Passive Immunity Strategies to Control Rotavirus Diarrhea in Neonatal Calves

Abstract

The passive transfer of maternal immunity provides essential protection in the newborns. It is well known that the neonatal immune system of mammals and birds is fully competent to mount a primary immune response against infection, developing optimal levels of humoral and cell-mediated immunity. However, it is also known that after birth, newborns are exposed to a great variety of antigens for the first time. The initiation of several primary immune responses to those antigens, which in many cases cause mixed infections and complications, would not be quick or strong enough to overwhelm pathogen replication. Therefore, unless adequate maternal immunologic assistance is provided, neonates have an increased probability of dying after infection with common pathogens. Maternal immunologic assistance thus can provide a critical (though temporary) aid to survival for neonates. The evolutionary process developed effective mechanisms for the passive transfer of both systemic and mucosal immunity from the mother to her offspring. Taking advantage of this natural process, vaccination of the dams has become a well-established practice among veterinary practitioners to prevent neonatal diseases. Dam vaccination increases the levels of passive maternal antibodies transferred from the mother via colostrum and milk intake. This strategy of passive systemic immunity had been applied with optimal results, especially for systemic infections. For enteric infections such as rotavirus caused diarrhea, dam vaccination had been the tool selected to reduce the severity of the disease and morbidity rates in cattle and horses. A complementary or alternative strategy to prevent enteric diseases has been the oral administration of colostrum replacers and immune milk supplemented with protective levels of specific antibodies. Different sources of antibodies, i.e., oral administration of hyper immune plasma; fluid or powdered bovine immune colostrum, fluid or powdered chicken egg yolk IgY enriched in rotavirus-specific antibodies, have been explored and represents effective immunotherapies to prevent rotavirus diarrhea. Passive immunity has been documented to often interfere with newborn active immune responses to natural infections and vaccination. In the recent years, the transference of immune cells and other biomolecules with immunomodulatory properties from the mother to their offspring had been described shedding light on the mechanism behind this interference. New adjuvants, antigen delivery systems and rationale vaccines designs to overwhelm or take advantage of the properties of these passive maternal biomolecules and cells transferred to the newborns are under development. This review will address current knowledge regarding the mechanism behind the protective and immunomodulatory effect of passive immunity strategies to prevent rotavirus diarrhea in the veterinary field.