Journal of American Science, 2011; 7 (9) http://www.americanscience.org 66 The Relation between some Immunosuppressive Agents and Widespread Nature of Highly Pathogenic Avian Influenza (HPAI) Post Vaccination A. M. Hegazy 1 , F. M. Abdallah 2 , L. K. Abd-El Samie 3 , and A. A. Nazim 4 1 Avian & Rabbit Med. Dept., Faculty of Vet. Med., Zagazig Univ. Zagazig, Egypt. 2 Virology Dept., Faculty of Vet. Med., Zagazig Univ. Zagazig, Egypt. 3 Avian & Rabbit Dis., Vet. Hospital, Faculty of Vet. Med., Zagazig Univ. Zagazig, Egypt. 4 M. V. Sc., Faculty of Vet. Med., Zagazig Univ. Zagazig, Egypt. *a_hegazy52@yahoo.com Abstract: The effect of chicken infectious anemia virus (CIAV) and mycotoxins on immune response of chicken after vaccination against highly pathogenic avian influenza was evaluated. Sixteen chicken flocks (4 broiler flocks ranged between 4 - 6w old and 12 layer flocks ranged between 12 - 57w old) vaccinated against HPAI once in case of broiler flocks and three times in case of layer flocks showed non protective titer by HI and ELISA tests, were tested for the presence of Anti-CIAV antibody using commercially available ELISA kit and the flock's rations were examined for the presence of aflatoxin and ochratoxin using HPLC. All tested flocks were seropositive against CIAV in both broiler flocks (with percentage of 70% & ELISA titers ranging from 2105 to 3728) and layer flocks (with percentage of 71.67% & ELISA titers ranging from 2007 to 3194) of different ages, breeds, and localities in Sharkia province, Egypt. HPLC analysis revealed the presence of aflatoxin & ochratoxin residues in rations despite using antimycotoxin feed additives. The study revealed that CIAV infection and mycotoxicosis might be the cause of vaccination failure against AIV and so the repeated occurrence of AIV infection even in the vaccinated flocks in Sharkia province, Egypt. [A. M. Hegazy, F. M. Abdallah, L. K. Abd-El Samie and A. A. Nazim, The Relation between some Immunosuppressive Agents and Widespread Nature of Highly Pathogenic Avian Influenza (HPAI) Post Vaccination. Journal of American Science 2011;7(9):66-72] (ISSN: 1545-1003). http://www.americanscience.org . Key words: HPAI, CIAV, HI, ELISA, mycotoxins, GMT. 1. Introduction: Highly pathogenic avian influenza (HPAI) was recognized as a global problem, especially in certain Africa countries (Cattoli et al., 2009). World authorities concern that an HPAI H5N1 strain would mutate causing pandemic outbreak in humans. To decrease and prevent that possibility, a vaccination program was enforced nationwide as well as depopulation of affected poultry farms had been conducted in infected areas at the beginning of HPAI outbreaks in Africa in early 2006 as recommended by the Office International des Epizooties. However, such program could not successfully eradicate HPAI from the African countries and so HPAI cases occurred repeatedly in some vaccinated flocks, perhaps because of cultural and economic reasons in the implementation of such program. Although vaccination induced satisfactory antibody reaction to H5N1 experimentally, some vaccinated flocks demonstrated poor, or no, antibody response, especially after one vaccination in young flocks (Jiang et al., 2005). Chicken infectious anemia virus (CIAV) was first isolated in 1979 in Japan (Yuasa et al., 1979). Since then, an increasing interest was paid to that virus, as it was found to have a great economic impact on poultry industry. The virus was incriminated in a disease of young chickens, characterized by a transient severe destruction of erythrocytic and granulocytic series of the bone marrow cells, resulting in aplastic anemia. It also caused severe depletion of lymphocytes from primary and secondary lymphoid organs, resulting in immunosuppression (Yuasa et al., 1979; Taniguchi et al., 1982 & 1983), giving reason for more severe secondary infections and inadequate response to vaccines (Novak et al., 2001; Shuhong et al., 2009). CIAV was proved to participate other immunosuppressive viruses such as infectious bursal disease virus (IBDV) (Yuasa et al., 1980), Marek’s disease virus (MDV) and reticuloendotheliosis virus (REV) (Bülow et al., 1986). It also enhanced the pathogenicity of a wide range of co-infecting pathogens such as Newcastle disease virus (De Boer et al., 1994), Marek’s disease virus (Miles et al., 2001), Adenovirus (Toro et al., 2000), Reovirus (McNeilly et al., 1995). Immunity acquired through vaccination is also impaired by mycotoxins ingestion. The important mycotoxins in poultry rations were aflatoxin and ochratoxin (Girish and Smith, 2008). Mycotoxin- induced immunosuppression may be manifested as depressed T- or B-lymphocyte activity, suppressed antibody production and impaired macrophage/neutrophil-effector functions (Hatori et al., 1991; Mohiuddin, 1992). Suppressed immune function by mycotoxins might eventually decrease resistance to infectious diseases, reactivate chronic infections and/or decrease vaccines efficacy (Oswald et al., 2005). Therefore, the presence of mycotoxins in poultry rations might lead to a breakdown in vaccinal immunity and to the occurrence of diseases