Biomedical subjects

Y M Saif

Publications and source records attributed to Y M Saif.

At least 19 recordsLinked to original sources

PubMed2006

Detection of antibodies against serotypes 1 and 2 infectious bursal disease virus by commercial ELISA kits.

Two distinct serotypes of infectious bursal disease virus (IBDV) are recognized in chicken and turkey flocks in the United States. Serologic testing of chicken flocks for serotype 1 viruses is routinely performed to monitor disease status and vaccination. Earlier studies indicated that enzyme-linked immunosorbent assay (ELISA) test detects antibodies to both serotypes of the virus, while the virus neutralization (VN) test is serotype specific. It is useful to evaluate currently available commercial ELISA kits for their ability to differentiate between antibodies elicited by the two serotypes. Three trials were performed in which chickens were orally inoculated with either a high or a low dose of serotype 1 STC or serotype 2 OH strains of IBDV. Sera collected at 0, 7, 14, and 21 days from these chickens and antisera procured from naturally infected broiler (n=20) and layer (n=30) flocks were tested with five different commercial ELISA kits and by VN. All ELISA kits detected different levels of antibodies elicited against serotype 1 of the virus and moderate and high levels of antibodies against serotype 2 virus. A correlation existed between the ELISA and the VN titers of experimentally infected chickens. All serum samples tested from the commercial layer flocks and 65% of the broiler flocks had antibodies against the OH strain. However, no correlation between the VN titers and ELISA titers was observed for the commercial broilers and layers sera by the majority of the kits. The results indicated that currently available commercial ELISA kits detect antibodies elicited by the two serotypes of IBDV. Hence, the prevalence of serotype 2 antibodies in the flocks should be considered while determining antibody profiles of the flocks against serotype 1 viruses.

Animals↗

PubMed2005

Development of a ssRNA internal control template reagent for a multiplex RT-PCR to detect turkey astroviruses.

Turkey astrovirus (TAstV), a positive sense single-stranded RNA (ssRNA) virus, is an important causative agent of enteritis of poults. The detection and diagnosis of astroviruses have been mainly dependent on electron microscopy (EM). However, EM is not very sensitive. Reverse transcription-polymerase chain reaction (RT-PCR) has high specificity and sensitivity. Thus, monoplex RT-PCR and multiplex RT-PCR for detection of TAstVs were developed in our laboratory. RT-PCR could be adversely affected by many factors, which would result in lowering the sensitivity of the reaction. To minimize this pitfall of RT-PCR, a ssRNA internal control (IC) template reagent containing two sets of primer sequences (SRV and AFCP) specific to the capsid region of TAstV genomes was developed, and applied to the multiplex RT-PCR. Sixty-four fecal specimens from 2-week-old poults with enteritis were tested using the multiplex RT-PCR with the IC serving as a co-amplification template. An overall test inhibition rate of 12.5% was found for the RT-PCR, which can be used to decrease the false-negative rate. The approach to the generation of the IC developed in this study is simple, convenient and productive, and can be used as a universal protocol to generate a ssRNA IC template reagent for RT-PCR.

Animals↗

PubMed2005

Interference between mild and pathogenic strains of infectious bursal disease virus in chickens.

Infectious bursal disease virus is a contagious, immunosuppressive disease of young chickens that is controlled by vaccination. Cross-protection occurs between different strains of the virus as a result of shared neutralizing epitopes. However, interactions between two antigenically similar strains (a mild and a pathogenic) coinfecting the same host have not been investigated. Groups of specific-pathogen-free chickens were inoculated with a mild strain followed by a pathogenic strain at 0, 16, 24, or 48 hr postinoculation (PI) with a mild strain. Virus persistence and the predominant strain of the virus were determined by reverse transcriptase-polymerase chain reaction and restriction fragment length polymorphism analysis, respectively, in bursas at 2, 4, 8, 14, and 21 days PI with the pathogenic strain. Severity of infection was assessed by the bursa/body weight ratios and histopathologic lesion scores. The mild virus interfered with replication of the pathogenic virus. The greatest interference was observed when the pathogenic strain was inoculated 24 hr PI with the mild strain. The interference phenomenon observed might be due to competition for host receptor sites or production of cytokine(s). This interference phenomenon could have practical implications for vaccine usage and protection.

