Serological lessons from the bovine lungworm Dictyocaulus viviparus: Antibody titre development is independent of the infection dose and reinfection shortens seropositivity

Diagnostic challenges for Aelurostrongylus abstrusus infection in cats from endemic areas in Italy

BACKGROUND

The lungworm Aelurostrongylus abstrusus infects wild and domestic feline species worldwide and is considered a primary respiratory parasite of cats. Definitive diagnosis is based on the identification of first-stage larvae (L1s) released in faeces approximately 5 to 6 weeks after infection. More recently, serology has been shown to be a diagnostic alternative for A. abstrusus infection in cats. The present study aimed at evaluating the diagnostic performance of serological antibody detection compared to faecal examination for A. abstrusus infection in a population of cats with known infection status from endemic areas in Italy and to identify factors (larval scores, age, co-infections with other helminths) that may influence test sensitivity and specificity of serology.

METHODS

All cats resulting positive using the Baermann technique (n = 78) were tested with the A. abstrusus ELISA. An additional 90 serum samples from cats living in three geographical areas with infection prevalence > 10%, but that resulted negative on Baermann, were also tested.

RESULTS

Among 78 cats copromicroscopically positive for L1s of A. abstrusus (Group 1), 29 (37.2%) were seropositive in ELISA. Of the 90 cats from Group 2 (cats living in three geographical areas in Italy with A. abstrusus prevalence > than 10%, but negative on Baermann examination), 11 (12.2%) were positive on ELISA. The overall seroprevalence was 23.8%. There was no statistical difference either between average optical density (OD) values of cats excreting > 100 L1s vs. cats excreting < 100 L1s (0.84 vs. 0.66; P value = 0.3247) or comparing the OD values with age of infected cats. Few Baermann-negative cats positive for Toxocara cati or hookworms were seropositive, supporting lack of cross-reactivity to these nematodes.

CONCLUSIONS

Results from the present study suggest that relying solely on faecal examination may underestimate prevalence of A. abstrusus infection in cats and that field surveys based on antibody detection are useful for establishing true prevalence of infected and/or exposed animals.

Seroprevalence of Major Pasture-Borne Parasitoses (Gastrointestinal Nematodes, Liver Flukes and Lungworms) in German Dairy Cattle Herds, Association with Management Factors and Impact on Production Parameters

Simple Summary

Pasture-borne worm infections impact cattle health and productivity worldwide. The present study assessed exposure of dairy cattle herds to the three most important pastural parasites, i.e., gastrointestinal worms, liver flukes and lungworms, in three parts of Germany by measuring antibodies in bulk tank milk samples. The results show a high level of exposure to gastrointestinal worms, while antibodies against liver flukes were less frequently detected and lungworm-positive herds were rare. Regional and breed differences regarding parasite exposure were detected. In addition, the presence of antibodies was associated with access to fresh grass, access to hay, silage quality and deworming frequency. Furthermore, parasite exposure was significantly associated with a poor body condition across all regions. Parasite-exposed cows of high-performance breeds also produced on average less milk per year than dual-purpose breeds.

Abstract

Pasture-borne parasites adversely affect bovine health and productivity worldwide. In Europe, gastrointestinal nematodes, especially Ostertagia ostertagi, the liver fluke Fasciola hepatica and the lungworm Dictyocaulus viviparus represent the most important parasites of dairy cattle. The present study assessed exposure towards these parasites among 646 cattle herds in three parts of Germany during 2017–2019 via antibody detection in bulk tank milk (BTM). Overall, O. ostertagi levels indicative of production losses were detected in 41.2% (266/646; 95% confidence interval (CI): 37.4–45.1%) of BTM samples, while F. hepatica seroprevalence amounted to 14.9% (96/646; 95% CI: 12.2–17.9%). Only 2.3% (15/646; 95% CI: 1.4–3.9%) of samples were D. viviparus antibody-positive. Significantly lower O. ostertagi as well as F. hepatica seroprevalence was detected in dual-purpose breeds compared to high-performance breeds from the same region. Management factors related to parasite exposure included access to fresh grass and hay, silage quality and anthelmintic treatment. Furthermore, F. hepatica and O. ostertagi seropositivity was significantly associated with suboptimal herd-level body condition. Interestingly, the relationship between seropositivity and productivity differed between breed types. Negative impacts on milk yield were detected only in high-performance breeds, while O. ostertagi seropositivity was associated with a lower milk fat content in dual-purpose herds.

Association between Dictyocaulus viviparus bulk tank milk antibody levels and farmer-reported lungworm outbreaks

