Marek's Vaccine Research Articles

Outbreak and management of Marek's disease in 16 weeks old pullets in Nigeria: a case report

Marek's disease (MD) remains a major concern to chicken farmers, especially because of its adverse effect on birds' growth, livability, and egg production. Veterinarians often consider the prognosis poor, especially when tumors are seen in organs like the liver, spleen, and lungs. This is a report of an outbreak of acute MD in commercial chickens. In the present study, carcasses of 16 weeks old Isa brown pullets were presented at the Veterinary Teaching Hospital, the University of Jos for investigation. They had been vaccinated at the hatchery against Marek's disease at day old. The disease was diagnosed as Marek's disease based on mortality pattern, necropsy findings, histological observations, and polymerase chain reaction analysis. Secondary bacterial infection was caused by Staphylococcus aureus, susceptible to gentamicin. The affected flock was revaccinated using Izovac® HVT Marek's vaccine. As a follow-up, a gentamicin-doxycycline-based oral preparation: Doxygen®, was administered for five consecutive days at 100g/200 litres of drinking water. A significant reduction in mortality was observed within two weeks of the commencement of treatment. Owing to the slow spreading/killing nature of Marek's disease (unlike Gumboro disease), its early detection and management via revaccination and treating secondary bacterial infection can significantly reduce losses.

In ovo administration of Bacillus subtilis serotypes effect hatchability, 21-day performance, and intestinal microflora

Recent research has tried to maximize broiler chick health and performance by utilizing commercial in-feed probiotics to inoculate fertile hatching eggs, and thus expose birds earlier to beneficial bacteria. However, the in ovo inoculation of a specific serotype of Bacillus subtilis was detrimental for broiler hatchability. Therefore, the objective of this study was to determine if other B. subtilis serotypes negatively affect hatchability or if it is associated with a specific serotype. It was also of interest to determine if the B. subtilis serotype influence chick performance and intestinal microflora. On d18 of incubation, 1886 fertile broiler eggs were in ovo inoculated with the following treatments (T): T1 = Marek's vaccine (MV), T2 = MV + B. subtilis (ATCC 6051), T3 = MV + B. subtilis (ATCC 8473), and T4 = MV + B. subtilis (ATCC 9466). It should be noted that in a previous study, T2 was detrimental to hatchability. Inoculated eggs were transferred to 3 hatchers/T. At hatch, chicks were weighed, feather sexed, and hatch residue analysis was conducted. Male chicks were randomly assigned to 40 raised wire cage so that there were 10 birds/cage. On d 0, 7, 14, and 21 of the grow-out, chicks and feed were weighed to calculate performance data. On these days, the ileum and ceca were aseptically collected to enumerate total aerobes and coliforms. No differences were observed for percentage of mid dead embryos, cracked eggs, and cull chicks (P > 0.05). However, hatch of transfer was significantly reduced by T2 compared to T1, T3, and T4 (P < 0.001). T2 had significantly higher percentages of late dead embryos and pips when compared to the other treatments (P = 0.002 and P < 0.001, respectively). Chicks hatched from T2 were not vigorous and, thus, not used for the grow-out trial. No differences were observed for growth performance characteristics for any of the treatments (P > 0.05). For bacterial enumeration, the ileum had equal or fewer bacterial counts for T3 and T4 when compared to T1 on most sampling days, except on d21 where T4 had higher aerobic and coliform counts (P ≤ 0.0001). For the ceca, T3 and T4 had equal or fewer bacterial counts than T1 on every sampling day (P ≤ 0.0001). These data demonstrate that not all B. subtilis evaluated are detrimental to hatchability, but rather, serotype dependent. In addition, different B. subtilis serotypes can modify the intestinal microflora with potential to reduce pathogenic bacteria present in young broiler, without impacting overall performance.

