Environmental determinants predicting population vulnerability to high yellow fever incidence

Yellow fever (YF) is an endemic mosquito-borne disease in Brazil, though many locations have not observed cases in recent decades. Some locations with low disease burden may resemble locations with higher disease burden through environmental and ecohydrological characteristics, which are known to impact YF burden, motivating increased or continued prevention measures such as vaccination, mosquito control or surveillance. This study aimed to use environmental characteristics to estimate vulnerability to observing high YF burden among all Brazilian municipalities. Vulnerability was defined in three categories based on yearly incidence between 2000 and 2017: minimal, low and high vulnerability. A cumulative logit model was fit to these categories using environmental and ecohydrological predictors, selecting those that provided the most accurate model fit. Per cent of days with precipitation, mean temperature, biome, population density, elevation, vegetation and nearby disease occurrence were included in best-fitting models. Model results were applied to estimate vulnerability nationwide. Municipalities with highest probability of observing high vulnerability was found in the North and Central-West (2000-2016) as well as the Southeast (2017) regions. Results of this study serve to identify specific locations to prioritize new or ongoing surveillance and prevention of YF based on underlying ecohydrological conditions.

Estimating case fatality risk of severe Yellow Fever cases: systematic literature review and meta-analysis

BACKGROUND

Case fatality risk (CFR), commonly referred to as a case fatality ratio or rate, represents the probability of a disease case being fatal. It is often estimated for various diseases through analysis of surveillance data, case reports, or record examinations. Reported CFR values for Yellow Fever vary, offering wide ranges. Estimates have not been found through systematic literature review, which has been used to estimate CFR of other diseases. This study aims to estimate the case fatality risk of severe Yellow Fever cases through a systematic literature review and meta-analysis.

METHODS

A search strategy was implemented in PubMed and Ovid Medline in June 2019 and updated in March 2021, seeking reported severe case counts, defined by fever and either jaundice or hemorrhaging, and the number of those that were fatal. The searches yielded 1,133 studies, and title/abstract review followed by full text review produced 14 articles reporting 32 proportions of fatal cases, 26 of which were suitable for meta-analysis. Four studies with one proportion each were added to include clinical case data from the recent outbreak in Brazil. Data were analyzed through an intercept-only logistic meta-regression with random effects for study. Values of the I2 statistic measured heterogeneity across studies.

RESULTS

The estimated CFR was 39 % (95 % CI: 31 %, 47 %). Stratifying by continent showed that South America observed a higher CFR than Africa, though fewer studies reported estimates for South America. No difference was seen between studies reporting surveillance data and studies investigating outbreaks, and no difference was seen among different symptom definitions. High heterogeneity was observed across studies.

CONCLUSIONS

Approximately 39 % of severe Yellow Fever cases are estimated to be fatal. This study provides the first systematic literature review to estimate the CFR of Yellow Fever, which can provide insight into outbreak preparedness and estimating underreporting.

Multiple Genome Constellations of Similar and Distinct Influenza A Viruses Co-Circulate in Pigs During Epidemic Events

Swine play a key role in the ecology and transmission of influenza A viruses (IAVs) between species. However, the epidemiology and diversity of swine IAVs is not completely understood. In this cohort study, we sampled on a weekly basis 132 3-week old pigs for 15 weeks. We found two overlapping epidemic events of infection in which most pigs (98.4%) tested PCR positive for IAVs. The prevalence rate of infection ranged between 0 and 86% per week and the incidence density ranged between 0 and 71 cases per 100 pigs-week. Three distinct influenza viral groups (VGs) replicating as a "swarm" of viruses were identified (swine H1-gamma, H1-beta, and H3-cluster-IV IAVs) and co-circulated at different proportions over time suggesting differential allele fitness. Furthermore, using deep genome sequencing 13 distinct viral genome constellations were differentiated. Moreover, 78% of the pigs had recurrent infections with IAVs closely related to each other or IAVs clearly distinct. Our results demonstrated the molecular complexity of swine IAVs during natural infection of pigs in which novel strains of IAVs with zoonotic and pandemic potential can emerge. These are key findings to design better health interventions to reduce the transmission of swine IAVs and minimize the public health risk.

