Identification of alpha interferon-induced genes associated with antiviral activity in Daudi cells and characterization of IFIT3 as a novel antiviral gene.

A novel assay was developed for Daudi cells in which the antiviral (AV) and antiproliferative (AP) activities of interferon (IFN) can be measured simultaneously. Using this novel assay, conditions allowing IFN AV protection but no growth inhibition were identified and selected. Daudi cells were treated under these conditions, and gene expression microarray analyses were performed. The results of the analysis identified 25 genes associated with IFN-α AV activity. Upregulation of 23 IFN-induced genes was confirmed by using reverse transcription-PCR. Of 25 gene products, 17 were detected by Western blotting at 24 h. Of the 25 genes, 10 have not been previously linked to AV activity of IFN-α. The most upregulated gene was IFIT3 (for IFN-induced protein with tetratricopeptide repeats 3). The results from antibody neutralizing experiments suggested an association of the identified genes with IFN-α AV activity. This association was strengthened by results from IFIT3-small interfering RNA transfection experiments showing decreased expression of IFIT3 and a reduction in the AV activity induced by IFN-α. Overexpression of IFIT3 resulted in a decrease of virus titer. Transcription of AV genes after the treatment of cells with higher concentrations of IFN having an AP effect on Daudi cells suggested pleiotropic functions of identified gene products.

Inhibition of Dermatophilus congolensis by substances produced by bacteria found on the skin.

Bacteria, isolated from the skins of clinically normal sheep, were tested for inhibitory activity against Dermatophilus congolensis grown in vitro. Out of 85 bacterial isolates, 19, mainly Bacillus spp., showed zones of inhibition when grown together with D. congolensis. The inhibitory activity was shown to be due to the metabolites released by the bacteria.

Lymphocyte proliferative responses and the occurrence of dermatophilosis in cattle naturally infested with Amblyomma variegatum.

The proliferative response of lymphocytes from tick-infested Zebu type, N'Dama and Friesian cattle and acaricide-treated Zebu types and Friesians in concanavalin A (Con A) stimulated cultures was monitored regularly for periods ranging from 11 to 27 months. The numbers of ticks on the animals and the presence of dermatophilosis were also noted. The Friesian cattle carried most and the N'Dama fewest Amblyomma variegatum ticks. The tick-infested Friesians all developed severe clinical dermatophilosis within 5 months of becoming tick-infested. Dermatophilosis lesions on the tick-infested Zebu type and N'Dama cattle were less common and less severe especially in the N'Damas. The proliferative response of lymphocytes from tick-infested Friesians in Con A stimulated cultures fell to almost half that of the acaricide-treated Friesians soon after the former became tick-infested. The tick-infested Zebu types also developed a depressed response compared with the tick-free Zebu group over a 27 month study period. However, the responses of the N'Damas was similar to that of the tick-free Zebu types. The addition of autologous serum to Con A stimulated cultures of lymphocytes derived from the tick-infested Zebu types and N'Damas suppressed their proliferative response compared with that of similar cultures for the tick-free Zebu types.

Sweet itch: responses of clinically normal and affected horses to intradermal challenge with extracts of biting insects.

In a study of the skin reactivity of horses with lesions of sweet itch, six clinically normal horses and seven affected horses were challenged intradermally with extracts of Culicoides, Stomoxys, Tabanidae and Culex species. All the affected horses and three of the normal horses responded strongly to the culicoides extract. The skin reactions in the affected horses reached their maxima within 4 h in the majority of animals. Skin reactivity to culicoides was transferred to normal horses with serum from affected animals confirming that the reaction was an immediate hypersensitivity reaction. Three of the seven affected animals gave both immediate and delayed reactions when challenged with the culicoides extract. When the dermal reactions of 12 clinically normal and 10 affected horses were compared at 20 mins and 1 h after challenge, the reactions produced by the culicoides extract were significantly (P less than 0.025) greater in the affected than in the normal horses. Individual horses gave strong reactions to extracts of Stomoxys, Culex and Tabanidae species, but no consistent response was evident among the affected animals. Serum from horses with sweet itch sensitised the skin of normal horses to challenge with extracts of the biting flies and the transferred antibodies remained bound to the skin of the recipient horse for 72 h or longer. Although some variation among the affected horses occurred in passive transfer experiments, the response to Culicoides species extracts was consistently greater than for the other insect extracts tested.

The anti-bacterial activity of acaricides in relation to streptothricosis.

The anti-bacterial activity of 13 commercially available acaricides, in use in the Caribbean, was tested against Dermatophilus congolensis, an actinomycete involved in streptothricosis of cattle, sheep and goats in the tropics. Acaricides used included organochloride, organophosphorus, carbamate, pyrethroid and amidine compounds. Each acaricide was tested at a typical working dilution used by the farmers, at 25 degrees C and 37 degrees C, in the presence or absence of 15 percent newborn calf serum as a fouling agent. Fouling of acaricides was found to have a marked inhibitory effect on its anti-bacterial activity. Vapona and Cattle Washing Detergent were found to be more active against Dermatophilus congolensis than the other acaricides tested.

Streptothricosis in cattle on the coastal plains of Ghana: a comparison of the disease in animals reared under two different management systems.

