NAHLN Swine Surveillance Update

January 9, 2013 — 

The National Animal Health Laboratory Network NAHLN has collaborated with other groups within APHIS, the National Veterinary Services Laboratories, Wildlife Services, National Surveillance Unit, National Center for Animal Health Programs, and the National Center for Animal Health Emergency Management, to implement surveillance programs. Currently, NAHLN laboratories are participating in surveillance programs for bovine spongiform encephalopathy (BSE), classical swine fever (CSF), scrapie, swine influenza virus (SIV), and swine pseudorabies virus (PRV).

NAHLN laboratories play a critical role in VS surveillance programs by providing rapid standardized testing and results reporting for the above-mentioned diseases that are targeted in national animal disease surveillance initiatives. The following report highlights the testing results for FY 2012.

Classical Swine Fever Surveillance
The classical swine fever (CSF) surveillance program was initiated in 2006 to rapidly detect CSF virus and monitor the risk of introduction of the virus in the U.S. swine herd. The surveillance program targets five specific swine populations for testing:

• Sick pig submissions to veterinary diagnostic laboratories (VDLs)
• Slaughter swine with high risk of CSF exposure
• Feral swine
• Swine populations (including waste feeding operations)with high risk of CSF exposure in Florida, Texas, and Puerto Rico
• Swine highly suspicious for CSF and entered into a Foreign Animal Disease Investigation

NAHLN laboratories conduct CSF surveillance testing and NVSL's Foreign Animal Disease Diagnostic Laboratory (FADDL) is the CSF reference and confirmatory laboratory. In FY 2012, 19 NAHLN laboratories provided diagnostic testing for the CSF surveillance program.

The table below shows the number of animals tested for CSF by NAHLN laboratories in three surveillance target populations in FY 2011 and FY 2012. Feral swine test counts are not included here and waste feeder/high-risk data are not available.

CSF Surveillance Stream	FY 2011	FY 2012
Sick pigs submitted to VDLs	2,840	3,278
High risk slaughter swine	2,489	3,472
Total	5,329	6,750

Swine Influenza Virus Surveillance
The goals of the swine influenza virus (SIV) surveillance program are

1. to monitor the genetic evolution of endemic SIVs to better understand endemic and emerging influenza virus ecology,
2. make SIV isolates and associated epidemiologic data available for research and analysis, and
3. select proper isolates for the development of relevant diagnostic reagents, updating diagnostic assays, and vaccine seed stock products.

The program was initiated in May 2009 with a focus on monitoring the pandemic H1N1 2009 [pH1N1 (2009)] virus in swine. As the human health threat of pH1N1 (2009) declined in 2010, SIV surveillance efforts were re-focused on monitoring all current circulating SIVs. Also in 2010, an anonymous submission protocol was adopted to encourage more industry participation and increase the number of samples available for monitoring SIV in the U.S. swine herd. SIV surveillance efforts are targeted towards these three swine populations:

• Case-compatible sick pig submissions to VDLs
• Swine exhibiting influenza-like illness at first points of concentration or commingling events i.e., markets, fairs
• Swine populations that are epidemiologically linked to confirmed human cases involving SIV

NAHLN laboratories conduct SIV surveillance for the above-mentioned streams. The NVSL Diagnostic Virology Laboratory in Ames, Iowa is the SIV confirmatory laboratory.

SIV testing results reported by NAHLN laboratories in FY 2011 and FY 2012

The table below shows the number of herds (accessions) tested, number of influenza-positive herds, and number of herds with virus sub-typing results reported in FY 2011 and FY 2012.

Quarter/FY	Number of accessions tested	Number of influenza-positive accessions*	Number of accessions w/typing results reported
1/11	514	273	141
2/11	520	236	109
3/11	404	136	86
4/11	322	90	67
FY 2011 Total	1,760	735	403
1/12	553	227	130
2/12	517	177	81
3/12	658	284	161
4/12	951	291	272
FY 2012 Total	2,679	979	644

*Influenza-positive accessions are those with samples with positive matrix assay results

979 accessions had subtyping results reported in FY 2012. Mixed subtyping results (including multiple subtypes present and dual positives) were reported in 36 accessions.

The frequency of SIV virus subtypes collected as part of SIV surveillance in FY 2012 is as follows: H1N1 (n=217), H3N2 (n=218), H1N2 (n=173) and Mixed (n=36) [Note: If an accession had samples with more than one subtype, it is counted in each subtype group].

Pseudorabies Virus Surveillance
The pseudorabies virus (PRV) surveillance program was initiated in 2009 as an extension of USDA's successful PRV eradication efforts. The program gathers surveillance data to support three specific objectives: (1) rapidly detect PRV entry and infection in U.S. commercial swine, (2) demonstrate freedom from PRV in commercial herds, and (3) monitor domestic sources of PRV.

Targeted Populations (surveillance streams):

• Investigation and diagnosis of suspicious PRV cases
• Sick pig submissions to veterinary diagnostic laboratories (VDLs)
• Herds participating in routine serology and herd profiling
• Herds classified as high risk
• Herds with reported exposure to feral swine
• Cull sow-boars at slaughter
• Market swine at slaughter
• Feral swine

PRV-approved NAHLN laboratories test serologic samples from domestic swine for four targeted PRV surveillance populations: sick pig submissions, routine serology and herd profiling, high risk swine populations, and swine with known feral swine exposure. NAHLN laboratories also conduct PRV testing for domestic swine samples that are submitted as part of epidemiologic traceback investigations. Fourteen NAHLN laboratories conducted PRV surveillance sample testing in domestic swine in FY 2012 and two NAHLN laboratories conducted PRV testing on feral swine samples. The NVSL Diagnostic Virology Laboratory serves as the national reference laboratory and performs confirmatory testing for suspect and positive submissions for PRV.

In FY 2011, 335,290 and in FY 2012, 314,585 swine samples were tested under the PRV surveillance program in the following streams: diagnostic laboratory serologic submissions, sow-boar slaughter, and market slaughter. NAHLN laboratories tested 27,994 and 23,545 swine for the PRV diagnostic laboratory stream in FY 2011 and FY 2012, respectively.

Source: NAHLN Quarterly Newsletter