Evaluation of the Sensitivity of Reverse-Transcription Polymerase Chain Reaction to Detect Porcine Reproductive and Respiratory Syndrome Virus on Individual and Pooled Samples from Boars

Boar studs are continuously monitored for the presence of porcine reproductive and respiratory syndrome virus (PRRSV) by testing different biological samples by reverse-transcription polymerase chain reaction (RT-PCR). In most cases, samples are run in pools, even though the impact of pooling on the sensitivity of RT-PCR is unknown. The objective of this study was to evaluate the feasibility of using PCR on pooled samples through the estimation of the sensitivity of RT-PCR on different biological samples run individually, in pools of 3 and in pools of 5. Twenty-nine boars were inoculated with a low virulent PRRSV isolate. Serum, blood swab, and semen samples were obtained from each boar every 2 to 3 days for 2 weeks. Each sample was tested by RT-PCR undiluted or diluted 1:3 and 1:5 with negative samples. Eleven of the 29 boars did not appear to get infected from the inoculum, as evidenced by no seroconversion 15 days after inoculation. Data from the other 18 boars showed that serum was the best sample to detect PRRSV during acute infection, with the blood swab sample performing almost as well. Semen samples failed to detect PRRSV infection in most of the cases. Pooling samples at pool sizes of 3 and 5 resulted in a decrease in the sensitivity of RT-PCR. Sensitivity was reduced by 6% and 8%, respectively, when serum or blood swab samples were run in pools of 5. The impact of pooling on the sensitivity of PCR was higher in samples taken during the beginning of the viremic period.

Distribution and Diversity of Pathogenic Leptospira Species in Peri-domestic Surface Waters from South Central Chile

Background

Leptospirosis is a neglected zoonosis affecting animals and humans caused by infection with Leptospira. The bacteria can survive outside of hosts for long periods of time in soil and water. While identification of Leptospira species from human cases and animal reservoirs are increasingly reported, little is known about the diversity of pathogenic Leptospira species in the environment and how surveillance of the environment might be used for monitoring and controlling disease.

Methods and Findings

Water samples (n = 104) were collected from the peri-domestic environment of 422 households from farms, rural villages, and urban slums participating in a broader study on the eco-epidemiology of leptospirosis in the Los Rios Region, Chile, between October 2010 and April 2012. The secY region of samples, previously detected as pathogenic Leptospira by PCR, was amplified and sequenced. Sequences were aligned using ClustalW in MEGA, and a minimum spanning tree was created in PHYLOViZ using the goeBURST algorithm to assess sequence similarity. Sequences from four clinical isolates, 17 rodents, and 20 reference strains were also included in the analysis. Overall, water samples contained L. interrogans, L. kirschneri, and L. weilii, with descending frequency. All species were found in each community type. The distribution of the species differed by the season in which the water samples were obtained. There was no evidence that community-level prevalence of Leptospira in dogs, rodents, or livestock influenced pathogen diversity in the water samples.

Conclusions

This study reports the presence of pathogenic Leptospira in the peri-domestic environment of households in three community types and the differences in Leptospira diversity at the community level. Systematic environmental surveillance of Leptospira can be used for detecting changes in pathogen diversity and to identify and monitor contaminated areas where an increased risk of human infection exists.

Leptospirosis is a zoonotic disease that is caused by either direct contact with the urine of animals infected with pathogenic forms of Leptospira, or indirectly, through contact with contaminated water or soil. Because many people become infected through the environment, where the bacteria can live for many months if the conditions are suitable, we tested water samples from the peri-domestic area in twelve different communities from Los Rios region, Chile, to examine whether the Leptospira species were different in urban, rural village, and farm areas. We found that all three community types had L. interrogans, L. kirschneri, and L. weilii. No evident associations were seen between animal infection and the frequency or diversity of Leptospira. The proposed surveillance method has potential for systematic monitoring of surface waters that will help us better understand the importance of animal, climate, and environmental factors in the variation of Leptospira species present in a community in order to predict infection risk and inform prevention programs.

[Toxoplasmosis, a parasitic zoonoses prevalent in Chile: count and challenges]

BACKGROUND

Toxoplasmosis, cosmopolitan parasitic zoonosis often found in humans, is transmitted mainly by food and water, and is considered a significant risk of morbidity and mortality in pregnant women, newborns and immunocompromised patients.

OBJECTIVE

To identify the information about this zoonosis and its first reports in Chile.

MATERIALS AND METHODS

Review of publications in Pubmed, Mesh search of systematic reviews, case studies, cross-sectional studies, systematic reviews, meta-analysis and specialty publications. In addition, other publications in parasitology journals were analyzed.