Animals↗

PubMed2005

Development of antigen-capture enzyme-linked immunosorbent assay and RT-PCR for detection of turkey astroviruses.

Turkey astrovirus (TAstV) is an important agent of poult enteritis. The diagnosis of astroviruses has been dependent mainly on electron microscopy (EM) or immune EM (IEM). To develop other simple, rapid, and reliable diagnostic assays, two antigen-capture enzyme-linked immunosorbent assays (AC-ELISAs), polyclonal AC-ELISA and monoclonal AC-ELISA, were developed in this study. Monoplex and multiplex reverse transcription-polymerase chain reactions (RT-PCRs) were also developed using nondegenerate primer sets specific to the capsid region and degenerate primer pairs specific to the polymerase area of two TAstV. EM was included for comparison. Fecal or intestinal contents samples from naturally and experimentally infected poults with enteritis were examined using the developed assays. The polyclonal AC-ELISA had higher sensitivity and wider detection spectrum than the monoclonal AC-ELISA with group-specific monoclonal antibody (MAb), whereas the monoclonal AC-ELISA had very high specificity but lower sensitivity, which was estimated at 0.06 microg of viral proteins. Small round viruses (SRV) that could be astroviruses or other small viruses were detected in 34.4% of the samples examined by EM. The monoplex RT-PCR results amplified with primers SRV-1-3 and SRV-1-5 revealed that the positive rate of astroviruses was 45.3%, which was 10.9% higher than that of EM even if other SRVs were not excluded. Multiplex RT-PCR with SRV-1-3 and SRV-1-5 and AFCP-F1 and AFCP-R1 and the monoplex RT-PCR with degenerate primers verified that the positive rate of astroviruses was 59.4%, which was 25% higher than that of EM. Both RT-PCRs showed good specificity and wider detection spectrum compared with earlier published data.

Animals↗

PubMed2005

Isolation and characterization of H3N2 influenza A virus from turkeys.

Five 34-wk-old turkey breeder layer flocks in separate houses of 2550 birds each in a single farm in Ohio experienced a drop in egg production from late January to early February 2004. Tracheal swabs (n = 60), cloacal swabs (n = 50), and convalescent sera (n = 110) from the flocks were submitted to the laboratory for diagnostics. Virus isolation was attempted in specific-pathogen free embryonating chicken eggs and Vero and MDCK cells. Virus characterization was performed using agar gel immunodiffusion, the hemagglutination test, the hemagglutination inhibition test, the virus neutralization test, reverse transcription-polymerase chain reaction, sequencing, and phylogenetic analysis. A presumptive influenza virus was successfully propagated and isolated on the first passage in MDCK cells, but initially not in Vero cells or specific-pathogen free chicken embryos. After two passages in MDCK cells, it was possible to propagate the isolate in specific-pathogen free chicken embryos. Preliminary sequence analysis of the isolated virus confirmed that it was influenza A virus with almost 100% (235/236) identity with the matrix gene of a swine influenza A virus, A/Swine/Illinois/100084/01 (H1N2). However, it was not possible to subtype the virus using conventional serotyping methods. The results of genetic characterization of the isolated virus showed that it was the H3N2 subtype and was designated as A/Turkey/OH/313053/04 (H3N2). Phylogenetic analysis of the eight gene segments of the virus showed that A/Turkey/OH/313053/04 (H3N2) isolate was most closely related to the triple-reassortant H3N2 swine viruses [A/Swine/WI/14094/99 (H3N2)] that have been circulating among pigs in the United States since 1998, which contains gene segments from avian, swine, and human viruses. The A/Turkey/OH/313053/04 (H3N2) isolated from turkeys in this study was classified as a low pathogenic avian influenza A virus because it only caused a drop in egg production with minor other clinical signs and no mortality.

Animals↗

PubMed2005

Molecular characterization of the capsid gene of two serotypes of turkey astroviruses.

