Economically Important Non-oncogenic Immunosuppressive Viral Diseases of Chicken—Current Status

Abstract

Immunosuppressive viral diseases threaten the poultry industry by causing heavy mortality and economic loss of production, often as a result of the chickens' increased susceptibility to secondary infections and sub-optimal response to vaccinations. This paper aimed to present an up-to-date review of three specific economically important non-oncogenic immunosuppressive viral diseases of chickens, viz. chicken infectious anaemia (CIA), infectious bursal disease (IBD) and hydropericardium syndrome (HPS), with emphasis on their immunosuppressive effects. CIA and IBD causes immunosuppression in chickens and the socio-economic significance of these diseases is considerable worldwide. CIA occurs following transovarian transmission of chicken anaemia virus and has potential for inducing immunosuppression alone or in combination with other infectious agents, and is characterized by generalized lymphoid atrophy, increased mortality and severe anemia. The virus replicates in erythroid and lymphoid progenitor cells, causing inapparent, sub-clinical infections that lead to depletion of these cells with consequent immunosuppressive effects. The IBD virus replicates extensively in IgM(+) cells of the bursa and chickens may die during the acute phase of the disease, although IBD virus-induced mortality is highly variable and depends, among other factors, upon the virulence of the virus strain. The sub-clinical form is more common than clinical IBD because of regular vaccination on breeding farms. Infection at an early age significantly compromises the humoral and local immune responses of chickens because of the direct effect of B cells or their precursors. HPS is a recently emerged immunosuppressive disease of 3-6-weeked broilers, characterized by sudden onset, high mortality, typical hydropericardium and enlarged mottled and friable livers, with intranuclear inclusion bodies in the hepatocytes. The agent, fowl adenovirus-4, causes immunosuppression by damaging lymphoid tissues; the presence of IBD and CIA viruses may predispose for HPS or HPS may predispose for other viral infections. Synergism with CIA or other virus infections or prior immunosuppression is necessary to produce IBH-HPS in chickens and the susceptibility of chickens infected with fowl adenovirus varies throughout the course of CIA infection. The mechanism of immunosuppression has been studied in detail for certain chicken viruses at molecular levels, which will provides new opportunities to control these diseases by vaccination.

Experimental Coinfection of Chicken Anemia Virus and Mycoplasma gallisepticum Vaccine Strains in Broiler Chicks

“…Immunosuppressive diseases usually negatively affect chickens of the poultry industry by increasing the susceptibility to opportunistic infections by viruses and bacteria (Lutticken, 1997;Balamurugan & Kataria, 2006). Among the known immunosuppressive agents, CAV stands out for its worldwide occurrence, not only in commercial poultry, but also in SPF chickens (Schat, 2003;Balamurugan & Kataria, 2006), backyard chickens (Barrios et al, 2009), as well as contaminates poultry vaccines (Barrios et al, 2012). CAV presents tropism for T-lymphocytes, rendering the cellular immune response ineffective, especially in young chickens, by destroying CD8+ T cells (Adair et al, 1993;Adair, 2000;Brentano, 2009), disabling the protection against intracellular agents.…”

“…It was previously reported that the MG F-strain vaccine may cause disease in the upper respiratory tract of chickens, which is possibly exacerbated when a concomitant secondary infection is present (Lin & Kleven, 1982;Yoshida et al, 2000). Natural coinfections may occur in the field, under appropriate conditions, with vaccine strains, as well as with wild and more virulent strains, potentially causing more significant productivity losses (Balamurugan & Kataria, 2006;Javed et al, 2005). Vaccines against CAV in breeders and MG in layers are commercially available in Brazil and the impact of the respective diseases may be reduced through vaccination.…”

In vitro rapid clearance of infectious bursal disease virus in peripheral blood mononuclear cells of chicken lines divergent for antibody response might be related to the enhanced expression of proinflammatory cytokines

“…Direct losses of poultry are linked to specific mortality because of recent 're-emergence' of the IBDV in the form of antigenic variants and hypervirulent strains. The indirect economic impact of the disease is also considerable, due to virus-induced immunosuppression and/or potential interactions between IBDV and other viruses, bacteria or parasites (Balamurugan and Kataria, 2006). These indirect losses are due to secondary infections, growth retardation and poor immune response to vaccines (Kibenge et al, 1988).…”

Naturally Occurring Co-infection of Avian Leukosis Virus (subgroups A-E) and Reticuloendotheliosis Virus in Green Peafowls (Pavo muticus)

“…Immunosuppressive diseases usually negatively affect chickens in the poultry industry by increasing their susceptibility to opportunistic infections by viruses and bacteria (Balamurugan & Kataria, 2006). Immunosuppression in chickens can be induced by many viruses, including MDV, ALV, REV and CAV (chicken anemia virus), which cause similar lesions, making their diagnosis in the field more difficult .…”