CONCLUSIONS

There are reports of the presence of this disease in Chile for 60 years. During this time several differences in prevalence depending on geographic location, age and education level of the population have been detected. There is low epidemiological vigilance and lack of specific official preventive measures for this disease, despite the possible introduction of new parasite genotypes of an increased virulence and pathogenicity in the country through the importation of meat. New enigmas have arisen in relation to this disease associating it with Alzheimer, Parkinson's disease, autism, learning disabilities, among others.

Leptospirosis in Rio Grande do Sul, Brazil: An Ecosystem Approach in the Animal-Human Interface

BACKGROUND

Leptospirosis is an epidemic-prone neglected disease that affects humans and animals, mostly in vulnerable populations. The One Health approach is a recommended strategy to identify drivers of the disease and plan for its prevention and control. In that context, the aim of this study was to analyze the distribution of human cases of leptospirosis in the State of Rio Grande do Sul, Brazil, and to explore possible drivers. Additionally, it sought to provide further evidence to support interventions and to identify hypotheses for new research at the human-animal-ecosystem interface.

METHODOLOGY AND FINDINGS

The risk for human infection was described in relation to environmental, socioeconomic, and livestock variables. This ecological study used aggregated data by municipality (all 496). Data were extracted from secondary, publicly available sources. Thematic maps were constructed and univariate analysis performed for all variables. Negative binomial regression was used for multivariable statistical analysis of leptospirosis cases. An annual average of 428 human cases of leptospirosis was reported in the state from 2008 to 2012. The cumulative incidence in rural populations was eight times higher than in urban populations. Variables significantly associated with leptospirosis cases in the final model were: Parana/Paraiba ecoregion (RR: 2.25; CI95%: 2.03-2.49); Neossolo Litolítico soil (RR: 1.93; CI95%: 1.26-2.96); and, to a lesser extent, the production of tobacco (RR: 1.10; CI95%: 1.09-1.11) and rice (RR: 1.003; CI95%: 1.002-1.04).

CONCLUSION

Urban cases were concentrated in the capital and rural cases in a specific ecoregion. The major drivers identified in this study were related to environmental and production processes that are permanent features of the state. This study contributes to the basic knowledge on leptospirosis distribution and drivers in the state and encourages a comprehensive approach to address the disease in the animal-human-ecosystem interface.

Evaluation of performance of bacterial culture of feces and serum ELISA across stages of Johne's disease in cattle using a Bayesian latent class model

The objective of this study was to evaluate the performance of bacterial culture of feces and serum ELISA to correctly identify cows with Mycobacterium avium ssp. paratuberculosis (MAP) at heavy, light, and non-fecal-shedding levels. A total of 29,785 parallel test results from bacterial culture of feces and serum ELISA were collected from 17 dairy herds in Minnesota, Pennsylvania, and Colorado. Samples were obtained from adult cows from dairy herds enrolled for up to 10 yr in the National Johne's Disease Demonstration Herd Project. A Bayesian latent class model was fitted to estimate the probabilities that bacterial culture of feces (using 72-h sedimentation or 30-min centrifugation methods) and serum ELISA results correctly identified cows as high positive, low positive, or negative given that cows were heavy, light, and non-shedders, respectively. The model assumed that no gold standard test was available and conditional independency existed between diagnostic tests. The estimated conditional probabilities that bacterial culture of feces correctly identified heavy shedders, light shedders, and non-shedders were 70.9, 32.0, and 98.5%, respectively. The same values for the serum ELISA were 60.6, 18.7, and 99.5%, respectively. Differences in diagnostic test performance were observed among states. These results improve the interpretation of results from bacterial culture of feces and serum ELISA for detection of MAP and MAP antibody (respectively), which can support on-farm infection control decisions and can be used to evaluate disease-testing strategies, taking into account the accuracy of these tests.

Protective practices against zoonotic infections among rural and slum communities from South Central Chile

BACKGROUND

Despite well-recognized recommendations to reduce human exposure to zoonotic pathogens, the use of personal and herd-level protective practices is inconsistent in communities where human interactions with animals are common. This study assessed household-level participation in rodent- (extermination, proper food storage, trash disposal), occupational- (preventive veterinary care, boot-wearing, glove-wearing), and garden-associated (restricting animal access, boot-wearing, glove-wearing) protective practices in farms, villages, and slums in the Los Rios region, Chile, where zoonotic pathogens are endemic.