Astrovirus infections mainly cause acute gastroenteritis in children and young animals. Human astroviruses are well characterized antigenically and genetically. However, information on turkey astroviruses is limited. We isolated two astroviruses (TAstV1987 and TAstV2001) from turkeys and classified them as two different serotypes using a virus neutralization test. To elucidate the differences between these two isolates at the molecular level, further genetic characterization and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis were carried out. The sequences of the complete capsid protein gene of these two isolates were obtained by cloning and sequencing. The percentage nucleotide and predicted amino acid identities for these two sequences along with those of 16 other capsid protein gene sequences from human and animal astroviruses retrieved from GenBank were calculated using MegAlign. The results showed that TAstV1987 and TAstV2001 had 73.3% nucleotide and 82.8% amino acid identities, respectively. An unrooted Neighbor-joining phylogenetic tree of these sequences was generated using MEGA 3 software with 1000 bootstrap replicates. The results of evolutionary analysis showed that TAstV1987 was closely related genetically to another virus, designated TAstV-2, whereas TAstV2001 was not as close to TAstV-2 as TAstV1987. The analysis of the capsid proteins of the two viruses by SDS-PAGE revealed that they had different band patterns, indicating that their capsid proteins consisted of different viral proteins. The findings in this study revealed the molecular differences in the capsid protein gene of TAstV1987 and TAstV2001, which may provide the molecular basis of the antigenic differences between these two serotypes of turkey astroviruses.

Amino Acid Sequence↗

PubMed2004

Antigenicity of two turkey astrovirus isolates.

Astroviruses are positive-sense single-stranded RNA viruses. These viruses cause gastroenteritis in humans and in a variety of animal species, including turkey poults. Only human astroviruses are well characterized antigenically. In the current study, two turkey astrovirus isolates, TAstV1987 and TAstV2001, were antigenically compared using cross-neutralization tests in turkey embryos, as well as cross-reactivity of the two isolates by an enzyme-linked immunosorbent assay (ELISA). The antigenic relatedness values (R) were calculated using the Archetti and Horsfall formula. The R value based on the cross-neutralization tests was 0.56%, which indicates that TAstV1987 and TAstV2001 belong to different serotypes; the R value of the two viruses based on ELISA was 70.7%, which suggests these two viruses share common antigen(s).

Animals↗

PubMed2004

Control of infectious bursal disease virus by vaccination.

In summary, the currently used conventional vaccines are used effectively to control the disease. The promise of the new generation of vaccines has not materialized yet. This is partly due to the incomplete understanding of the molecular basis of immunogenicity resulting in an inadequate immune response. It should be emphasized that RNA viruses such as IBDV are prone to change through a variety of mechanisms. This requires vigilance in monitoring field viruses and the natural history of the disease.

Animals↗

PubMed2001

Effect of selection for increased body weight in turkeys on lymphoid organ weights, phagocytosis, and antibody responses to fowl cholera and Newcastle disease-inactivated vaccines.

The influence of selection was studied for increased 16-wk BW in turkeys on in vivo phagocytic activity, antibody responses to vaccines, and weight of the spleen and bursa of Fabricius. A line (F) of turkeys selected long term for increased 16-wk BW and its corresponding randombred control (RBC2) were compared. Phagocytic activity was evaluated by the carbon clearance assay. Antibody responses to inactivated Newcastle disease virus and Pasteurella multocida vaccines were examined by ELISA. Body weight and relative weights of spleen and bursa of Fabricius of the two lines were also compared. The F line had lower phagocytic activity than the RBC2 line (P < 0.05). In addition, the F line had greater BW, relative weight of spleen, and ratio of spleen to bursa of Fabricius weight (P < 0.01) but had a lower relative weight of bursa of Fabricius at 9 wk of age. However, there were no line differences in the antibody responses to Newcastle disease virus or P. multocida vaccines at 1, 2, 3, 4, 5, or 12 wk after vaccination. Based on the present results, it is suggested that long-term selection for increased 16-wk BW might have resulted in changes in the immune system, as indicated by changes in the relative weights of the spleen and bursa of Fabricius and phagocytic activity. The decreased phagocytic activity in the F line may be partially responsible for increased susceptibility to specific diseases in this line.

Animals↗

PubMed2000

Serum immunoglobulin G and M concentrations did not appear to be associated with resistance to Pasteurella multocida in a large-bodied turkey line and a randombred control population.

