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on May 13, 2009

Poultry conference explores many disease aspects

Selected abstracts of presentations at the Western Poultry Disease Conference are summarized.

New approaches to poultry disease control

David A. Halvorson, University of Minnesota

Dr. Halvorson has long been an exponent of controlled marketing as opposed to flock depletion as a means of controlling outbreaks of non-catastrophic disease. His experience with low pathogenic AI in turkeys in Minnesota led to a state policy of quarantining sites until virus excretion had ceased allowing transport of flocks to processing plants for slaughter.

In contrast, recent outbreaks of low pathogenicity H7 infection in turkey flocks have been controlled by depletion and disposal at great expense. The outbreak of H7 low pathogenicity AI in Connecticut in 2003 was controlled by quarantine followed by vaccination (unnecessary) without depletion of flocks.

It is noted that low pathogenicity influenza falls under the control of individual states in contrast to high pathogenicity avian influenza and exotic Newcastle disease which are under the jurisdiction of USDA-APHIS which mandates destruction and disposal. The approach in Minnesota is not generally applicable in other states with high volumes of poultry exports. Generally U.S. trading partners impose a 90 day embargo on all states with a confirmed outbreak of H5 or H7 avian influenza for at least 90 days following complete eradication of infection.

The proposal by Dr. Halvorson to establish a "new disease control program" is not necessary practical. Outbreaks of low pathogenicity AI due to other than H5 and H7 strains which occur in layer and turkey flocks might be subjected to controlled marketing. In contrast in states with significant broiler populations depletion remains the only acceptable alternative.

Reference is made to the attached review of the "FAST" program currently under consideration by USDA-APHIS which will allow egg producers not affected by an exotic disease to transport eggs to market subject to predetermined biosecurity standards, intensive surveillance and daily demonstration of freedom from infection during and disease emergency.

Molecular typing of infectious bronchitis virus

Dr. H. M. Havez, Free University of Berlin

Producers in Europe are experiencing losses due to variant strains of IB as in the U.S.

Researchers at the Free University of Berlin described a sequence of molecular analysis used to characterize IB isolates from flocks in Germany:

  • General diagnosis of IBV infection is confirmed using reverse transcriptase-polymerase chain reaction using a universal primer pair amplifying fragments within the conserved N-protein gene. This step basically determines that the virus is in fact IB. At this stage, a subtype specific RT-PCR analysis is performed to identify possible subtype 4/91 IB which is frequently encountered and responsible for losses in the EU.
  • Aditional molecular typing of IB strains is carried out using restriction enzyme analysis or sequence analysis of the PCR products. This technique allows characterization of viruses by determining the composition of the S1 gene which codes for the specific antigenic protein which is specific to the IB stain.
  • Additional amplification and the use primer pairs and nest of primers are applied to further characterize isolates.
  • Molecular studies similar to those which are conducted by US laboratories have shown that German flocks are infected with 4/91, D1466, V1397 and a new QX-like IB strain. The QX-like IB now predominates in German broiler flocks demonstrating how variants can emerge and become dominant. The value of this work lies in the fact that it is necessary to administer vaccines which are homologous with the specific strain to achieve optimal protection. A number of cases have occurred within the U.S. resulting in deterioration of shell quality requiring administration of other than traditional Mass-Conn and AR strain IB vaccines.

Control of avian pathogenic E. coli in commercial poultry

D. Karunakaran et al, Agtech Products, Division of Danisco

A survey was conducted on broilers, turkeys, and commercial egg flocks to ascertain the presence of avian pathogenic E. coli (APEC) responsible for deleterious effects on performance at subclinical levels of infection. Examination of the E. coli isolates was carried out in a specialist laboratory using a multiplex PCR procedure. PCR product was subjected to random amplified polymorphic DNA (RAPD) analysis to establish the relationship between the isolates. Administration of the direct fed microbial acting as competitive inhibitors of E. coli reduced the levels of APEC in the intestinal tract in laying hens from approximately 105 to 102.

All APECs are characterized by two or more virulence genes. The potential for pathogenicity among E. coli isolates including APEC can be determined rapidly using the multiplex PCR technique.

Cross protection study of a modified live E. coli vaccine against three heterologous APEC serotypes in commercial broiler chickens

K. Cookson et al

Scientists at Fort Dodge Animal Health in conjunction with Iowa State University examined the effect of three APEC strains (O1, O2, O18) on air sac lesion scores and mortality under controlled conditions. High lesion scores ranging from 2.2 to 2.5 were determined with the three isolates which were administered by the intratracheal route. In contrast non-challenged chicks showed a lesion score of 0.4. Challenge with E. coli resulted in mortalities of 5.8% and 13.9% respectively when O2 and O18 E. coli was administered. Vaccination of day-old chicks reduced lesion scores to values ranging from 1.2 to 1.3 and only 10% mortality was demonstrated in the treatment receiving O18 E. coli which is extremely virulent. Further reduction in the pathogenic effect of E. coli occurred when chicks were vaccinated on day-1 and again at day-18 with lesion scores of 0.7 to 1.0 with mortality ranging from1.3% to 5.6%.

