Caprine arthritis encephalitis and caseous lymphadenitis in goats: use of bulk tank milk ELISAs for herd-level surveillance

A large-scale study on the seroprevalence of small ruminant lentiviral infection in the Polish goat population

A large-scale study was carried out in a Polish goat population in 2014-2022 to determine the herd-level (between-herd) and within-herd seroprevalence of small ruminant lentivirus (SRLV) infection. A total of 8354 adult goats (aged >1 year) from 165 herds located in various regions of Poland were serologically tested using a commercial ELISA. One hundred twenty eight herds were randomly selected while 37 were enrolled based on convenience non-random sampling. At least 1 seropositive result was obtained in 103 / 165 herds. For all these herds the probability that they were truly positive (herd-level positive predictive value) was calculated. It was ≥ 90% in 91 seropositive herds and 73% to < 90% in 12 herds in which only 1-4 goats were seropositive (22 goats in total). The seropositive goats in the latter herds were retested using a different commercial ELISA and 14 goats (9 males and 5 females) from 9 herds were confirmed to be seropositive (serial testing). The true herd-level seroprevalence was estimated at 61% (95% confidence interval [CI 95%]: 53%-68%). It differed significantly between herd size classes (p = 0.003): the highest prevalences were found in the medium (51 - 100 adult goats) and large herds (>100 adult goats) - 72% (CI 95%: 56-84%) and 86% (CI 95%: 67%-95%), respectively, while prevalences in very small (≤ 20 adult goats) and small herds (21 - 50 adult goats) were 46% (CI 95%: 34%-59%) and 57% (CI 95%: 43%-70%), respectively. The true herd-level seroprevalence differed significantly also between geographical regions of Poland (p = 0.003), with the highest values in the north-western and the lowest in the southern region of the country. The true within-herd seroprevalence estimated using a Bayesian approach ranged from 0.7% to 100% with the median (IQR) of 42% (17%-84%), and did not vary significantly between herd size classes (p = 0.393) or geographical regions of Poland (p = 0.570). Concluding, SRLV infection is widespread in the Polish goat population, the north-western region of Poland is most extensively infected, and herds counting > 50 adult goats are more often infected.

Serological testing of an equal-volume milk sample - a new method to estimate the seroprevalence of small ruminant lentivirus infection?

BACKGROUND

In cattle attempts to evaluate within-herd prevalence of various infectious and parasitic diseases by bulk-tank milk (BTM) testing with ELISA have been made with moderate success. The fact that BTM is composed of variable and unknown volumes of milk from individual lactating animals weakens the relationship between numerical result of the ELISA and the within-herd prevalence. We carried out a laboratory experimental study to evaluate if a pooled milk sample created by mixing an equal volume of individual milk samples from seropositive and seronegative goats, henceforth referred to as an equal-volume milk sample (EVMS), would allow for accurate estimation of within-herd seroprevalence of caprine arthritis-encephalitis (CAE) using 3 different commercial ELISAs. By mixing randomly selected milk samples from seronegative and seropositive goats, 193 EVMS were created - 93 made of seronegative samples and 100 with the proportion of seropositive individual milk samples (EVMS_%POS) ranging from 1 to 100%. EVMS_%POS could be considered as a proxy for the within-herd seroprevalence. Then, OD of EVMS (OD_EVMS) of the 193 EVMS was measured using 3 commercial ELISAs for CAE - 2 indirect and 1 competitive.

RESULTS

The cut-off values of OD_EVMS indicating SRLV infection were determined. The regression functions were developed to link OD_EVMS with EVMS_%POS. A significant monotonic relationship between OD_EVMS measured with 2 commercial indirect ELISAs and EVMS_%POS was identified. Two regression models developed on this basis described approximately 90% of variability and allowed to estimate EVMS_%POS, when it was below 50%. High OD_EVMS indicated EVMS_%POS of > 50%.

CONCLUSION

Our study introduces the concept of serological testing of EVMS as a method of detecting SRLV-infected herds and estimating the proportion of strongly seropositive goats. Further field studies are warranted to assess practical benefits of EVMS serological testing.

Occurrence of CAE and CLA in Swedish Dairy Goats and Comparison of Serum and Milk as Sampling Material

Caprine arthritis encephalitis (CAE) and caseous lymphadenitis (CLA) are two infectious diseases affecting goat welfare and production throughout the world. There are no current data regarding their prevalence in Sweden, and the aim of this pilot study was therefore to estimate the occurrence in Swedish milk-producing goats, but also to assess the agreement between milk and sera as sample material for diagnosis and to investigate the association between the somatic cell count (SCC) in bulk milk and the occurrence of CAE and CLA. Serum, individual milk, and bulk-tank milk samples were collected from 214 dairy goats in 10 herds. All samples were analysed by ELISA to detect antibodies for CAE and CLA, and 14.6% of the goats were seropositive for CAE, whereas 19.3% of the goats were seropositive for CLA. The agreement between individual milk and serum samples was over 90% for both diseases and individual milk samples can therefore be considered as an alternative material for analysis in a future eradication programme. Based on the limited number of samples, there was also a significant correlation between bulk-milk test results and within-herd seroprevalence for both CAE and CLA. The SCC in bulk-milk samples was measured using a DeLaval cell counter. The medium SCC was 639,000 cells/mL and no association between SCC and CAE or CLA could be found. The results indicate that CAE and CLA are two common diseases in Swedish goat herds, but further studies based on a larger number of herds are needed to draw conclusions about the national prevalence. The results also indicate that milk can be used as a more cost-effective sampling media for diagnosing CAE and CLA compared to serology, which is the standard procedure today. Hopefully, the results can support the establishment of a successful programme to control the diseases, with the ambition to eradicate CAE and CLA in Sweden.

