The present study was conducted to investigate the effect of  Spirulina platensis and Chlorella vulgaris   separately and a mixture of both on reduction of viral infection in poultry. In two farms in Monofia Gavernrate where chicks were infected with avain influenza virus (H5N1) . The infected chicks lossed ability of having feed and drink in the two farms also affect the quality and quantity of eggs (eggs not normal in size ,have bad quality , egg shells was very fragile and cracked ) this was in the second farm  . The experiment started by adding 1ml/L from a mixture of Spirulina platensis and Chlorella vulgaris  (50:50) in  the drinking water dially for one week .At the end of the experiment the performance of the infected chicks flock was improved at the first day of application of treatment and all over the treatment course, where the mortality rate was  sharply , the feed and water consumption were increased and the vitality of the chickens was also increased . Also ,the boiler chicks in the second farm started laying eggs with a good quality and quantity . In the laboratory an experiment was done to investigate the effect of Spirulina platensis  extract on 200 one day old Cubb broiler infected chicks (obtained from El-Ahram Poultry Company) . Chicks were fed on commercial ration. The boiler chicks were divided into 4 groups 50 chicks each in a separate battery. Feed and water are available  ad libitum. First group has Spirulina platensis extract and vaccinated with Egy Flu vaccine at 14 day old .Second group has vaccination only ,third group has  Spirulina platensis extract only. Fourth group neither having treatment with Spirulina platensis extractnor vaccinated with Egy Flu vaccine (at 14 day old).All the chicks were vaccinated gainst broiler viral diseases using IB Primer,clone vaccine (against ND),Inactivated vaccine against Newcastle disease (HIPRAVIAR-BPL2) and Gumboro 228 E strain .All groups Challenge by inoculating each chicken via intra nasal rout with 0.1 ml of the  Highly Pathogenic Avian Influenza (HPAI) H5N1) virus containing 106  EID50. The first group of broiler chicks that received Spirulina extract (3 times per week )and vaccination with (Egy Flu vaccine)  were significantly higher  immune response (haemagglutination inhibition) (HI antibody titer ) against Egy Flu vaccine than the second group that received Egy Flu vaccine only. Both G1 and G2 showed significantly higher HI antibody titer than G3 and G4 .
Also, the results revealed that the treated boiler chicks with Spirulina extract and vaccinated with S/C at 14 day old with Egy Flu vaccine chicks ( all over 10 days post challenge with HPAI H5N1 virus) gave high resistance to Avian Influenza (HPAI) H5N1) virus and became as normal in having feed and drinking water and their was one dead chicken only during the period of the experiment .The broiler chicks that neither treated with Spirulina extract nor vaccinated with Egy Flu vaccine were unable to be feed but they have to drink water only and the number of dead chicks increased day by day during the period of the experiment .