Serum IgG and IgM concentrations in a randombred control line (RBC2) of turkeys and its subline (F), selected long term for increased 16-wk BW were compared. Six-week-old poults were challenged with virulent Pasteurella multocida (1.2 x 10(7) bacteria per bird of serogroup A and serotype 3,4). Sera were collected prior to challenge, and concentrations of IgG and IgM in turkey sera were quantitatively estimated with a Sandwich ELISA using the cross-reactive polyclonal antibodies specific for the chicken Ig isotypes. The F-line turkeys had a higher serum IgM concentration than turkeys from the RBC2 line. There was no significant line difference in IgG concentration. The F line had higher mortality and a shorter number of days to death following challenge with P. multocida than did the RBC2 line. No significant correlation coefficient was found between immunoglobulin isotype concentration in serum and days to death following challenge with P. multocida. The present results suggested that prechallenge IgG and IgM concentrations in serum did not appear to be associated with resistance to P. multocida in a large-bodied turkey line and a randombred control population.

Animal Husbandry↗

PubMed2000

Flow cytometric analysis of T lymphocyte subpopulations in large-bodied turkey lines and a randombred control population.

To investigate the effect of BW selection on immune cell populations of turkeys, T lymphocyte subpopulation analyses were conducted using peripheral blood from lines selected for increased BW and a randombred control population. The lines used included an experimental line (F) selected long-term for increased 16 wk BW, a randombred control line (RBC2) that served as the base population of the F line, and sire lines (A and B) from each of two major commercial turkey breeders. The peripheral blood lymphocytes were isolated and stained with mouse anti-chicken CD4 and CD8alpha antibodies in flow cytometric analysis. The polymorphism of CD8alpha in the F and A lines detected with the CT8 monoclonal antibody (mouse anti-chicken CD8alpha antibody) did not appear to be associated with BW and shank parameters. The present results showed that the F line had a significantly larger CD4+CD8- T cell subpopulation than did the RBC2 line at both ages, and this population proportion in the F line was also larger than that for one commercial sire line at 24 wk of age. There were no differences in other T cell subsets. The BW selection may have resulted in changes in T lymphocyte subpopulations and, therefore, may have affected disease resistance. The increased susceptibility to infectious diseases in the F line may be associated with the higher CD4+CD8- T cell subpopulation and the CD8alpha polymorphism.

Animal Husbandry↗

PubMed2000

Antibody responses to sheep red blood cell and Brucella abortus antigens in a turkey line selected for increased body weight and its randombred control.

Turkeys from a randombred control line (RBC2) and its subline (F) selected for increased 16-wk BW were tested for primary and secondary antibody responses to SRBC antigen and Brucella abortus antigen (BA). Previous studies have shown that the F line was more susceptible to Pasteurella multocida and Newcastle disease virus than was the RBC2 line. Individuals from the RBC2 and F lines were intravenously injected with 1 mL 5% SRBC antigen or 0.1 mL undiluted BA at 4 and 6 wk of age; blood samples were collected at 0, 4, 7, and 10 d post-immunization. Total, IgG, and IgM titers were measured by agglutination assays. Compared with the RBC2 line, the F line had generally higher total anti-SRBC titers; the differences were significant at 14 d postprimary immunization (PPI) (females); at 10 d postsecondary immunization (PSI) (males); and 4, 7, and 10 d PSI (females) (P < or = 0.05). The F line also had higher IgM titers at 14 d PPI (females) and at 10 d PSI (males) (P < or = 0.05). For IgG titers, a line difference was evident in females at 4 and 10 d PSI (P < or = 0.05); the F line had higher titers than did the RBC2 line. For the antibody response to BA in males, the F line had lower total and IgM titers at 10 d PPI (P < 0.05) than did the RBC2 line. No significant line differences in response to the BA were found in total and IgM titers in female turkeys or in IgG titers in both sexes at any time. These results suggest that selection for fast growth rate of turkeys might have resulted in changes in humoral immunity to the SRBC antigen and BA.

Animals↗

PubMed1999

Variation in resistance to Pasteurella multocida among turkey lines.

Previous research has shown that a line (F) of turkeys selected long-term for increased 16-wk body weight was more susceptible to challenge with washed Pasteurella multocida than a randombred control line (RBC2), the base population of F. A previous study also indicated that the mortality of the F line following challenge with P. multocida was similar to that of sire lines from two of the three major primary breeders. The purpose of the present study was to compare the resistance of the sire line from the third major primary turkey breeder (C) not previously studied with that of the F and RBC2 lines to determine whether there is variation in resistance among the sire lines from three major primary breeders. The sire lines from all three primary breeders were used in the production of commercial turkeys. Body weights of the F line were greater than those of the C line at the time of challenge with P. multocida. Both the C and F lines were heavier than the RBC2 line. The birds were challenged at 6 wk of age with a field isolate of washed P. multocida (1.2 x 10(7) organism per bird of capsular serogroup A and somatic serotype 3,4). Mortality was recorded daily for 14 d. Mortality following challenge with P. multocida was higher in the F line than in the C line, and both large-bodied lines had higher mortality than the RBC2 line. Based on the present results and those published in the literature, there may be variation in resistance among commercial sire lines from the three major primary breeders.

