Peter R. Davies

Prevalence of salmonella in finishing swine raised in different production systems in North Carolina, USA

We compared the prevalence of salmonella in faecal samples from finishing pigs and in feed samples from swine herds in North Carolina, USA. Farms were either finishing sites using all-in/all-out management of buildings in multiple-site systems (14 farms) or farrow-to-finish systems using continuous flow management of finishing barns (15 farms). The two groups of herds differed with respect to several management variables. Salmonella were isolated from 565 of 2288 (24.6%) faecal samples and from at least 1 faecal sample on 24 of 29 (83%) farms. Predominant serotypes were S. derby, S. typhimurium (including copenhagen), S. heidelberg, S. worthington and S. mbandaka. Fewer farrow-to-finish farms were detected as positive compared with all-in/all-out farms. Prevalence was lower for pigs raised on slotted floors compared with all other floor types, and was highest for pigs raised on dirt lots. Modern methods of raising pigs in multiple-site production systems, using all-in/all-out management of finishing pigs, appear to have no benefit in reducing the prevalence of salmonella compared with conventional farrow-to-finish systems.

Comparison of methods for isolating Salmonella bacteria from faeces of naturally infected pigs

A series of experiments was conducted using faecal samples collected from commercial swine farms to evaluate the effects of variation in methods used for the detection of Salmonella bacteria. The primary objective of the studies was to compare the protocols routinely used in two laboratories in the USA. The studies included five experiments comparing the enrichment protocols used routinely in the respective laboratories (Method 1: 10 g faeces—buffered peptone water (BPW) pre‐enrichment—selective enrichment in Rappaport/Vassiliadis (RV) broth; Method 2: ∼1g faeces—primary enrichments in tetrathionate and Hajna GN broths—secondary enrichment in RV broth). The effects of enrichment temperatures (37 vs 42 °C) using RV broth (two experiments) and delayed secondary enrichment (four experiments) were also evaluated. Direct comparison of Method 1 and Method 2 indicated comparable results. However, when compared using faecal samples of equal weight, the Method 2 enrichment protocol was more sensitive for detecting Salmonella bacteria than the Method 1 protocol. Enrichment in RV at 42 °C was superior to 37 °C, particularly for samples that were pre‐enriched in BPW. Delayed secondary enrichment increased detection of Salmonella bacteria in swine faeces. These results highlight the imperfect sensitivity of culture methods, and the need for researchers to consider the sensitivity of bacteriological methods in the design and interpretation of the results of epidemiologic studies based on faecal culture

Seroprevalence of Toxoplasma gondii and Trichinella spiralis in finishing swine raised in different production systems in North Carolina, USA

We compared the seroprevalence of both Toxoplasma gondii and Trichinella spiralis in finishing pigs raised in different production systems in North Carolina, USA. Farms were either finishing sites using all-in/all-out management of buildings in multiple-site systems (14 farms) or farrow-to-finish systems using continuous-flow management of finishing barns or outdoor accommodation 14 farms). The two groups of herds differed with respect to several management variables. A total of 13 of 2238 samples (0.58%) were positive for antibodies to Toxoplasma gondii using the modified agglutination test. Of these, 12 were from 63 pigs sampled on a farm where finishing pigs were kept on pasture. Only one of 1752 (0.057%) samples from pigs kept in total confinement systems was seropositive. Only one pig of 2183 (0.046%) tested positive by ELISA for antibodies against T. spiralis. In this region, management practices in modern production systems appear to be adequate to virtually eliminate the risk of infection of finishing pigs with both T. gondii and T. spiralis.

Sarcoptic mange and production performance of swine: a review of the literature and studies of associations between mite infestation, growth rate and measures of mange severity in growing pigs.

Cost-effective control of sarcoptic mange requires knowledge of the effects of the disease on production. This paper presents a critical review of the literature on the association between sarcoptic mange and reduced production performance of swine. One of the difficulties in interpreting inconsistent findings among studies is lack of information about the severity of disease, which is likely to vary considerably. Lack of standard methods and failure to quantify disease severity preclude meaningful interpretation of experimental results in commercial production. Three experiments with growing pigs were conducted to evaluate associations between sarcoptic mite infestation and growth rate, and to assess pruritic behaviour and mite-induced lesions at slaughter as indices of mange severity. Sarcoptic mange was associated with increased pruritic behaviour and the presence of papular dermatitis at slaughter. Pruritic behaviour decreased over time despite reinfestation and may be subject to numerous behavioural influences. Growth rate tended to be slower in mange infested pigs, but a significant effect of mange infestation on average daily gain was found in only one trial, in which the severity of skin lesions at slaughter was greatest. These observations suggest that the production effects of mange infestation of growing pigs are variable. Evaluating dermatitis lesions at slaughter may be an objective means for assessing the severity of mange infestation and for relating experimental results to commercial swine production.

