The role of the reticuloendothelial system in the immunopathology of Marek's disease.

The role of macrophages in immunity against Marek's disease (MD) was studied. Chickens of one group were subjected to depletion of macrophages using repeated doses of Francil amorphous silica and those of another group were subjected to activation of macrophages using repeated doses of brewer's thioglycollate broth. Chickens of a third group were vaccinated with herpesvirus of turkeys FC 126 vaccine followed by depletion of macrophages. Chickens of these three groups, as well as groups of healthy unvaccinated and healthy vaccinated chickens, were challenged with virulent MD virus. A sixth group of healthy uninfected chickens was kept as a control. The results, based on clinical signs, gross and histopathological studies and agar gel precipitation test (AGPT) for antibodies, indicated that activation of macrophages enhanced immunity against MD and depletion of macrophages had the opposite effect. The protective effect of vaccination against MD was also lowered by depletion of macrophages. The results of AGPT indicated retardation of MD virus replication by macrophage activation and the reverse on depletion.

Suppression of cell-mediated immunity by purified aflatoxin B1 in broiler chicks.

The effect of purified aflatoxin B1 on cell-mediated immunity (CMI) in broiler chicks was assessed using doses of 0.3 and 1 mg/kg feed from hatching to 6 weeks of age. Total lymphocyte and T lymphocyte counts and the 2,4-dinitrofluorobenzene skin sensitivity test, graft-versus-host reaction and nitroblue tetrazolium salt reduction tests were used to evaluate CMI. Both doses of aflatoxin B1, including the apparently nontoxic dose of 0.3 mg/kg feed, caused a significant (P less than 0.05) decline in CMI. The functional activity of splenic macrophages was decreased significantly (P less than 0.05) by both doses of the toxin.

In vivo immunosuppression by synthetic pyrethroid (cypermethrin) pesticide in mice and goats.

Cypermethrin toxicity was produced in mice by intra-peritoneal injection of the pesticide at 50 mg/kg body weight per day for 26 days, and in goats by drenching with cypermethrin at 41.6 mg/kg body weight per day for 30 days. The status of cell-mediated immunity (CMI) was assessed by the 2,4-dinitrofluorobenzene (DNFB) skin sensitivity test. The results indicated significant depression of CMI in the cypermethrin-treated mice and goats. In addition, the humoral immune reaction of the goats intoxicated with cypermethrin was estimated by enumeration of the plaque-forming B-lymphocytes. The rate of plaque formation in the lymphocyte suspension of cypermethrin-treated goats was significantly reduced and the diameter of the plaques was also significantly lower than in that of control animals. The results indicated that cypermethrin suppressed both CMI and the antibody-forming ability of lymphocytes. This immunosuppressive action of cypermethrin is being reported for the first time.

Organ culture of chicken bursa as a model to study the pathogenicity of infectious bursal disease virus isolates.

In vitro study with chicken bursal organ culture was attempted to assess the pathogenicity of locally isolated infectious bursal disease virus (IBDV) initially isolated from the bursa of naturally infected birds. In bursal organ culture, lymphoblastic transformation was noticed as early as 24 hr postinoculation and reached maximum at 72 hr postinoculation. The other microscopic changes were increased number of macrophages and formation of plasma cells. The IBDV antigen was detected 24 hr onward by coagglutination test with antibody coated Staphylococcus aureus strain Cowan I. On the basis of lesion score, the three isolates of IBDV (A, B, and C) were graded as virulent (B isolate) and moderately virulent (A and C isolates). A similar pattern of pathogenicity was also observed in the in vivo pathogenicity studies in chicken based on bursa: body weight ratio and histopathologic lesion score. The bursal organ culture thus provides a useful experimental model to differentiate the IBDV isolates on the basis of their virulence.

Immunosuppression due to chronic ochratoxicosis in broiler chicks.

Crystalline ochratoxin A (OA) was added to the feed of broiler chicks at 0.5 ppm and 2.0 ppm, and humoral and cell-mediated immunity (CMI) were studied. CMI was assessed by skin sensitivity testing, graft versus host (GVH) reaction and T lymphocyte count. Humoral immunity was examined by measuring the haemagglutinin (HA) response to sheep RBC (SRBC). In addition, total lymphocyte counts, total serum protein, albumin and globulin were determined and the phagocytic activity of splenic macrophages was measured in the nitroblue tetrazolium test (NBT). The weights of lymphoid organs were also recorded at post-mortem examination of the birds. Highly significant reductions in CMI were indicated by diminished skin sensitivity, GVH reactions and T lymphocyte counts. On the other hand, only the overall HA titres differed significantly between the various treatment groups. Total lymphocyte counts, total serum protein, serum albumin and serum globulin were significantly depressed on the 21st day of intoxication. The number of NBT-positive cells was drastically reduced in both the intoxicated groups compared with controls (P less than 0.05) and the weights of thymus, bursa of Fabricius and spleen of intoxicated birds were significantly reduced. The study illustrated the immunosuppressive effects of ochratoxicosis in broiler chicks.