METHODS

Questionnaires administered at 422 households across 12 communities recorded household-level socio-demographic characteristics and participation in nine protective practices. Household inclusion in the analysis of occupational practices required having livestock and a household member with occupational exposure to livestock (n = 127), and inclusion in analysis of garden practices required having a garden and at least one animal (n = 233). The proportion of households participating in each protective practice was compared across community types through chi-square analyses. Mixed effects logistic regression assessed household-level associations between socio-demographic characteristics and participation in each protective practice.

RESULTS

Most households (95.3 %) reported participation in rodent control, and a positive association between the number of rodent signs in a household and rodent extermination was observed (OR: 1.75, 95 % CI: 1.41, 2.16). Occupational protective practices were reported in 61.8 % of eligible households; household size (OR: 1.63, 95 % CI: 1.17, 5.84) and having children (OR: 0.22, 95 % CI: 0.06, 0.78) were associated with preventive veterinary care. Among eligible households, 73.8 % engaged in protective practices when gardening, and species diversity was positively associated with wearing boots (OR: 1.27, 95 % CI: 1.03, 1.56). Household-level participation in all three protective practices within any exposure category was limited (<10.4 %) and participation in any individual protective practice varied considerably within and across community types.

CONCLUSIONS

The levels of participation in protective practices reported in this study are consistent with descriptions in the literature of imperfect use of methods that reduce human exposure to zoonotic pathogens. The wide differences across communities in the proportion of households participating in protective practices against human exposure to zoonotic pathogens, suggests that future research should identify community-level characteristics that influence household participation in such practices.

Isolation of Leptospira interrogans serovar Hardjoprajitno from a calf with clinical leptospirosis in Chile

BACKGROUND

Although Leptospira isolation has been reported in Chilean cattle, only serological evidence of serovar Hardjo bovis infection has been routinely reported. The present report provides characterization of the pathological presentation and etiology of a clinical case of leptospirosis in a calf from the Los Rios Region in Chile.

CASE PRESENTATION

In a dairy herd in southern Chile, 11 of 130 calves died after presenting signs such as depression and red-tinged urine. One of these calves, a female of eight months, was necropsied, and all the pathological findings were consistent with Leptospira infection. A urine sample was submitted to conventional bacteriological analysis together with highly specific molecular biology typing tools, in order to unravel the specific Leptospira specie and serovar associated with this clinical case. A significant finding of this study was that the obtained isolate was confirmed by PCR as L. interrogans, its VNTR profile properly matching with L. interrogans Hardjoprajitno as well as its specific genomic identity revealed by secY gen.

CONCLUSION

Leptospira interrogans serovar Hardjoprajitno was associated with the investigated calf clinical case. This information adds to the value of serologic results commonly reported, which encourage vaccination improvements to match circulating strains. In addition, this finding represents the first case report of this serovar in Chilean cattle.

Seroepidemiology of leptospirosis in dogs from rural and slum communities of Los Rios Region, Chile

Background

Leptospirosis is a zoonotic disease of global importance and often neglected as a public health problem due to lack of awareness, under-diagnosis and under-reporting. Animals serve as a source of transmission through the shedding of Leptospira in their urine. Because of their proximity to humans, dogs may play a role in human infections. In order to assess and mitigate leptospirosis in dogs and the risk of transmission to humans it is important to understand the epidemiology of leptospirosis under natural conditions. This study aimed to characterize leptospirosis in owned dogs from three distinct community types. Blood, dog and household data were collected from 265 dogs in 190 households from 12 communities representing farms, rural villages, and urban slums in the Los Rios region, Chile. Serologic profiles with a 20-serovar microagglutination test panel were obtained. Binomial and multinomial logistic regression models were used to evaluate the associations between spatial, ecological, socio-economic variables and overall seropositivity as well as seropositivity to serogroup Canicola.

Results

Results from 247 dogs with no history of vaccination were used. Overall seroprevalence was 25.1% (62/247) with significant differences by community type: 10.9% (9/82) in dogs from farms, 22.3% (21/94) from rural villages, and 45.1% (32/71) from urban slums (p <0.001). This trend by community type was also observed for dogs with evidence of seropositivity to the Canicola serogroup. Factors associated with seropositive dogs included dog density and precipitation two-weeks prior to sampling. Presence of Leptospira positive puddles collected from the peri-domestic household environment was also associated with increased seropositivity.