Using slaughter inspections to evaluate sarcoptic mange infestation of finishing swine.

Sarcoptic mange is one of the common swine diseases worldwide. Although mange-free populations can be established with caesarean derived stock, by herd repopulation programmes or by eliminating mange with ivermectin, mange remains prevalent in many countries. Field and experimental studies indicate that hypersensitive mange is detrimental to performance of growing pigs. Typically, producers tolerate mange infestation in their herds and control measures are often haphazard. This tolerance to mange infestation is attributable to the covert nature of the losses (reduced growth rate and feed efficiency without mortality) and to the fact that clinical signs of hypersensitive mange (pruritus) are usually viewed as normal. Lack of tools to evaluate mange severity in pigs and to demonstrate its importance has hindered the efforts of veterinarians to control the disease. Traditionally, veterinarians have used slaughter inspections to assess respiratory diseases such as enzootic pneumonia and atrophic rhinitis. Much of the value of slaughter inspections is as a tool with which veterinarians can educate and motivate their clients to improve disease control measures. The potential for evaluating hypersensitive mange by inspecting slaughtered pigs for lesions of papular dermatitis was recognised some time ago, but quantitative evaluation of the reliability of this approach has been lacking. We have conducted several studies in Australia, the USA, Canada, Europe and Latin America to evaluate associations between Sarcoptes infestation and the severity of papular dermatitis at slaughter, using a simple ordinal scale for classifying carcasses. Our initial field and experimental data in Australia indicated the specificity of localised dermatitis to be in the order of 75-80%, but that the generalised dermatitis was highly specific (> 98%) for mange. Subsequent studies in the US Midwest yielded almost identical results, and indicated that the method may also have some utility for surveillance of mange-free herds. Results from other locations invariably have shown significant associations between dermatitis lesions and mange infestation. Relative to other methods such as skin scrapings and monitoring pruritus, this method is simple and relatively objective, and should be considered for routine inclusion in slaughter inspection protocols.

Seroprevalence of Toxoplasma Gondii in Hogs in the National Animal Health Monitoring System (Nahms)