Effects of in ovo probiotic administration on the incidence of avian pathogenic Escherichia coli in broilers and an evaluation on its virulence and antimicrobial resistance properties

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in poultry, which has been traditionally controlled by the prophylactic in-feed supplementation of antibiotics. However, antibiotics are being removed from poultry diets owing to the emergence of multidrug-resistant (MDR) bacteria. Therefore, alternatives to control APEC are required. This study aimed to evaluate the effects of in ovo inoculation of probiotics on the incidence of APEC in broilers and evaluate the virulence and antimicrobial resistance properties of the APEC isolates. On embryonic day 18, 4 in ovo treatments (T) were applied: T1 (Marek's vaccine [MV]), T2 (MV and Lactobacillus animalis), T3 (MV and Lactobacillus reuteri), and T4 (MV and Lactobacillus rhamnosus). A total of 180 male broilers per treatment were randomly placed in 10 pens. The heart, liver, spleen, and yolk sac were collected on day 0, 14, 28, and 42. Presumptive E. coli isolates were confirmed by real-time PCR. The positive isolates were screened for the APEC-related genes (iroN, ompT, hlyF, iss, and iutA), and E. coli isolates containing one or more of these genes were identified as APEC-like strains. A total of 144 APEC-like isolates were isolated from 548 organ samples. No differences (P > 0.05) among treatments were observed for the incidence of APEC-like strains in all organs when averaged over sampling days. However, when averaged over treatments, the incidence in the heart, liver, and yolk sac was different among sampling days; a significant increase was observed in these organs on day 14 compared with day 0. Twenty-five antimicrobial resistance genes were evaluated for all APEC-like isolates, and 92.4% of the isolates carried at least one antimicrobial resistance gene. Thirty-seven isolates were then selected for antimicrobial susceptibility testing; MDR strains accounted for 37.8% of the isolates. In conclusion, the in ovo inoculation of a single probiotic strain did not confer protection against APEC strains in broilers. The high prevalence of MDR isolates indicates that further research on antibiotic alternatives is required to prevent APEC infections in broilers.

In ovo inoculation of an Enterococcus faecium–based product to enhance broiler hatchability, live performance, and intestinal morphology

Previous studies have suggested the use of probiotics, as alternative to antibiotics, to enhance broiler performance. The administration of probiotics in feed has been widely explored; however, few studies have evaluated the in ovo inoculation of probiotics. Therefore, the objective was to evaluate the impact of in ovo inoculation of different concentrations of GalliPro Hatch (GH), an Enterococcus faecium–based probiotic, on hatchability, live performance, and gastrointestinal parameters. Ross x Ross 708 fertile eggs were incubated, and on day 18, injected with the following treatments: 1) 50 μL of Marek's vaccine (MV), 2) MV and 1.4 × 105 cfu GH/50 μL, 3) MV and 1.4 × 106 cfu GH/50 μL, 4) MV and 1.4 × 107 cfu GH/50 μL. On the day of hatch, chicks were weighed, feather sexed, and hatch residue was analyzed. Male birds (640) were randomly assigned to 40 floor pens. On day 0, 7, 14, and 21 of the grow-out phase, performance data were collected. One bird from each pen was used to obtain yolk weight and intestinal segment weight and length. Hatchability was not impacted by any GH treatment (P = 0.58). On day 0, yolk weight was lower for all treatments than for MV alone. On day 0 to 7, feed intake was lower for 105 and 107 GH; the feed conversion ratio (FCR) was lower for all treatments than for MV alone (P = 0.05; P = 0.01, respectively). From day 14 to 21, the 107 GH treatment had higher BW gain (P = 0.05). For day 0 to 21, 107 GH had a lower FCR than MV alone (P = 0.03). On day 0, all GH treatments resulted in heavier tissues and longer jejunum, ileum, and ceca lengths than MV alone (P < 0.05). Spleen weight was higher for 105 and 107 GH than for MV alone. In conclusion, GH does not impact hatchability, and some concentrations improved live performance through the first 21 d of the grow-out phase. These improvements could result from the increased yolk absorption and improved intestinal and spleen morphology seen in this study.

Off-label use of ceftiofur in one-day chicks triggers a short-term increase of ESBL-producing E. coli in the gut.

