Avian pox diseases are contagious and slow spreading viral infections affecting numerous species of birds including chickens and turkeys (Tripathy and Cunningham, 1984). The outbreak of pox diseases in flocks of various species of the birds are quite common in many countries (Biggs, 1982; Garg et al., 1984; Singh et al., 2000) causing major economic losses in terms of mortality, drop in egg production and meat condemnation.

Among various bird species, turkeys are also frequently affected with poxvirus infection in India. The pox disease in turkeys have attracted attention as this disease has been reported in India as well as worldwide, resulted into severe economic losses in spite of proper management and health care (Metz et al.,1985; Beaudette, 1941; Bickford et al., 1971; Dash et al., 2003). This disease causes severe diptheritic and cutaneous lesions leading to high mortality in case of diptheritic form and appreciable economic losses in case of cutaneous form of disease due to meat condemnation. (Tripathy et al. 1997). Pox infection in turkeys tends to be more chronic in nature with longer duration than fowl pox virus (Wakenell, 2001).

The very first time turkey pox virus (TPV) was reported by Brunett in 1934 in a turkey flock in NewYork, Veterinary college. Several outbreaks of turkey pox virus have also been reported in turkey flocks of India (Pandey and Mallick, 1975, Dash et al., 2003).

Pox disease in turkeys is caused by a Ds DNA virus of the family Poxviridae, Subfamily Chordopoxvirinae and Genus Avipoxvirus (Fenner, 1989). Avipoxvirus genus includes fowl pox (FP), turkeypox (TP), quailpox (QP), pigeonpox (PP) and canarypox (CP) as major viral strains. Fowl poxvirus represents the type species of the genus avipoxvirus (Mathews, 1982).

With the perusal of the literature, there is no information available in relation to the characterisation of turkey poxvirus so the present information in this regard will bring about the new avenues for effective management of this economically important disease of turkeys.

Turkey pox is a slow spreading viral disease causing severe economic losses in terms of meat condemnation, weight loss and drop in egg production in Indian turkey flocks. This disease has an emerging status and it was found that the past literature reveals no information with regards to characterization of this virus. Till date, TPV was considered more or less similar to FPV and the available literature reveals the physicochemical characteristics of only FPV and QPV in detail. But now it has been established using cross protection studies that TPV is different from other avipox viruses and this warrants for the characterization of turkey pox virus isolated from natural outbreak of pox in turkeys. Therefore, in this study a turkey poxvirus was isolated from a natural outbreak of pox in turkeys and was characterised using different physico-chemical agents and transmission electron microscope (TEM) technique.

Heat treatment of turkey pox virus was done by subjecting the turkey pox virus isolate to different temperatures (50°C and 60°C) for subsequent periods of time (30 min). The untreated virus showed the titre of 10^7.25 TCID₅₀/ml but when the virus was exposed to 50°C for 30 min the titre was reduced to 10^2.5 TCID₅₀/ml, indicating that the virus is sensitive to this temperature. However, the TPV was completely inactivated at 60°C when exposed for 30 min. The thermostability nature of the turkey pox virus was found to be similar to other avipox viruses like fowl pox virus (FPV) and quail pox virus (QPV) as reported earlier. Mc Culloch (1945) reported that fowl pox virus resisted longer than 1 hr at 50°C. Andrews et al. (1978) reported that inactivation of avian pox virus occurs by heating at 50°C for 30 min or 60 oC for 8 min. Pradhan et al. (1997) found that Quail pox virus could withstand 50°C for 15, 30 and 45 min but the QPV was completely inactivated at 60°C in 8 min.

For the chemical characterization of the turkey pox virus, the virus was treated with ether (20%), chloroform (5%), trypsin (0.25%) and some common disinfectants like phenol (0.5%) and formalin (0.5%). It was found that the infectivity of the enveloped turkey pox virus is sensitive to the effects of lipolytic agent such as chloroform but not with ether. The chloroform treatment (5%) of the turkey pox virus renders the virus to be completely inactivated but with the ether (20%) treatment turkey poxvirus was found stable showing only a decrease in the infectivity titre from 10^7.25 (untreated) to 10^4.75 TCID₅₀/ml. This shows that the virus is somewhat resistant to ether treatment but is chloroform sensitive. Similiarly, Alfalluji et al. (1979) reported that a pox virus isolate from a peacock was ether resistant but chloroform sensitive. Also, Pradhan et al. (1997) found quail pox virus to be more sensitive to chloroform than to ether treatment. Regarding other poxviruses, there are conflicting reports of sensitivity to ether and chloroform treatment. Some authors stated that some pox viruses were sensitive to both ether and chloroform but Tantawi et al. (1979) reported that a pigeon pox virus and its two mutants were resistant to both ether and chloroform. Randall et al. (1964) stated that fowl pox virus is sensitive to both ether and chloroform. Mathews (1982) reported that resistance to ether treatment is listed as one of the taxonomic criterion for pox viruses.

Trypsin in the concentration of 0.25 % at 37°C also inactivated the TPV isolate. Chemicals such as phenol (0.5%) completely inactivated the turkey pox virus whereas formalin (0.5%) reduced its infectivity titre from 10^7.25 (untreated) to 10^3.48 TCID₅₀/ml in the present study. According to Andrews et al. (1978) fowl pox virus can withstand 1% phenol and 1:1000 formalin for 9 days. However Graham and Brandley (1940) reported that 1% suspension of the virus containing 0.25%-0.5% formalin and 0.5% phenol were completely inactivated when stored for 48 hrs at ice box temperature. Pradhan et al. (1997) reported that viability of quail pox virus was not affected by trypsin at a final concentration of 0.25%, But phenol had little effect on infectivity of quail pox virus whereas formalin reduced virus titre by log10^3.38. The effect of different physicochemical agents on turkey poxvirus has been illucidated in the Table-1.

The electron microscopic features of the turkey pox virus was studied by examining the CAM of chicken embryos infected with turkey pox virus as well as scabs collected from turkeys infected with turkey pox virus. The ultra structure and maturation of turkey pox virus was demonstrated by excising the pock lesions from turkey pox virus infected CAM and turkey pox virus infected scabs and studied under TEM after negative staining. The virus showed typical pox virus morphology embedded in CAM sections (Fig. 1.1) and skin samples (Fig. 1.2). The morphology of the TPV was quite clear showing characteristic oval shaped structure with dumble shaped dense core, surrounded by a double layer membrane. The viral particles could be clearly distinguishable and were found free in cytoplasm or in small groups. Some workers like Randall et al. (1964) found that fowl pox virus reveals virus structure as an oval/brick shaped, having average dimensions of 258X354 nm in size. Hyde et al. (1965) had reported that fowl pox virus is a double layered structure which agrees with findings of the present study.

Control on viral diseases is of utmost importance rather than going for treatment after an outbreak has been occurred. The informations on physicochemical characterization of a virus can help in the prevention of the mechanical/horizontal spread of the virus. Therefore, in the present study attempts were made to know the physicochemical characterisation of the turkey poxvirus which may help for its proper management through biosecurity measures. The information generated with examination of turkey pox virus by transmission electron microscopy will help in quick identification of the virus and diagnosis of turkey pox virus of the infected field materials.

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