The objectives of this study were to assess the seroprevalence of Toxoplasma gondii in swine herds in the United States and to compare the prevalence of T. gondii in sows to that in market weight pigs. MATERIALS AND METHODS. We used sera collected in 1990 as a part of the National Animal Health Monitoring System (NAHMS) survey of 412 randomly selected swine herds in 17 states (Alabama, California, Colorado, Illinois, Indiana, Iowa, Maryland, Michigan, Minnesota, North Carolina, Nebraska, Ohio, Oregon, Pennsylvania, Tennessee, Virginia, Wisconsin). Blood samples from up to 10 sows and/or gilts were collected from each herd. For comparison, serum was also collected from market weight pigs in Tennessee in 1991-92 and North Carolina in 1994-95. Samples were stored frozen until analyzed for T. gondii antibodies by the modified agglutination test (MAT) using formalin fixed tachyzoites as antigen. Titers of 32 or greater were considered positive. RESULTS AND DISCUSSION. Twenty percent (679/3479) of the sows tested were positive. Positive hogs were present in each state except Colorado. Prevalence ranged from 12% positive in Illinois, Minnesota, and Nebraska to 34% positive in Alabama and Tennessee and 36% positive in Wisconsin. The Chi-square Goodness of Fit Test (p<.O5) indicated that Alabama, Ohio, Tennessee, and Wisconsin each had more positive hogs than one would expect by random chance and that Colorado, Illinois, Minnesota and Nebraska had fewer. Using fanns as the unit of analysis, 47% (194/412) of the fanns had a least one positive sow in the herd. Percentage of positive farms ranged from 22% and 23% in California and Nebraska to 73% and 74% in Alabama and Wisconsin, and 89% in Tennessee. The Chi-square Goodness of Fit Test (p<.OS) indicated that farms in Colorado, California, and Nebraska were less likely to have an infected hog living on the farm while farms in Ohio, Tennessee, and Wisconsin were more likely to have infected animals in the herd. These differences are probably more related to the number of small fanns, or the number of pigs raised outdoors in a state rather than to geographic location. In a previous investigation in Tennessee [ 11, sows associated with cats were 2.6 tunes more likely to be seropositive than sows not associated with cats; sows on sinall farms were 4.5 tunes more likely to be seropositive than sows on large fanns, and sows kept outdoors were 23 times more likely to be seropositive than sows kept indoors. Further investigations of the differences in swine husbandry practices between states and their role in the epidemiology of T. gondii in swine herds are warranted. A previous study [3] reported that 42% of the breeding hogs tested in a national seroprevalence survey in 1983-84 were seropostive for T. gondii. This compares to 20% seropositivity in this study. Both surveys employed the MAT. Perhaps the prevalence of T. gondii is decreasing in hogs thoroughout the country or possibly this d’ff , erence is a function of the sampling technique. The samples in the 1983-84 study were collected from swine that were commercially slaughtered: 613 animals that were perhaps past their prime as breeding stock. The animals sampled by NAHh4S were the present breeding stock and were probably younger with less time to acquire a T. gondii infection. In North Carolina, serum samples were collected on 29 farms from finishing pigs that were within one month of slaughter; 13/2312 were seropositive for T. gondii. In contrast, the seroprevalence of sows in North Carolina in the NAHMS study was 18% , and 39% of the farms had at least one positive sow. In Tennessee, samples were collected from 437 market-weight pigs. All of these animals were on UT experiment stations when sampled, although 297 were purchased as weanlings from farms throughout the state. The seroprevalence was 3% (12/437). This compares to 34% seropositivity in the sows in the NAHMS study where 89% of the farms had at least one positive sow. These numbers are also lower than the 23% prevalence reported in 11,229 market-weight pigs tested at slaughter and found seropositive in 1983-84 [3] with the MAT. Probably the main reasons for these differences are the age of the animals and the husbandry practices employed on the farms. The sows were older and had more time to acquire an infection. Many of the market weight pigs had minimal contact with the outdoors and cats and cat’s feces. The seropositive breeding animals probably do not play a significant role in the transmission of T. gondii to humans. These animals are older when sold and are made into processed meats which are usually highly seasoned, smoked, heated, or frozen. They are not sold as cuts of meat and, therefore, are only a danger to individuals in the processing plant handling the raw meat. The market-weight animals are sold as commercial cuts of pork and T. gondii has been isolated from pork tissues used for human consumption [4]. However, the prevalence in the finishing swine in our study was only between 1-3%. Another study [7] also found 3% of finishing swine in Illinois positive for T. gondii antibodies. Tissue cysts and bradyzoites are killed by heating meat thoroughly to 66 degrees C (150 degrees F) or by having it smoked or cured [2,6]. Also, freezing meat at -20 degrees C for 24 hours will destroy most cysts [ S ] . [This work was supported in part by a grant from The National Pork Producers Council.]

Evaluation of the monitoring of papular dermatitis lesions in slaughtered swine to assess sarcoptic mite infestation

We investigated the association between the presence of papular dermatitis and sarcoptic mite infestation in pigs slaughtered in southern Minnesota. Following dehairing, a sample of 30 pigs from each of 50 herds was inspected for papular dermatitis lesions. Herds were selected after being categorized into one of five categories according to the prevalence and severity of dermatitis lesions. Herd infestation with sarcoptic mange was determined by recovery of mites from ear scrapings of slaughtered pigs and also by survey of producer opinion. Mite infestation was detected in 28 herds (56%) and 215 of 1500 pigs (14%). Considerable variability in prevalence of positive scrapings, ranging from one pig (3%) to 19 pigs (63%), was found among infested herds. Prevalence of mite infestation was positively associated with severity of papular dermatitis lesions in groups. For individual pigs, estimates of the specificity of localized lesions ranged from 0.70 to 0.90. Generalized lesions appear highly specific (> 0.98) for sarcoptic mite hypersensitivity. Generalized lesions occurred in 36.7% of pigs from herds confirmed to be infested, compared with 0.4% of pigs in herds confirmed free from mange. Our date indicate that monitoring of dermatitis lesions in slaughtered pigs might be a useful test for sarcoptic mange in the Midwest, USA.

Risk prioritization of pork supply movements during an FMD outbreak in the US - Data and Materials

The Data.csv file contains the raw survey responses (location information collected by Qualtrics has been removed). Information about the variables and value labels can be found in the DataDictionary.txt file. The data can be read into the Analysis_Code.R file to perform analysis described in the paper and to create a static version of the Movements.html graph. Survey.pdf contains the survey questions with relevant skip and display logic.