Conclusions

Results suggest that leptospirosis is actively maintained in the dog population in this study region with notably distinct patterns by community type. Dog populations from rural villages, and urban slums in particular, showed evidence of high levels of transmission probably as a result of the combined effects of dog living conditions as well as community-level ecological and environmental factors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0341-9) contains supplementary material, which is available to authorized users.

Detection of oocyst-associated toxoplasmosis in swine from southern Chile

Pork has been traditionally considered an important source of human Toxoplasma gondii infection. Pigs, as other meat-producing animals, can become infected by the ingestion of oocysts that are shed in the environment by infected cats or by the consumption of cysts present in tissues of infected mammals, commonly small rodents. The objective of this study was to investigate the level of T. gondii infection in swine from southern Chile that can be associated with the ingestion of oocysts and therefore exposure to a contaminated environment. A total of 340 serum samples from swine were obtained from three commercial slaughterhouses located in the Araucania and Los Rios Regions from southern Chile. Study animals originated from local farms, mainly small commercial producers, and the meat is sold locally. Overall, 8.8% (30/340) of the samples showed T. gondii-specific IgG antibodies. Of these sero-positive animals, 80% (24/30) were also positive for antibodies specific against the oocyst stage of the parasite, indicating that animals had been infected recently by the ingestion of oocysts. The observed results suggest a high level of environmental contamination with oocysts on the farms of origin. In addition to the food safety problems associated with the consumption of meat from infected animals, the high level of environmental contamination on the farm represents a direct health risk for people living and/or working on these farms. Consequently, there is a need to develop on-farm monitoring programmes and identify risk reduction strategies (food storage, water purification, rodent control and contact with cats) that are appropriate and cost-effective for informal and outdoor type of farms.

Knowledge, perceptions, and environmental risk factors among Jamaican households with a history of leptospirosis

BACKGROUND

Leptospirosis is a globally important zoonotic disease caused by pathogenic Leptospira, and outbreaks typically follow heavy rainfall and flooding. This study examined the knowledge and perceptions concerning leptospirosis, factors associated with environmental hygiene and sanitation, and the presence of Leptospira in water samples from households with or without a history of the disease in the parish of St. Mary, Jamaica.

METHODS

The study employed a cross-sectional design in 43 communities within the parish of St. Mary, Jamaica between September 2008 and March 2009. Households that had at least one confirmed case of leptospirosis during the 2005 or 2007 outbreaks were assessed for living conditions, environmental hygiene, and for knowledge and risk perceptions about leptospirosis. A parallel sampling scheme was used for households with no reported cases during the outbreak years.

RESULTS

Almost 97% of the participants reported having heard of leptospirosis; however, less than 40% of respondents from households with a history of leptospirosis agreed that leptospirosis was a problem in the parish. Among households without a history of leptospirosis, this perception was greater in urban/peri-urban households than in rural households (59% vs. 21%; p=0.04). Risk behaviors or living conditions were common; however, there was a high level of awareness about the health risks associated with flooding. Among households with history of leptospirosis, the perception that nothing can be done to control rodents was significantly higher (p<0.04) in rural (50%) than in urban/peri-urban (17.6%) households. Nine (4%) water samples were positive for Leptospira; 56% of these were from water stored for domestic purposes. Overall, residence in rural communities, presence of a garbage dump, and leptospiral DNA in water samples correlated with households with the history of the disease (p<0.01).

CONCLUSIONS

Education of rural communities regarding leptospirosis and its prevention through proper waste disposal and rodent control should be urgently initiated.

Household characteristics associated with rodent presence and Leptospira infection in rural and urban communities from Southern Chile

Rodents are well-recognized reservoirs of Leptospira, contributing to its maintenance in endemic areas and playing a role in the public health risk associated with the infection. This study sought to provide some insights into rodent populations from Chile and their Leptospira carriage. In total, 393 rodents were trapped in 177 households. Higher rodent counts were associated with year 2 of the study, rainfall, and number of rodent signs. There was an inverse correlation with the number of cats. The number of rodents was higher in villages compared with slums (rate ratio = 3.23) but modified by average household age. Eighty rodents (20.4%) tested positive for Leptospira: 19.7% on the farms, 25.9% in villages, and 12.3% in the slums. Prevalence was 22.5% in Mus musculus, 20.7% in Rattus rattus, 21.1% in wild rodents, and 10.3% in R. norvegicus. Seasonal and temporal effects were the major determinants of Leptospira infection in rodent populations.

