Pullorum Disease, Poultry, and the NPIP
Darrell W. Trampel, D.V.M., PhD.
Iowa State University
December 2, 2013

          Development of purebred chickens can be traced back to 1875 when the American Poultry Association (APA) published a book entitled “Standards of Perfection” which promoted purebred breeds of chickens.  Unlike randomly mated chickens, purebred chickens produced offspring that closely resembled the parent birds and had predictable physical appearance and egg production.  This predictability made purebred flocks more profitable than outbred flocks.  However, in 1916, the International Baby Chick Association (IBCA) was formed as a trade association of hatchery operators following a philosophical disagreement with the APA.   APA members wanted to breed chickens for their form and color and selected breeding birds based upon judging at shows.  Hatchery operators wanted to breed chickens to produce more eggs and selected breeders on the basis of performance testing.  The IBCA sponsored egg-laying contests.

The poultry industry began to grow in the early 20^th century, but a disease known as Bacillary White Diarrhea limited the early expansion of the industry.  This disease, later called Pullorum Disease (PD), was rampant in poultry and could cause upwards of 80% mortality in recently hatched chicks.  Some chicks died before hatching and others died a week or two after hatching with white urates on top of watery droppings.    Poultry producers were unable to cope with this disease until the cause was identified and methods of detection and prevention were developed.  In 1899, the bacteria that caused bacillary white diarrhea, now called Salmonella Pullorum, was discovered.  Ten years later, it was learned that this bacteria could be transmitted from one generation of chickens to the next through contaminated eggs – a novel concept at the time.  By 1913, a blood test was developed that made it possible to test breeder flocks and eliminate reactors so pullorum disease could eventually be eradicated from a flock.  When testing began in 1914, 9.8% of chickens tested were reactors and investigators learned that more than a single test of a flock was necessary to detect and remove all infected individuals.

The potential for rapid, nationwide spread of PD increased dramatically with the emergence of mail-order hatcheries and large, forced-air incubators.  In 1918, the U.S. Postal Service first accepted baby chicks to be shipped by parcel post.  Poultry breeders who developed chickens with superior production capabilities were besieged with orders for baby poultry from all over the country.  The first large electric incubator was developed by Petersime in 1923.  Large incubators provided air movement and uniform temperatures and facilitated expansion of the poultry industry.  These large incubators frequently contained hatching eggs from multiple breeder flocks at the same time.  S. Pullorum from contaminated eggs produced by positive breeder hens was found to be transmitted during the hatching process to clean chicks sharing the same hatching tray.  PD disease was probably introduced into commercial turkey flocks by co-mingling chicken eggs and turkey eggs in forced-draft incubators.  This finding stimulated research to improve hatchery sanitation.

Ensuring that chicken breeding stocks were free of PD was a major motivation for development of the National Poultry Improvement Plan (NPIP).  Groundwork for development of the NPIP was laid at the 1933 IBCA Convention in Grand Rapids, Michigan.  Members agreed upon standard terminology for the breeding and hatching industries to describe different degrees of freedom from PD.  They also adopted a Code of Fair Trade Practices and, because of unethical practices by some members, asked the federal government for help in regulating their industry.  On July 1, 1935, the NPIP became operational after being established by an act of Congress.  Provisions were based upon recommendations from the IBCA.  The NPIP immediately began inspecting hatcheries for S. Pullorum and contaminated hatcheries were shut down.  In addition, the NPIP operated the U. S. Record of Performance program which publically listed how different breeds performed in egg-laying contests.  Use of the stained-antigen, rapid, whole-blood test to detect and eliminate breeders infected with Salmonella Pullorum probably did more than anything else to improve the quality of chicks.

Today, the NPIP is a voluntary Poultry Industry-State-Federal program for prevention and control of egg-transmitted, hatchery-disseminated poultry diseases, such as PD.  Participation in all NPIP programs is voluntary, but all flocks, hatcheries and dealers must qualify as “U.S. Pullorum-Typhoid Clean” before participating in other NPIP programs.  Participating flocks are listed in the official NPIP Directory of Participants which identifies states, flocks, hatcheries, and dealers that meet disease control standards specified in the Plan’s programs.  As a result, customers can buy poultry that has tested clean of certain diseases or that have been produced under disease-prevention conditions.  In addition, participating flocks have an approval number which can be used on shipping labels, certificates, invoices, and other documents.  Provisions for hobbyist and exhibition waterfowl, exhibition poultry, and gamebird breeding flocks are found in Subpart E of the NPIP.

Pullorum Disease is still common in Mexico, Central and South America, Africa, and parts of Asia.  S. Pullorum has adapted to chickens and typically produces acute systemic disease characterized by sudden death and high mortality only in very young chicks.  Infection of baby chicks frequently results in a persistent carrier state in clinically normal surviving chickens.  S. Pullorum persists and survives within the spleen and liver.   At the onset of egg production, physiological changes and a surge in sex hormones causes transient immunosuppression and allows a resurgence of infection.  During this period, numbers of S. Pullorum  bacteria increase in the liver and spleen of carrier hens and spread to the ovary and oviduct.  Infected hens have reduced egg production and eggs have reduced fertility and hatchability.  Reproductive tract infection of hens leads to shedding of S. Pullorum in up to one third of eggs laid and transmission to chicks that hatch from contaminated eggs.  Infected chicks shed S. Pullorum in their feces which contaminate feed, water, and litter.  Transmission to pen-mates occurs rapidly due to ingestion of contaminated feed, water, and litter.   S. Pullorum may survive for years in a favorable environment and may be carried by rodents.

Thanks to efforts by the NPIP, Pullorum Disease is now rare in the United States.  Even though chickens are the natural host, turkeys may be infected as well and infections are usually lifelong.  Occasionally, S. Pullorum is isolated from unusual hosts, such as ducks, guinea fowl, pheasants, quail, sparrows, canaries, bullfinches, parrots, and peafowl.  Even wild turkeys have yielded positive tests in a few instances.  No drug or combination of drugs will eliminate infection from a flock, so it is important to prevent vertical transmission from hens to chicks via contaminated eggs.  This goal is accomplished by identifying clinically normal carrier breeding chickens by testing with the stained-antigen whole blood test.  This test detects antibodies in the bloodstream which are directed against S. Pullorum.   To ensure adequate time for antibodies to develop in infected poultry, minimum ages at testing have been established.  Chickens should be more than 4 months of age when tested, turkeys more than 12 weeks of age, and upland gamebirds more than 4 months of age or after attaining sexual maturity, whichever comes first.   Minimum number of poultry to be tested is 30 birds per house, with at least 1 bird taken from each pen and unit in the house.  In houses containing fewer than 30 birds, all birds in the house must be tested.  The ratio of male and female birds tested must be the same as the ratio of male to female birds in the flock.  Positive tests must be reported to the State Animal Health Official (usually the State Veterinarian) and to the Official State Agency (NPIP office) in your state.