

Immunofluorescent examination of the skin of rabies-infected animals as a means of early detection of rabies virus antigen.

Correlations were made on immunofluorescence positivity to antirabies conjugate between cranium-derived nerve fibers in skin and traditional samplings of brain tissue from several species and illness categories of animals with naturally acquired rabies. The overall correlation of results from all categories was about 98% (n, 104) for those that were brain positive and 100% (n, 99) for those that were brain negative. Some animals that ultimately developed rabies were found to have immunofluorescence-positive results 2 or more days before the onset of clinical signs in both natural and experimental infections. The percentage of those with positive skin immunofluorescence results increased as the onset of symptoms approached. From the midcourse period of illness to death, the correlation between skin and brain approached 100%. Different vaccines, commonly given to prevent rabies and other diseases of dogs and cats, were administered to groups of mice and were found to not produce false-positive results when their skin was examined by immunofluorescence for rabies virus antigen. These data suggest that examination of surgical biopsy specimens by immunofluorescence for rabies virus antigen is a useful and reliable diagnostic tool to evaluate the rabies status of biting dogs or cats, or to confirm a clinical diagnosis of rabies in the species tested. The biopsy evaluation of any other species as a means of assessing bite risk is not suggested by these data.

Comparison of primary skunk brain and kidney and raccoon kidney cells with established cell lines for isolation and propagation of street rabies virus.

Cell cultures prepared from skunk kidney, raccoon kidney, and skunk brain were compared with CER, murine neuroblastoma (C1300, clone NA), baby hamster kidney (BHK-21, S-13), and dog kidney (MDCK) cell lines for virus isolation and propagation of street and fixed rabies virus. The skunk brain cells were suitable for efficient replication of all the virus isolates. They were comparable to CER and murine neuroblastoma cells for virus isolation and propagation. None of the other cell cultures was satisfactory. Further work is under way to refine the skunk brain cell cultures.

The dissemination of rabies virus into cranial nerves and other tissues of experimentally infected goats and dogs and naturally infected skunks.

Immunofluorescence examination for rabies virus antigen performed on skin specimens acquired from experimentally inoculated rabid goats and some dogs, often show little or not fluorescence. This observation is contrary to results obtained by comparable examination of the skin of naturally infected animals and most experimentally infected dogs. In an effort to elucidate some factors associated with this experience, an experiment was performed to similarly examine the cranial nerves to see if the limited amounts of fluorescing antigen observed in the skin were also found there. Direct immunofluorescence examination for rabies virus antigen was therefore performed on cranial nerves, face, skin and other tissues excised from experimentally inoculated goats and dogs, and naturally infected skunks. We observed that the cranial nerves of those animals with limited fluorescence in nerves of the skin also contained only limited amounts of rabies virus antigen, while both the cranial and peripheral nerves of naturally infected skunks had large amounts of antigen. All the cranial nerves checked in the experimentally inoculated animals had virus antigen at points close to the brain. Limited fluorescence in the peripheral nerves of rabid animals has been associated with the short incubation period often experienced with experimentally inoculated animals, with the exception of the goat. The incubation period, in turn, is related to the degree of susceptibility of the new host, the quantity of virus, the route of infection, and the degree of adaptation of the virus to the new host.

Detection of La Crosse (California encephalitis) virus antigen in mouse skin samples.

La Crosse (LAC) viral antigen was detected in the skin of inoculated mice. Antigen was detected principally in the dermis of 102 of 120 (85%) mice with clinical signs of illness. To demonstrate the specificity of the fluorescence, LAC virus was isolated from selected samples and was identified by the complement-fixation test. Antigen was most often detected in skin rich in vascular and nerve tissue and was probably disseminated by hematogenous spread. Antigen was found in muscle, vascular, nervous, and other tissues of the dermis, depending on the age of the mice. Antigen was first detected in the skin of 80% of the mice (5 to 6 days of age) on postinoculation day (PID) 3. On PID 4, 100% of these mice were positive, but on PID 5, only 40% were positive, indicating that clearance or neutralization of antigen had occurred in peripheral areas. The skin biopsy technique may be applicable to diagnosis of arboviral infections in other vertebrates.