A sero-survey of toxoplasmosis in farm and non-farm children from Wisconsin, United States, 1997-1999

BACKGROUND

Toxoplasmosis is among the most widespread and prevalent zoonosis in the world. People can become infected through ingestion of oocysts shed by felids or of tissue cysts contained in meat from infected animals. Acute infection can result in a wide spectrum of consequences, including flu-like illness and retinitis, as well as congenital infection in pregnant women. Severe disease can occur, especially if people are immunocompromised. Frequency of human infection varies substantially by region due to ecological, social, and cultural factors. The most recent nationwide prevalence estimates in children from United States were 3.6% in 6-11 year olds and 5.8% in 12-19 year olds. Because of the limited knowledge of the occurrence of common zoonotic pathogens in children in the United States, the objective of this study was to estimate the sero-prevalence of T. gondii-specific antibodies in children from the Marshfield area in Wisconsin and to examine the association between sero-positivity and farm living.

METHODS

Banked sera from 342 Wisconsin children collected in 1997-1999, aged 2 to 18 years, were tested for Toxoplasma gondii-specific IgG antibodies using ELISA. Recorded information included age, sex, and whether the child resided on a farm. Impact of assay accuracy, sensitivity and specificity, on sero-prevalence was examined using Bayesian methods.

RESULTS

Observed prevalence of T. gondii-specific antibodies was 10.8% (37/347). Adjusting for sensitivity and specificity of the assays yielded a prevalence estimate of 8.0% (95% probability interval: 4%-12.4%). Children living on a farm had a 5 times higher odds of T. gondii-specific antibodies than children not living on a farm (OR=5.08, 95% CI: 2.2-11.6).

CONCLUSION

Results suggest that even in apparently low-risk populations, the true extent of the infection in children is significant. In this study population, children living on farms were differentially exposed, with earlier and higher infection risk than children not living on farms. Findings highlight the need to increase awareness about toxoplasmosis acquired early in life and to improve our understanding of the ecology of T. gondii in rural environments from developed and developing countries.

Identification of a sporozoite-specific antigen from Toxoplasma gondii

Reduction of risk for human and food animal infection with Toxoplasma gondii is hampered by the lack of epidemiological data documenting the predominant routes of infection (oocyst vs. tissue cyst consumption) in horizontally transmitted toxoplasmosis. Existing serological assays can determine previous exposure to the parasite, but not the route of infection. We have used difference gel electrophoresis, in combination with tandem mass spectroscopy and Western blot, to identify a sporozoite-specific protein (T. gondii embryogenesis-related protein [TgERP]), which elicited antibody and differentiated oocyst- versus tissue cyst-induced infection in pigs and mice. The recombinant protein was selected from a cDNA library constructed from T. gondii sporozoites; this protein was used in Western blots and probed with sera from T. gondii -infected humans. Serum antibody to TgERP was detected in humans within 6-8 mo of initial oocyst-acquired infection. Of 163 individuals in the acute stage of infection (anti- T. gondii IgM detected in sera, or < 30 in the IgG avidity test), 103 (63.2%) had detectable antibodies that reacted with TgERP. Of 176 individuals with unknown infection route and in the chronic stage of infection (no anti- T. gondii IgM detected in sera, or > 30 in the IgG avidity test), antibody to TgERP was detected in 31 (17.6%). None of the 132 uninfected individuals tested had detectable antibody to TgERP. These data suggest that TgERP may be useful in detecting exposure to sporozoites in early T. gondii infection and implicates oocysts as the agent of infection.

Stability of Porcine reproductive and respiratory syndrome virus at ambient temperatures

The stability of Porcine reproductive and respiratory syndrome virus (PRRSV) was evaluated for temperatures appropriate to laboratory and field settings. Four North American (type 2) isolates (ATCC VR-2332, JA-142, MN-184, and Ingelvac(R) PRRS ATP vaccine virus) in cell culture medium (pH 7.5) were held at 1 of 4 temperatures (4, 10, 20, and 30 degrees C) and sampled over time. Samples were tested for infectious virus and total PRRSV RNA using median tissue culture infectious dose and quantitative reverse transcription polymerase chain reaction, respectively. The rate of loss of infectious virus was expressed in terms of the time required for virus concentration to decline by one half (i.e., half-life [T(1/2)]). Statistical analysis found that temperature, but not virus isolate, had a significant effect on T(1/2), and a single nonlinear regression model was derived to predict T(1/2) for temperatures between 0 and 50 degrees C: T(1/2) = 243.54 e((-0.109*TEMP)). In contrast to changes over time in the concentration of infectious virus, no change in the concentration of quantitative reverse transcription polymerase chain reaction-detectable PRRSV was detected at any temperature and contact time. This information will be of interest to persons working in laboratory or field situations in which the control of PRRSV is important.