The pathology and pathogenesis of Salmonella stanley infection in experimental chicks.

Experimental infection with Salmonella stanley was produced by oral, intravenous and intramuscular routes in day-old chicks. The earliest evidence of the presence of the organisms was in duodenal mucosa six hours after oral infection. Following oral infection the organisms were detected in the duodenum from six hours to five days, in the caecum from 12 hours to nine days, liver, spleen and blood from 24 hours to seven days. The resistance to infection was found to be significant after 10 days old, but not up to six days old. The work confirmed that the survival time of birds given S stanley by the intravenous or intramuscular routes was inversely proportional to the dose up to a maximum beyond which the survival time was not further decreased by dose increase. The presence of S stanley in tissues and blood was detected by isolation and by the fluorescent antibody technique.

Prediction of the occurrence of Marek's disease in chickens on the basis of the quantitation of cell-mediated immunity.

Cell mediated immunity was assayed in chickens on the basis of the dinitrochlorobenzene skin test, T lymphocyte numbers in peripheral blood and the graft-versus-host reaction. It was found that chickens that were to develop clinical Marek's disease following exposure to Marek's disease virus had significantly lower prechallenge levels of cell mediated immunity than those that were resistant to Marek's disease. The graft-versus-host reaction had a smaller coefficient of variation than the other two tests, and it was concluded that this test is likely to be the most reliable indicator of the outcome of infection with Marek's disease virus.

In vivo and in vitro measurement of cell mediated immunity in Marek's disease: role of reticuloendothelial system.

Dinitrofluorobenzene (DNFB) contact-sensitivity test and leucocyte adherence inhibition (LAI) test were performed in this study as in vivo and in vitro tests to measure the cell-mediated immunity (CMI) in chickens subjected to stimulation of reticuloendothelial (RE) system, depletion of RE system and other experimental groups after being challenged with Marek's disease (MD) virus. It was found that CMI was lower in the birds with depleted RE system and infected control birds, whereas CMI was higher in the birds with activated RE system and vaccinated birds as revealed by DNFB contact-sensitivity test. In cases of LAI test, the number of LAI-positive birds were highest in the chicks with depleted RE system particularly in 3rd and 4th month of age, when the incidence of MD was also maximum.

Evaluation of cell-mediated immunity during chronic organophosphate pesticide intoxication in mice and goats.

The status of cell-mediated immunity (CMI) after pesticide exposure was assessed in mice with the help of skin sensitivity and graft versus host reaction tests. It was observed that at 24 hours post-challenge CMI values did not differ significantly from the control, indicating no effect of quinalphos treatment in mice. Goats receiving monocrotophos at a dose rate of 1.0 mg kg-1 body mass for 40 days gave a similar result when CMI was tested with the help of the chemical sensitizer dinitrofluorobenzene (DNFB). Thus the results clearly indicate that the tested organophosphates do not interfere with cellular immunity in the intoxicated animals.

Immunosuppression in broilers under experimental aflatoxicosis.

The effects of purified aflatoxin B1 on cell mediated immunity in broilers were carried out using 0.3 p.p.m. and 1 p.p.m. dose level. The percentage of acid alpha-naphthyl acetate esterase reacting lymphocytes was significantly (P less than 0.05) decreased in chicks fed 0.3 p.p.m. and 1 p.p.m. level of aflatoxin B1. The albumin and globulin values were also significantly decreased (P less than 0.05) at both dose levels.

Use of tetracycline sorbate for the treatment of Aspergillus fumigatus infection in broiler chicks.

The efficacy of tetracycline sorbate (Pimafungil; contains 20% tetracycline sorbate w/v) was evaluated for treatment of Aspergillus fumigatus in naturally infected broiler chicks. The drug was administered to a group of 160 infected broiler chicks at 200 mg/l of drinking water, daily and consecutively for 5 days. Another group of 100 infected broiler chicks was kept as untreated controls. The chicks of the treated group showed appreciable improvement in clinical symptoms, mortality, body weight and recovery as shown by absence of gross and histopathological lesions and of the fungus.

Pathology of Degnala disease in cattle and buffaloes.

Degnala disease, which is believed to be a mycotoxicosis, has clinical syndrome similar to chronic ergotism and is characterised by development of oedema, necrosis and gangrene of the legs, tail, ears, etc. The gross and histopathologic studies revealed thickening of the wall of blood vessels, associated with thrombus formation, and eosinophilic infiltration in the subcutaneous connective tissue of the affected parts of the body.

Fusarium equiseti associated mycotoxins as possible cause of Degnala disease.

In an attempt to find out the etiology of Degnala disease, occurring among buffaloes and zebu cattle in certain rice growing areas of India, preliminary field and laboratory investigations were conducted. On the basis of information so obtained, certain hypotheses (possible causes) were formulated and each of them was examined by instituting laboratory and experimental studies. These investigations suggested the possibility of the involvement of mycotoxins.