We consider a novel approach for developing a stable operational platform for the rapid production of large quantities of therapeutic and preventive countermeasures. This approach involves recruiting the biochemical machinery in shrimp for the production of a vaccine or antibody by infection, using the Taura Syndrome Virus (TSV) carrying a passenger gene for the desired countermeasure. We develop a hybrid model of the shrimp biomass/countermeasure production system, which has two components: biomass production and production of countermeasure (antibody/vaccine). Shrimp have size-dependent characteristics and responses to the external environment. We consider a model based on the classic McKendrick-von-Foerster/Sinko-Streifer size-structured population equations with mass (size) as the structure variable. Moreover, experimental results suggest that the mortality rate in acutely infected shrimp as well as the residency times in the latent phase depend on the length of time that individual shrimp remain acute or latent, respectively. We record the variable residency times in the different stages by introducing a new variable, the class-age of an individual, which in a given stage represents the length of time that the individual spends in that stage. Combining size and class-age we make a first attempt at a size and class-age structured mathematical model to study the progression of TSV infection in shrimp.