Breed-associated variability in serum biochemical analytes in four large-breed dogs

BACKGROUND

Genetic background can influence the expected values of hematologic and serum biochemical analytes in domestic animal species.

OBJECTIVE

The purpose of this study was to determine if there are breed-related differences in serum biochemical variables in healthy purebred dogs of 4 breeds and to develop appropriate reference intervals.

METHODS

Alaskan Malamutes (n=59), Siberian Huskies (n=78), Golden Retrievers (n=90), and English Setters (n=77) were included in the study. The dogs had a median age of 42 months (range 10-112 months) and each breed included a mix of intact and neutered dogs of both sexes. Serum biochemical profiles (Olympus AU400e) were performed along with physical examinations, CBCs, and urinalyses to ensure dogs were clinically healthy. Differences in the values of biochemical analytes were assessed nonparametrically and reference intervals for all breeds combined were calculated as the central 95% percentile.

RESULTS

Significant differences were observed between breeds for all serum biochemical analytes except alkaline phosphatase, glucose, and chloride. The analyte ranges had a large degree of overlap between the different breeds.

CONCLUSIONS

Although many statistically significant breed-related differences in serum biochemical values were observed, the differences were small and unlikely to have clinical relevance or impact medical decision making.

Field estimation of the flock-level diagnostic specificity of an enzyme-linked immunosorbent assay for Avian metapneumovirus antibodies in turkeys

Routine serologic testing for Avian metapneumovirus (AMPV) infection of turkey flocks at slaughter is currently being used to monitor changes in the occurrence of AMPV infection in endemic areas and can also be used to detect the emergence of infection in currently unaffected areas. Because of the costs associated with false-positive results, particularly in areas that are free of AMPV infection, there is a need to obtain improved estimates of flock-level specificity (SP). The objective of this study was to estimate flock-level SP of a program to monitor AMPV infection in turkey flocks at processing using a standard enzyme-linked immunosorbent assay (ELISA). A study was carried out in which 37 AMPV-free flocks from 7 Midwest operations were followed serologically. Six percent, 3%, and 0.2% of total samples tested AMPV positive at 8 weeks, 12 weeks, and at processing, respectively. Overall, flock-level SP increased as the cutoff increased and as age increased. Flock-level SP at processing was 97%, if a cutoff of 1 was used (the flock was classified as positive if at least 1 sample tested positive), and 100%, if any other cutoff was used. Administration of antibiotics (P = 0.02) and vaccination for Bordetella avium (P = 0.08) were positively associated with the probability of (false) positive test results. These findings suggest possible cross-reactions with other infections and highlight the need to consider variable diagnostic performance depending on farm conditions.

Evaluation of surveillance protocols for detecting porcine reproductive and respiratory syndrome virus infection in boar studs by simulation modeling

Because porcine reproductive and respiratory syndrome virus (PRRSV) can be transmitted through semen, PRRSV-free boar studs need to be routinely monitored to rapidly detect any potential PRRSV introduction. However, current protocols for monitoring PRRSV in boar studs are diverse, sometimes very costly, and their effectiveness has not been quantified. The objective of this study was to evaluate the ability of different monitoring protocols to detect PRRSV introduction into a negative boar stud by using a simulation modeling approach. A stochastic transmission model was constructed to simulate the spread of PRRSV in a typical negative boar stud in the USA (herd size of 200 boars, 60% annual replacement) and the performance of monitoring protocols by using different sample sizes (10, 30, and 60 samples), sampling frequency (3 times a week, weekly, and biweekly), and diagnostic procedures (PCR on semen, PCR on serum, ELISA on serum, and both PCR and ELISA on serum). The monitoring protocols were evaluated in terms of the time from PRRSV introduction into the boar stud to PRRSV detection. Protocols that used PCR on serum detected the PRRSV introduction earlier than protocols that used PCR on semen, and these were earlier than those that used ELISA on serum. The most intensive protocol evaluated (testing 60 boars 3 times a week by PCR on serum) would need 13 days to detect 95% of the PRRSV introductions. These results support field observations, suggesting that an intensive monitoring protocol needs to be in place in a boar stud to quickly detect a PRRSV introduction.

