In 1990, the State of Michigan’s pseudorabies endemic area was home to 308 quarantined herds. This area of the southwest corner of the Lower Peninsula features diverse pork production modalities including large outdoor farrowing and rearing units and modern confinement buildings environmentally controlled. In 1992 the Pseudorabies and Swine Brucellosis Control and Eradication Act was passed. This act provided the necessary framework for the eradication of pseudorabies virus (PRV) but did not include provisions for funding. In 1994, additional funds were provided to employ an adequate field staff and by 1995, the field staff of two full-time USDA veterinarians was enhanced to include five full-time veterinarians with additional help provided by a state augmented fee-basis program that encourages private practitioners to participate. These additional human resources make it possible to maintain regular communications with owner/managers of all infected herds, to continue monitoring all non-infected herds in the stage II area, complete all tracebacks, and maintain adequate surveillance for the stage III area.

The past year has been very successful for pseudorabies eradication within the State of Michigan. Michigan recorded the most significant drop in quarantined herds since the start of its program, from 180 herds under quarantine in January 1995 to 110 quarantined in March 1996. Michigan has a split stage(II/III) status. Seventy-seven (77) counties are in stage III while six (6) counties located in the southwest corner of the lower peninsula comprise the stage II area. Within the stage III area there are only three infected herds (0.13 percent prevalence). Two of these border the endemic stage II area. One feedlot has tested negative, but receives animals from a positive multiplying unit. The other herd is a hunting preserve located in the center of the state (Ingham County). It will be completely depopulated by June 1996. This hunting preserve is believed to have been infected from an illegal movement of "Wild Russian" swine into the herd. Stage III status is maintained in this area through surveillance of cull breeding swine by a combination of slaughter sampling and first point testing. During the 12-month period of March 1995 through March 1996 testing was maintained at 24 markets and 10 slaughter establishments. The 4,349 total slaughter samples collected were supplemented with 7,522 samples collected at first point for a combined total of 11,349 samples (13.6 percent of stage III breeding herd). Four percent of these samples were determined to be serologically positive. Ninety-eight (98.4) percent of these positive samples were traced to their herd of origin or determined to have originated from another state.

The stage II area consists of six counties with 26.7 % of the Michigan swine herd and slightly more than 40% of the states breeding population. Of the 1,005 herds located in stage II only 110 are infected. The stage II area is distinctly divided between the northern and southern regions by state and national forest and land poorly suited for agriculture. The northern region of Ottawa and Allegan counties has 39 of its 406 herds infected. Of these 39 herds infected in this region, 13 are negative feedlots which are filled by positive multiplying units and only three herds of the 39 are circulating the virus. The remaining herds have controlled the virus and are removing positive animals from the herd through the natural culling process or an on accelerated schedule. The southern region of four counties has 599 herds, of which 77 are infected. Of the 77 herds infected in the southern region, eight are negative feedlots which are filled by a positive multiplying unit and only 26 herds are circulating the virus. The majority of the herds in the southern region are outdoor farrowing and rearing operations. Due to climatic variation, seasonal culling is common practice. These outdoor production sites eliminate PRV primarily through separation of the positive breeding herd while developing a negative replacement population. The positive breeding herds are often culled as a group following either the spring or fall farrowing. Michigan expects to cull the positive breeding groups from approximately 50 quarantined herds during 1996. The number of infected herds under quarantine should be halved by the end of 1996. When this occurs, Ottawa and Allegan counties will be eligible for Stage III recognition.

Michigan’s strategy for elimination of PRV is a three-pronged approach that includes:

1. Area Testing

2. Reduce herd to herd transmission and virus circulation within infected herds

3. Rapid Rollover

All negative herds in the Stage II area are tested every six months to be sure they remain negative. Quarantined herds are all required to maintain a herd plan for cleanup. These herds are visited every 3-6 weeks to monitor progress and adapt the current herd plan.

Probably the most challenging portion of the program is to decrease virus transmission and circulation. In order to decrease virus transmission, regular testing is essential. To help minimize virus activity, vaccination is strongly encouraged throughout the Stage II area. Currently, all except two of the infected herds are vaccinating for PRV and 136 non-infected herds are vaccinating because of the risks of PRV. In order to educate the producers about the PRV program, a public relations campaign has been initiated. This campaign consists of posters placed at strategic sites and flyers distributed to producers with the cooperation of local markets. These flyers are sent to producers by market operators as they make payment for animals marketed and serve to remind producers about vaccination procedures and protocols, regular testing and biosecurity. Rapid access to laboratory testing results has provided additional assistance in the control of virus circulation. The laboratory data base can now be accessed from the field via computer and lab results can be obtained the same day lab tests are completed. This allows quick decisions to be made about how to modify the herd plan and greatly enhances the ability to successfully prevent virus circulation.

Rapid Rollover is a voluntary process which often takes place following weaning. It is strongly encouraged by identifying all positive animals within an infected herd. By exposing their location within the herd, efforts can be made to keep the positive animals from direct contact with negative replacements and producers can make intelligent decisions about culling priority as regards pseudorabies. Another public relations campaign is planned for the Fall of 1996 to encourage owners of the remaining positive herds to eliminate PRV through rapid rollover.

A tool which has been of significant benefit to Michigan has been The Pseudorabies Technical Advisory Committee (TAC). This committee is made up of producers, industry representatives and Extension specialists. The committee serves as a resource and evaluates progress made in elimination of PRV from an infected herd. The committee assists in obtaining cooperation of herd owners, recommends adjustments to herd cleanup plans, or makes a recommendation to the Director of the Michigan Department of Agriculture for depopulation of infected herds. This committee has met with owners of four herds which were circulating the virus within the northern portion of the Stage II area. The first herd was released from quarantine within seven months following the TAC meeting. Owners of two herds have now established functioning herd plans. The most recent case involved a noncooperative herd owner with a continuous flow operation. This individual is presently cooperating to establish a working herd plan.

With adequate financial support, an enhanced field force, and most importantly with producer support, Michigan’s PRV program has made significant strides within the past year. Barring any unforeseen difficulties, Michigan expects to be declared free of pseudorabies by the year 2000 in accordance with the goals of the national program.