This trial was designed to evaluate the off-label use of ceftiofur with Marek’s vaccine in one-day-old broiler chicks, a prophylactic treatment that has been done in some commercial hatcheries, on the emergence of extended-spectrum beta-lactamase producing Escherichia coli (ESBL-E. coli). A total of 168 chicks (Cobb500®) were used in a completely randomized design. Birds were assigned to two treatments (Marek’s vaccine plus saline vs Marek’s vaccine plus ceftiofur) and six repetitions, with 14 animals each. Cloacal swabs were collected from 1 to 14 days post-hatch. The majority (86%; p<0.0001) of the ESBL-producing isolates harboring blaCTX-M and blaSHV genes originated from animals receiving the antimicrobial. None of the isolates were positive for plasmid-mediated AmpC betalactamase genes (blaACC, blaCMY-2, blaDHA, blaFOX, blaMOX and blaMIR). These findings indicate that the off-label use of ceftiofur with Marek’s vaccine is associated with the short-term increase in ESBL-producing Escherichia coli in the gut of chicks.

Effect of Marek's vaccine on some lymphoid organs in layers

Effect of Marek's vaccine on some lymphoid organs in layers

Serial Transfer of a Transplantable Tumor: Implications for Marek's Vaccine Mechanisms

The mechanism of Marek's disease (MD) vaccination to prevent the lymphoproliferative disease in chickens is not well understood. It is generally recognized that vaccination prevents disease, including the induction of T-cell tumors, but it does not prevent the pathogenic virus from infecting and replicating in the vaccinated host, nor does it prevent bird to bird spread of the oncogenic virus. The stage at which the vaccinated immune system intervenes in the process from infection to the induction of tumors remains obscure. Using a transplantable tumor induced by the Md5 strain of MD virus (MDV), we show that CVI988 vaccination does not prevent the induction of transplantable tumors in the 15I(5) x 7(1) chicken line. A monoclonal tumor with a V beta 1 T-cell receptor spectratype of 207 base pairs was used to follow the transplantable tumor in serial passages in vivo. This transplantable tumor could be passed in vaccinated birds. The length of time between vaccination and challenge (5 to 12 days) had little or no influence on the ability to transfer the tumor. There was variability in the manifestation of the disease produced by the transplanted tumor. Some chickens presented as normal but were still capable of transmitting the transplanted tumor to newly vaccinated recipients via their blood. This indicates that some chickens can control, but not eliminate, the tumor. The variables inducing health or disease in the challenged chickens remain obscure, but environmental or other factors likely depress the immune system allowing the tumor to overwhelm the immune system.

Serial Transfer of a Transplantable Tumor: Implications for Marek's Vaccine Mechanisms

Serial Transfer of a Transplantable Tumor: Implications for Marek's Vaccine Mechanisms

Loss of Cell-Associated Marek's Disease Vaccine Titer during Thawing, Reconstitution, and Use

Tests of the effects of mismanagement practices observed in hatcheries showed that very subtle deviations from the explicit directions accompanying Marek's vaccine can cause dramatic losses of vaccine potency. Such mismanagement was found to result in 14 to 97% loss of vaccine titer. It appears that procedures used in hatcheries for the handling of cell-associated Marek's vaccine should be closely monitored on a continuous basis to prevent a gradual drift from correct handling.

The Addition of Fowlpox and Pigeon Pox Vaccine to Marek's Vaccine for Broilers

Laboratory and field studies indicated that a cell-culture fowlpox vaccine was effective and safe when administered subcutaneously to day-old broiler chicks in combination with cell-associated Marek's vaccine without compromising the latter. Pox vaccines of chick embryo origin evaluated similarly provided excellent protection, although they caused local musculature swelling when injected into muscle rather than under the skin. No muscle swelling followed improper vaccination with the cell-culture fowlpox vaccine.

Investigation of an Increase of Solid Tumors in Chickens Vaccinated against Marek's Disease

SUMMARY In study of a reported increase in solid tumors (fibrosarcomas, hemangioendotheliomas, and nephroblastomas) in 9-week-old chickens vaccinated against Marek's disease, an increase in solid tumors was confirmed, though probably not a result of any oncogenic activity of the vaccine. A more likely explanation, though purely speculative, seems to be physical transmission of avian leukosis virus among newly hatched chickens during the vaccination procedure. The chickens in this particular commercial operation were found to have a high incidence of infection with avian leukosis virus. The studies confirmed the effectiveness of Marek's vaccine in reducing the incidence of Marek's disease.