Experimental quantification of the transmission of Porcine reproductive and respiratory syndrome virus

We conducted an experiment to determine the ability of vaccine against Porcine reproductive and respiratory syndrome virus (PRRSV) to reduce the transmission of PRRSV among pigs. At the end of the experiment, transmission rates did not differ significantly (P = 0.61) between the vaccinated and nonvaccinated pigs, the mean R-values being 0.598 (95% confidence interval [CI] 0.136 to 3.218) and 0.264 (95% CI 0.008 to 2.266), respectively. The unusually low rate of PRRSV transmission in both groups may not have provided a sufficient challenge to detect a vaccine effect. Several factors could affect the rate of PRRSV transmission: isolate virulence, inoculation dose, inoculation route, number of passages of the challenge virus in cell culture, and population size. Of these, isolate virulence appears to be the most important factor associated with the low transmissibility observed in this study. More studies comparing rates of transmission between PRRSV isolates with diverse levels of virulence are needed to better understand this association.

Effect of temperature and relative humidity on the stability of infectious porcine reproductive and respiratory syndrome virus in aerosols

The objective of this experiment was to describe the stability of airborne infectious porcine reproductive and respiratory syndrome virus (PRRSV) as a function of temperature and relative humidity. A cloud of infectious PRRSV was aerosolized using 24-jet Collison nebulizer into a dynamic aerosol toroid (DAT) maintained at a specific temperature and relative humidity. The PRRSV cloud within the DAT was sampled repeatedly over time using SKC BioSampler impingers and the total viral RNA (RT-PCR) and concentration of infectious PRRSV (TCID50) in the air samples was determined. As measured by quantitative RT-PCR, PRRSV RNA was stable under the conditions evaluated in this study. Thus, a comparison of viral RNA and Rhodamine B dye, a physical tracer, found no significant difference in the slopes of the lines. Titers of infectious virus were plotted by time and the half-life (T1/2) of infectious PRRSV was calculated using linear regression analysis. An analysis of the results showed that aerosolized PRRSV was more stable at lower temperatures and/or lower relative humidity, but temperature had a greater effect on the T1/2 of PRRSV than relative humidity. Based on these results, an equation was derived to predict the T1/2 of infectious airborne PRRSV for any combination of environmental temperature and relative humidity.

Factors affecting sensitivity and specificity of pooled-sample testing for diagnosis of low prevalence infections

Testing of pooled samples has been proposed as a low-cost alternative for diagnostic screening and surveillance for infectious agents in situations where the prevalence of infection is low and most samples can be expected to test negative. The present study extends our previous work in pooled-sample testing (PST) to evaluate effects of the following factors on the overall PST sensitivity (SE(k)) and specificity (SP(k)): dilution (pool size), cross-contamination, and cross-reaction. A probabilistic model, in conjunction with Monte Carlo simulations, was used to calculate SE(k) and SP(k), as applied to detection of bovine viral diarrhea virus (BVDV) persistently infected (PI) animals using RT-PCR. For an average prevalence of BVDV PI of 0.01 and viremia in each animal between 10(2) and 10(7)virusparticles/mL, the pool size associated with the lowest number of tests, and lowest cost, corresponded to eight samples/pool. However, the least-cost pool size (lowest number of tests) was associated with a SE(k) of 0.90 (0.75-1), which corresponded to a decrease of 0.04, relative to the assay sensitivity for a single sample. The SP(k) for the same pool size, considering the effect of detection of BVDV acutely infected animals and cross-contamination as source of false positive results, was 0.90 (0.85-0.95). The effect of a hypothetical cross-reacting agent was to markedly decrease SP(k), especially as the prevalence of the cross-reacting agent increased. For a pool size of eight samples and a prevalence of the cross-reacting agent of 0.3, SP(k) ranged from 0.67 to 0.86, depending on the probability that the assay would detect the cross-reacting agent. The methods presented offer a means of evaluating and understanding the various factors that can influence overall accuracy of PST procedures.