The epidemiological background of small ruminant lentivirus infection in goats from Romania

Background and Aim:

Caprine arthritis-encephalitis (CAE) is an economically significant viral disease of goats caused by a small ruminant lentivirus (SRLV) belonging to Retroviridae family. This study aimed to summarize current information on the epidemiological status of SRLVs infection in the population of goats from Romania and to point out the CAE incidence throughout the 2008-2018 periods.

Materials and Methods:

An exhaustive review of the papers published in the international literature concerning the epidemiological status of CAE in Romania was carried out using electronic databases, and available statistical data from the World Organization for Animal Health (OIE) regarding the incidence of the disease between 2008 and 2018 were analyzed.

Results:

The true individual-level seroprevalence of CAE was estimated in 13 of 42 counties (31%) and ranged from 0.4% to roughly 40%. One hundred eighty-two outbreaks from 14 counties (33%) were reported, with a peak in 2010.

Conclusion:

The findings sourcing in the literature are very scarce and show disagreement with the situation reported by the national veterinary authorities. Lack of SRLVs screening policies represents the main obstacle in limiting the spread of the disease. Romania’s National Sanitary Veterinary and Food Safety Authority should implement a program for diagnosis and surveillance of the disease to build a straightforward epidemiological picture that represents a prerequisite of any control and eradication program.

Transcriptome analysis of Corynebacterium pseudotuberculosis-infected spleen of dairy goats

Caseous lymphadenitis is a chronic disease of goats caused by Corynebacterium pseudotuberculosis (C.pseudotuberculosis) which causes great harm to the dairy goats industry. In order to obtain detailed information about the pathogenesis and host immune response in C.pseudotuberculosis-infected goats, in this study, the gene expression difference of spleen tissue after infection with C.pseudotuberculosis was analyzed by high-throughput sequencing. Transcripts obtained over 412 700 462 clean reads after reassembly were 21 343 genes detected, of which 14 720 were known genes and 7623 new genes were predicted. There were 448 up-regulated and 519 down-regulated differentially expressed genes (DEGs). Gene Ontology (GO) analysis indicated that all of the DEGs were annotated into biological process, cellular component and molecular function. Most of these unigenes are annotated in cellular processes, the cell and binding. KEGG analysis of the DEGs showed that a total of 8733 DEGs unigenes were annotated into 459 pathways classified into 6 main categories. Most of these annotated unigenes were related to immune system response to the infectious diseases pathways. In addition, 14 DEGs were verified by quantitative real-time PCR. As the first, in vivo, RNAseq analysis of dairy goats and C.pseudotuberculosis infection, this study provides knowledge about the transcriptomics of spleen in C.pseudotuberculosis-infected goats, from which a complex molecular pathways and immune response mechanism are involved in C.pseudotuberculosis infection.

Contagious agalactia monitoring in caprine herds through regular bulk tank milk sampling

Surveillance and control of Mycoplasma spp. responsible for contagious agalactia (CA) in caprine herds are important challenges in countries with a large small-ruminant dairy industry. In the absence of any clinical signs, being able to determine the potential circulation of mycoplasmas within a herd could help to prevent biosecurity issues during animal exchanges between farms and improve health management practices. The objective of this study was to determine whether regular sampling of bulk tank milk was suitable for such surveillance. Twenty farms were sampled once a month for 2 yr and CA-responsible mycoplasmas were detected by real-time PCR on DNA extracted from milk, using 3 different DNA extraction methods. The pattern of mycoplasma excretion in bulk tank milk was assessed over time and several herd characteristics were recorded together with any event occurring within the herds. In general, the results obtained with the different detection methods were comparable and mainly agreed with the culture results. Several patterns of excretion were observed but were not related to herd characteristics (size, breed, and so on). Recurrence of the same (sub)species and same pulsed-field gel electrophoresis subtype during the 2-yr period is indicative of the considerable persistence of mycoplasmas. This persistence was associated with intermittent excretion. In conclusion, bulk tank milk sampling could be valuable for controlling CA in caprine herds provided it is repeated several times, yet to be defined, per year and analyzed using an appropriate methodology and the right cut-off for interpretation.

Moving past serology: Diagnostic options without serum

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Traditional serology has moved beyond blood as a test medium.

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A number of different samples and tissues are now frequently used in veterinary diagnosis.

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Testing can be robust and accurate and opens up the field to a variety of new opportunities.

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Molecular testing allows direct testing for the agent on a variety of tissues and samples, and pools.

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Pooling of samples can allow for more efficient and cost-effective testing.

Detecting antibodies formed in serum in response to infection is the traditional function of serology. Diagnostic modalities have included complement fixation tests, agar gel immune-diffusion, radioimmunoassay, ELISA and immunofluorescence. More recent technology now allows for the direct detection of pathogens by PCR. This review details the options for diagnostic testing using specimen types other than serum, identifying the advantages and disadvantages of these options and providing evidence for more widespread use of these techniques and specimen types.