Animal Husbandry↗

PubMed1999

Cross-reactive anti-chicken CD4 and CD8 monoclonal antibodies suggest polymorphism of the turkey CD8alpha molecule.

To measure turkey CD4 and CD8 T cell levels, the cross-reactivity of mouse anti-chicken CD4 and CD8 monoclonal antibodies (mAb) with turkey leucocytes was tested by flow cytometric analysis of blood obtained from individuals in five turkey lines. The turkey lines used included a randombred control population (RBC2), a subline (F) of RBC2 selected for increased 16-wk BW, and a sire line (A, B, and C) from each of three commercial turkey breeders. Peripheral blood lymphocytes were isolated and stained with single or dual color staining. The CT8 mAb (anti-chicken CD8alpha) failed to detect the CD8alpha molecule in some turkeys, and there were large line differences in ability to detect the CD8alpha molecule. However, certain anti-chicken CD8alpha mAb (3-298, 3-292, and 11-39) had good cross-reactivity with the turkey CD8alpha molecule. These present data indicate that the turkey CD8alpha molecule is polymorphic. Some anti-chicken CD4 mAb (CT4, 2-6, 2-35, and 7-125) were also cross-reactive with the turkey CD4 molecule. Immunoprecipitation and Western blotting showed that the 3-298 mAb precipitated a 33- to 35-kDa polypeptide from the turkey splenocyte lysate under reducing conditions. The availability of cross-reactive anti-chicken CD4 and CD8 mAb will facilitate the studies of immune responses in turkeys.

Animals↗

PubMed1999

Effect of selection for increased body weight on mitogenic responses in turkeys.

Mitogenic responses were examined for purified peripheral blood mononuclear cells (PBMC) and whole blood from individuals in a line (F) of turkeys selected for increased 16-wk BW and its corresponding randombred control (RBC2). The PBMC were isolated by centrifugation over Histopaque-1077 density gradient and tested for mitogenic responses to concanavalin A (Con A; 25 microg/mL) and phytohemagglutinin (PHA)-M; 100 microg/mL). For the whole blood assay, 6-wk-old poults from both lines were injected with inactivated Pasteurella multocida. Heparinized blood samples were collected prior to injection (0 d) and at 2, 4, 7, and 14 d postinjection. The diluted whole blood was then tested for the mitogenic responses to Con A (25 microg/mL) and PHA-M (25 microg/mL). The cultures were then pulsed with 3H-thymidine, and incorporation was measured using a liquid scintillation counter. There was a line difference in the mitogenic responses to Con A for PBMC and whole blood assays, but no line difference was observed in the response to PHA-M for both assays. For the purified PBMC assay, the F line had a lower response than its randombred control line (P < or = 0.05) to Con A expressed as either cpm or a stimulation index (SI; ratio of cpm for stimulated cells to the cpm for unstimulated cells). For the whole blood assay, the F line had generally lower SI values in the responses to Con A than the RBC2 line, with differences being significant at 0 and 2 d postinjection (P < or = 0.01) and at 14 d postinjection (P < or = 0.05). Genetic selection for increased BW might have affected the lymphoblastogenic potential of Line F that could affect disease resistance.

Animals↗

PubMed1999

Influence of body weight restriction in a body-weight-selected line of turkeys on response to challenge with Pasteurella multocida.