Although these studies were performed on broiler chicks, it is evident that a commercially available E. coli vaccine can protect against airsaculitis and mortality under controlled conditions. It would be expected that this vaccine would be protective when administered to pullets reared in either cage or floor systems.

Assessing the financialimpact of diseases of egg producing flocks

S. M. Shane

Based on the fact that E. coli peritonitis is now regarded as the leading cause of mortality and the most pressing problem in commercial egg production in U.S., simulation studies were undertaken to determine the cost effectiveness of vaccination.

Assumptions included the loss from peritonitis of 5% of a flock of 100,000 hens placed, commencing around the 45 week of age. It is recognized that losses can rise to above 20% of a flock either during the post peak period of the first cycle or following molting. Assuming a mortality of 5% due to E. coli over a 4-week period following the 45th week of production the average cumulative egg production from the flock would be reduced by five eggs during the first cycle and seven eggs during the second cycle. The loss of a dozen eggs over the flock would amount to $27,000 over two cycles given a 30¢ per dozen contribution margin.

Loss of 2% of a flock of pullets among 100,000 chicks started would result in a loss of $7,000 given a transfer cost of $3.50. Administering two doses of E. coli spray vaccine would cost $2,000 for a flock of 100,000 hens. The potential benefit to cost ratio of vaccination attains 15:1.

Structured evaluation of the impact of disease, environmental stress and nutritional deficiencies can be used to develop alternative strategies to prevent disease including vaccination, biosecurity or in some cases no action. Factors specific to an operation in addition to industry cost and return, some micro economic factors, influence cost and revenue at different times. Techniques such as gross marginal analysis can be applied to select the optimal course of action.

Protection against variant strains conferred by the recombinant HVT-IBDV vaccine Vaxxitek

F. Perozo

Studies conducted at the Poultry Diagnostic and Research Center at the University of Georgia and Merial Select showed that the genetically engineered HVT vectored IBD vaccine is effective against a challenge strain of IBD.

The vaccine was administered at day old and SPF chicks and broilers were challenged at 18 and 28 days. Under controlled conditions, survival and bursa-to-body weight ratios demonstrated that the vaccine was effective against a E-strain IBD variant challenge strain. This study confirms the effectiveness of the vaccine against classic type 1 mild and highly pathogenic field strains.

This vaccine may be a candidate to replace or supplement the protection provided by combinations of mild and intermediate vaccines administered to pullets during the first three weeks of rearing. Since the vector is a modified HVT virus, vaccinates will be stimulated to produce antibody to the VP2 capsid protein over a prolonged period. Since the recombinant vaccine contains only a subunit of the genome of IBD, evolution of new variants and reversion is not possible.

Report documenting an outbreak of very virulent infectious bursal disease in Northern California pullets

S. T. Stoute

A paper presented by Dr. Simone T. Stoute and colleagues affiliated to the California Animal Health and Food Safety Laboratory System, Turlock, reported on a outbreak of mortality tentatively ascribed to vvIBD infection.

The presentation made at the 2009 Western Poultry Disease Conference documented mortality of 26% and 34% respectively in the index pullet flocks aged 11 and 14 weeks. Based on the post mortem changes which included edematous bursae of Fabricius and muscle hemorrhage followed by microscopic examination, a provisional diagnosis of IBD was made.

In view of the severity of mortality and the appearance of the lesions, isolates were submitted to the Ohio Agriculture Research and Development Center in Wooster, Ohio for examination by Dr. Daral J. Jackwood. The molecular analysis of the virus showed strong similarity with vvIBD strains isolated in Europe, Asia and Africa. This form of infectious bursal disease is exotic to the U.S. but has been recently identified in Central America. The strain is responsible for severe immunosupression and mortality and prevention requires the application of intermediate-plus vaccines. It is noted that the affected flocks had received three doses of intermediate stain vaccine by the spray route consistent with accepted industry practice.

At the present time the outbreak is under active review by the California Department of Agriculture and U.S. Department of Agriculture.

Critical questions which must be answered are:

  • Is the virus in fact homologous with vvIBD stains which are responsible for severe losses in other than North America?
  • What was the origin of the virus since vvIBD is exotic to the U.S.? Emergence of the infection on a small farm presumes introduction from outside the U.S. with obvious implications for biosecurity.

Egg Industry will report on findings as released by responsible authorities.

In vitro Bio-Mos agglutination of salmonella isolates from California poultry farms

N. Reimers et al

Dr. Nancy Reimers of Cutler Associates obtained isolates of salmonella derived from selected cases from the California Animal Health and Food Safety Laboratory System. Isolates were obtained from chick box papers, environmental drag swabs and from pooled intestines of chicks which had died.

A special agglutination test was developed to screen isolates for their susceptibility to agglutination by Bio-Mos, a mannanoligosaccharide feed additive derived from the cell the walls of Saccharomyces cerivisiae. The in vitro assay demonstrated that Bio-Mos agglutinated 70% of the isolates assayed suggesting that if Bio-Mos is present in feed, a high proportion of Salmonella spp. will be agglutinated and excreted thus inhibiting colonization of the intestinal tract and reducing the level of environmental infection. It is estimated that there is a 5% prevalence rate of SE in California flocks.

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