The prevalence of streptothricosis in selected cattle herds under two different management systems was investigated and related to the presence of various factors which the literature suggests may play a role in its development. The disease was more prevalent on farms with traditional management compared to that on farms with improved management.

The occurrence of streptothricosis and its association with Amblyomma variegatum ticks in St. Lucia.

Cattle, horses, sheep and goats in all areas of St. Lucia were examined to ascertain the prevalence and distribution of streptothricosis on the island and to investigate its association with the occurrence of Amblyomma variegatum ticks. Although the disease was found to occur throughout St. Lucia it was more prevalent and generally of a more severe form in areas where A. variegatum ticks are present. A tick control programme in the North of the island appeared to have resulted in a dramatic reduction in the prevalence of the disease.

The association between Amblyomma variegatum and dermatophilosis: epidemiology and immunology.

A close association was found between infestation with Amblyomma variegatum and the occurrence of dermatophilosis on cattle on the coastal Plains of Ghana. Animals belonging to breeds traditionally regarded as more susceptible to the disease also tended to carry higher tick burdens. The basis of the association between infestation with this tick and the occurrence of dermatophilosis would appear to involve tick-induced immunosuppression.

Control of Amblyomma variegatum and dermatophilosis on local and exotic breeds of cattle in Ghana.

The occurrence of dermatophilosis on cattle in the tropics is closely associated with infestation by Amblyomma variegatum ticks. Animals that are more susceptible to the disease also tend to carry higher tick burdens. Longitudinal studies carried out on the Accra Plains suggest that N'Dama cattle acquire an enhanced degree of resistance to these ticks following initial exposure. Lesions on zebu-type Ghana Sanga cattle tend to be confined to the predilection feeding sites of adult A. variegatum even when relatively large numbers of ticks are present suggesting that these cattle are able to contain the effects of the tick. Further studies are required to investigate the nature of the apparent resistance of indigenous cattle to the tick and/or its effects and the potential for controlling the disease by immunoprophylaxis using tick derived immunogens. Current methods of controlling the disease depend on the control of ticks using chemical acaricides. Susceptibility to A. variegatum associated dermatophilosis varies between breeds of cattle therefore the level of tick control required is breed dependant. Rigorous tick control is necessary for the prevention of dermatophilosis on highly susceptible exotic breeds of cattle. The limited use of acaricides applied either at the predilection feeding sites of A. variegatum and/or at selected times when the level of challenge increases is sufficient to control the occurrence of the disease on indigenous cattle.

Amblyomma variegatum ticks and the occurrence of bovine streptothricosis in Antigua.

The association between the occurrence of Amblyomma variegatum ticks and streptothricosis was studied on the Caribbean island of Antigua. The prevalence of streptothricosis was higher on animals having A. variegatum ticks compared to that of animals not infested with A. variegatum ticks. There was a steady increase in the prevalence of severe lesions as the level of infestation with adult A. variegatum ticks increased. However the distribution of skin lesions could not be related to the predilection feeding sites of adult A. variegatum ticks.

Effect of insect control on the occurrence and distribution of streptothricosis lesions on cattle.

Trials were set up to ascertain whether the observed occurrence of streptothricosis lesions at dorsal sites on cattle in Antigua was related to the feeding activity of flies. Animals in two herds were treated with insecticide while a third herd served as an untreated control group. There was no significant difference in the occurrence or distribution of lesions on animals in all the three herds over a two month observation period except that a higher proportion of animals in one of the treated herds was affected at the end of the study.

The effect of tick control on the prevalence of dermatophilosis on indigenous cattle in Ghana.

The effectiveness of three tick control regimes on the occurrence of Amblyomma variegatum and dermatophilosis on cattle on the coastal plains of Ghana were compared. Animals at one kraal were sprayed with amitraz at predilection feeding sites of ticks every second week using a high concentration minimum volume technique. Animals at two other kraals were treated with a deltamethrin based pour-on acaricide; at one kraal it was applied once every month while at the other kraal it was used at strategic times based on the expected seasonal increases in the level of infestation with A. variegatum. Animals in a fourth kraal (control group) were treated, by the herdsmen, to control excessive tick build-up as practised under traditional management systems. Fortnightly treatment with amitraz reduced the level of infestation with A. variegatum and the prevalence of dermatophilosis dropped to a low level. The pour-on acaricide similarly depressed the prevalence of dermatophilosis.

Seasonal prevalence of ticks and their association with dermatophilosis in cattle on the Accra plains of Ghana.

The seasonal abundance of adult ticks on cattle and their association with dermatophilosis were investigated in five herds on the coastal plains of Ghana over a 26-month period. Four genera, Amblyomma, Boophilus, Rhipicephalus and Hyalomma were identified, A. variegatum being the predominant species occurring throughout the year with two peaks of infestation, one in April-May and the other in November. A significant positive correlation was revealed between A. variegatum and dermatophilosis in four of the five herds. Significant positive correlations were found between H. m. rufipes and dermatophilosis in two of the herds and between Rh. senegalensis and dermatophilosis in one herd. Negative correlations of statistical significance were observed between Boophilus species and dermatophilosis in three of the herds. Nevertheless, it was considered that A. variegatum was the most important tick factor involved in the pathogenesis of the disease.