Previous research has shown that a line (F) of turkeys selected long-term for increased 16-wk BW was more susceptible to challenge with washed Pasteurella multocida (PM) than a randombred control line (RBC2), the base population of the F line. Published research indicated that the mortality of the F line following challenge with PM was similar to that of two commercial sire lines. The purpose of the present study was to determine the influence of reducing BW of the F line to that of the RBC2 line by nutrient restriction on resistance to PM. Four challenge trials were conducted over a 2-yr period. The BW of a group of F line birds was restricted to that of the RBC2 line by limiting access to feed from 1 to 6 wk of age. The F line restricted birds and full-fed RBC2 and F line birds were challenged with a field isolate of washed PM (1.2x10(7) organisms/bird of capsular serogroup A and somatic serotype 3, 4) at 6 wk of age. Birds were checked twice daily for 14 d. Resistance to PM was measured by days to death of those that died and percentage mortality. The BW of the restricted group of the F line did not differ from full-fed RBC2 birds for males or females. In males, the restricted F line birds had similar mortality (48.0%) to the full-fed RBC2 line birds (44.3%), and the mortalities in both groups were significantly lower than that observed for the full-fed F line birds (81.3%) following challenge with PM. The mortality following challenge in females did not differ significantly among groups, even though mortality of the full-fed F line birds (64.1%) and restricted F line birds (63.3%) was more than 9% higher than that (54.2%) observed for the full-fed RBC2 line birds. Days to death was not a sensitive indicator of resistance to PM, as no differences among the three groups of birds were observed for either sex.

Animals↗

PubMed1999

Effect of feed withdrawal or challenge with Pasteurella multocida on growth, blood metabolites, circulating growth hormone, and insulin-like growth factor-I concentrations in eight-week-old turkeys.

The daily effects of feed withdrawal or a bacterial disease (Pasteurella multocida; PM) challenge was studied in a slow-growing line of turkeys. The following groups (n = 6 birds/group) were sampled for up to 13 d: untreated control (CON), 4-d feed withdrawal followed by refeeding (FAST), a group that succumbed within the first 2 to 3 d after PM challenge (E-DEAD), a group that succumbed 8 to 9 d after PM challenge (L-DEAD), a group that survived the PM challenge (SUR), and a group treated with both PM challenge and 4-d feed withdrawal followed by refeeding (FAST/CHAL). Daily feed intake and BW gains were markedly reduced in the E-DEAD and L-DEAD groups immediately and 3 d after PM challenge, respectively. Feed intake and BW gain between CON and SUR groups of turkeys were not different throughout the trial. The turkeys in the FAST group followed the expected feed withdrawal and refeeding patterns for feed intake and BW loss or gain. The FAST/CHAL turkeys consumed the minimal amount of feed to maintain BW after refeeding. Plasma uric acid sharply increased 1 d prior to death in both E-DEAD and L-DEAD groups of turkeys. Plasma uric acid also increased each consecutive day during fasting in the FAST and FAST/CHAL groups of turkeys. Plasma growth hormone was measured in only the CON and FAST groups and increased from about 40 to 85 ng/mL in the FAST group during fasting but returned to control levels within 1 d of refeeding. Circulating plasma insulin-like growth factor-I (IGF-I) decreased from about 17 to 5 ng/mL in the PM-challenged (E-DEAD, L-DEAD, and FAST/CHAL groups) and FAST groups. The concentration of IGF-I returned to prefeed withdrawal levels within 3 d of refeeding the FAST group of turkeys. It was concluded that 1) turkey poults that were not susceptible to the PM challenge generally maintained physiological functions at control bird levels, 2) susceptible turkey poults generally exhibited depressed feed intake and BW gains, and 3) poults challenged with both feed withdrawal and PM treatment responded differently than poults challenged with either feed withdrawal or challenge with PM. The depletion of energy intake and mobilization of energy stores in susceptible poults might have contributed to the rate at which PM caused the poults to die.

Animals↗

PubMed1998

Infectious bursal disease and hemorrhagic enteritis.

Infectious bursal disease (IBD) of chickens and hemorrhagic enteritis (HE) of turkeys are caused by infectious bursal disease virus (IBDV) and hemorrhagic enteritis virus (HEV), respectively. Both diseases have common features, including an acute stage followed by immunosuppression, resulting in lowered resistance to a variety of infectious agents and poor response to commonly used vaccines. The IBDV and HEV infections are widespread in commercial chicken and turkey flocks, respectively. The acute stage of the disease, the immunosuppression that follows, and the widespread distribution of both diseases, are major factors contributing to the economic significance of both diseases. The mechanism of immunosuppression for both infections has similarities, both affect lymphocytes and macrophages, and both are lymphocidal. In this report, an overview of both diseases with emphasis on some of the recent findings will be presented. There has been greater research activity on IBD than on HE, reflecting the relative economic importance of the species affected and the recent changes in the antigenic make up and pathogenicity of the IBDV.

Animals↗