The lungworm Dictyocaulus viviparus can have a major impact on bovine health and productivity. Enzyme-Linked Immunosorbent Assays (ELISA), based on a recombinant Major Sperm Protein (MSP), have been developed to detect D. viviparus-specific antibodies in bulk tank milk (BTM). The objectives of this study are to assess the association between BTM optical density ratio's (ODR) and farmer-reported lungworm outbreaks based on the clinical sign "coughing" throughout the grazing season and to compare the sensitivity and specificity of two ELISAs under field conditions. The Hannover MSP-ELISA and the prototype Svanova MSP-ELISA were used for the detection of D. viviparus antibodies in BTM samples on 717 dairy farms during the 2018 grazing season. Assuming all herds to be truly lungworm infected, the results show that the Svanova ELISA had a lower sensitivity (40-65%) and specificity (75-90%) for the detection of D. viviparus infections in BTM compared to the Hannover ELISA, which had a sensitivity of 42% and 74% and specificity of 100% and 98% at a cut-off of 0.41 ODR and 0.25 ODR, respectively. Therefore, analyses of the associations between milk antibody levels and farmer-reported outbreaks during the 2018 and 2019 grazing season were assessed using the Hannover ELISA, on 717 and 634 farms, respectively. A positive association was found between a farmer-reported outbreak and having at least two consecutive positive BTM ODR's at a cut-off of 0.41 in 2018 (Odds Ratio (OR) = 5.5) and 2019 (OR = 2.8). Furthermore, there was a significant association between a farmer-reported outbreak and having a positive BTM ODR in August (OR 2018 = 4.4; OR 2019 = 2.8) and October (OR 2018 = 3.7; OR 2019 = 1.8). On the farms with a farmer-reported outbreak and positive BTM samples, over half (2018 = 77%; 2019 = 57%) of the positive ODR's were situated before the outbreak and 47% (2018) and 42% (2019) within 12 weeks before the outbreak. In conclusion, there is a positive association between farmer-reported outbreaks and the occurrence of a positive BTM sample at the cut-off of 0.41 ODR using the Hannover ELISA.

A novel pooled milk test strategy for the herd level diagnosis of Dictyocaulus viviparus

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First-lactation heifers have higher milk antibody levels than older animals.

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The optimum test is produced when 10 first-lactation heifer samples are pooled.

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The pooled test is superior to the bulk tank in diagnosing lungworm in a herd.

Current diagnostic methods for detecting the presence or absence of Dictyocaulus viviparus in dairy herds, are insensitive when based on detection of antibody levels in bulk tank milk (BTM). Here we present a novel technique to confirm the presence of the parasite based on a pooled-milk sample from 10 randomly selected first – lactation heifers (FLH). This study was run in two parts. First, a longitudinal study was performed to look at infection dynamics in milk samples across the grazing season using a prototype ELISA developed by Svanova (Boehringer-Ingelheim, Uppsala). We identified that mean ODR values in milk samples from FLH was significantly higher than that for older cows (0.13 versus 0.07 respectively, p < 0.001) suggesting that samples from the FLH cohort should be pooled to produce the test. Second, the pooled – milk test was evaluated on a cross-sectional survey of UK dairy herds (n = 25 grazing and n = 25 zero-grazing herds) to evaluate test performance under field conditions. The optical density ratio (ODR) cut-off value for our pooled-milk test using 10 FLH milk samples was optimal at a value of 0.16. Pooling 10 FLH samples created a sensitivity and specificity of 66.7% and 95.5% respectively. In comparison, whole-herd BTM samples had a maximum sensitivity of 37.5% and specificity of 63.6% at an ODR cut-off of 0.18. The area under the curve according to receiver-operative-characteristic (ROC) analysis was high for the 10-heifer test (0.87) but poor for the whole herd BTM testing (0.45). This study provides a more sensitive diagnostic test strategy for the screening of D.viviparus in dairy herds. Testing herds at the end of a grazing season would facilitate the planning of effective control measures, such as the use of the lungworm vaccination or strategic deworming, for the following grazing season. This may prove to be a useful test strategy for the diagnosis of a variety of parasitic diseases of livestock.

The effect of patent Dictyocaulus viviparus (re)infections on individual milk yield and milk quality in pastured dairy cows and correlation with clinical signs

Background

Infections with the bovine lungworm Dictyocaulus viviparus might lead to reduced milk production and detrimental impacts on milk quality resulting in considerable economic losses in dairy farming.

Methods

In the presented field study, 1988 faecal samples were collected from 1166 Black and White dairy cows allocated in 17 small and medium-sized German grassland farms. Faecal samples were collected in summer and autumn 2015 to assess D. viviparus larvae excretion. Test-day records were used to estimate the association between patent D. viviparus infections in individual cows and the milk production parameters milk yield, milk protein and milk fat content by using linear mixed models. Bulk tank milk (BTM) samples from each farm and individual milk samples from those cows which were excreting larvae in summer were collected in autumn. In addition, occurrence of the clinical symptom “coughing” was noted in individual cows during autumn sampling to determine its association with patent lungworm infections.

Results

Patent D. viviparus infections were found on 23.5% (4/17) of farms with a prevalence at the individual cow level of 0.9% (9/960) in summer and 3.4% (35/1028) in autumn. No BTM sample exceeded the BTM ELISA cut-off value of 0.410 optical density ratio (ODR), the mean value was 0.168 ODR. Only one individual milk sample exceeded the individual milk ELISA cut-off value of 0.573 ODR (mean value of 0.302 ODR). A patent D. viviparus infection status was associated with a lower average daily milk yield of 1.62 kg/cow/day (P = 0.0406). No significant association was found with milk protein or fat content representing milk quality parameters. Coughing was observed in 5.9% (61/1028) of cows. Of the coughing cows, only 4.9% (3/61) had a patent lungworm infection. Fisher’s exact test showed no significant difference between infected and non-infected coughing cows.

Conclusions

Farmers and veterinarians should be aware that patent lungworm (re)infections in dairy cows reduce milk yield, despite the absence of clinical signs. Furthermore, if dairy cows present with coughing, other differential diagnoses need to be considered in addition to dictyocaulosis.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2602-x) contains supplementary material, which is available to authorized users.