Post-exposure immunoprophylaxis of goats against rabies.

Uniform groups of young goats, free from rabies antibody, were inoculated with 600,000 mouse LD50 of a dog origin street virus via the massetter muscle. Two vaccine schedules, one consisting of 24 intramuscular doses of ERA vaccine and the other 4 doses of the same vaccine were given to 2 groups of virus inoculated goats and to 2 groups of uninoculated goats respectively. There were no significant differences in incubation periods of the clinically ill goats when the two pos-exposure vaccinated groups were compared. Both treated groups however, had longer incubation periods that the untreated control groups. Essentially the same experiment was done again, this time with 8.0 ml of high titer anti-rabies goat serum administered simultaneously. The incubation periods were prolonged slightly more than in the first experiment. The antiserum alone had the same effect. While no protection from mortality was observed in any group from these post-exposure treatments, it must be recognized that the virus challenge was severe both in dosage and in route of inoculation, and that the use of antibody also had quantitative aspects which were not taken into account. This work should be repeated giving appropriate consideration to the quantitative aspects of both virus and antibody dosage as well as to a less strenuous route of inoculation.

Rabies in a litter of skunks predicted and diagnosed by skin biopsy.

Four juvenile skunks were vaccinated against rabies, descented, and then placed in 4 different households. An illness subsequently developed in 3 of the skunks that was confirmed as rabies, by examination of biopsy specimens of muzzle skin using immunofluorescence microscopy. In 1 clinically normal skunk, the skin was found to be test-positive, predicting that rabies would develop; the signs of rabies became evident in 48 hours. the infection was considered to be field acquired rather than vaccine induced.

Immunofluorescent staining of rabies virus antigen in formalin-fixed tissue after treatment with trypsin.

Formalin-fixed central nervous system tissue from clinically rabid animals was treated with 0.25% trypsin and tested for the presence of rabies virus antigen by direct immunofluorescent (IF) staining. The results were comparable with those obtained from direct IF staining of acetone-fixed standard smears or fresh frozen-cut sections. Experiments were conducted using coded brain specimens (classified as IF-negative, weakly positive, or strongly positive) and showed a specificity of 100% for sections and 92% for smears; the latter figure was subsequently improved by modifying the preparation technique. The specificity of the technique was checked by standard virus neutralization of the conjugate, and by known antibody neutralization of the virus antigen in the specimens. The optimal duration for the trypsin digestion was found to be a minimum of 60 minutes at 37 degrees C or 120 minutes at 4 degrees C. The tissues could be held in buffered formalin for between 3 days and 7 weeks with no apparent difference in the results. Satisfactory concentrations of formalin were 0.125% or 0.25%. Trypsin was found to have no effect on non-formalinized tissues, with the exception that softening occurred making tissues harder to cut and process.The results suggest that trypsinization of formalin-fixed tissue is a valid procedure for the preparation of tissues for IF examination, which would be useful in cases where the current standard techniques cannot be used. However, further evaluation of the method is still required.

Influence of chlortetracycline feeding on salmonellosis in calves. I. Rate and duration of shedding. II. Severity of illness.

Studies were conducted to test the influence of the feeding of chlortetracycline (CTC) on the fecal shedding of S. typhimurium subsequent to experimentally induced infection in calves. Levels of 0, 20, 50, and 100 gm CTC per ton of feed were fed to groups of calves for a two-week period before inoculation and the resulting level of shedding of S. typhimurium quantified. At the 50 gm/ton level, the feeding of CTC was associated with a significantly higher level of shedding than in non-CTC fed controls, and the duration of shedding was longer. Calves fed at 50 and 100 gm CTC/ton were affected much more severely by the inoculation than calves receiving no CTC. The same was true to a lesser extent in the calves fed 20 gm/ton. Observations made on each calf included changes in body temperature, time of onset, severity and duration of diarrhea, straining, and anorexia. Since the fecal output of salmonellae is increased at the level of 50 gm/ton, the authors conclude that this commonly used level of CTC feeding in calves contributes to the size of the salmonella reservoir in nature, thus increasing the risk of exposure to both man and animals alike and otherwise complicates the problems of salmonellosis.