The distribution of strongylid egg and lungworm (Dictyocaulus eckerti) larval counts in adult female farmed red deer (Cervus elaphus), and the implications for parasite control.

Whilst healthy adult farmed red deer show little clinical indication of parasite infection, they may still be maintaining infection levels on the farm through low-level shedding of nematode eggs and lungworm larvae. This work was undertaken to establish the long-term distribution of parasite counts, to determine whether the higher counts seen in previous trials are repeatable across the same animals. All adult female red deer on a New Zealand North Island property were faecal sampled (n = 209), weighed, and body condition scored (BCS) on five sampling occasions from March - August 2021. Faecal samples were processed by modified Baermanns to recover, identify, and enumerate lungworm 1st stage larvae (FLC), and nematode faecal egg counts (FEC) were determined by mini-FLOTAC. Between animal variation for FEC was significant (p < 0.001); whilst many counts were low to zero, a few individuals were consistently shedding higher egg counts. Younger animals tended to have higher egg counts (p = 0.003), but there was no association between FEC and BCS (p = 0.22), and FEC and liveweight (p = 0.58). Modelling of the data indicated that 50% of the egg output resulted from 21% of the animals. Additionally, there was no significant association between the higher egg counts and the gastrointestinal nematode classification; 'long tails' (likely Oesophagostomum sp.) p = 0.76, and the Ostertagiinae complex p = 0.75. Lungworm counts tended to be very low (0 - 26 lpg); consistent with previous trials and literature in farmed adult deer. However, between animal differences were statistically significant (p < 0.001) indicating some animals were passing more larvae than others, and poorer conditioned animals (BCS 2.5) were significantly associated with higher larval count (p = 0.03). There was no relationship between larval count and age (p = 0.62) and larval count and liveweight (p = 0.22). Modelling indicates that 50% of pasture larval contamination was contributed by 15% of the animals. There was no correlation between nematode egg count and lungworm larvae count (p = 0.22). Adult deer may play an important role as a source of infection for young deer, therefore, an improved understanding of the distribution of infection is needed to improve parasite control.

Untargeted Multimodal Metabolomics Investigation of the Haemonchus contortus Exsheathment Secretome.

In nematodes that invade the gastro-intestinal tract of the ruminant, the process of larval exsheathment marks the transition from the free-living to the parasitic stages of these parasites. To investigate the secretome associated with larval exsheathment, a closed in vitro system that effectively reproduces the two basic components of an anaerobic rumen environment (CO2 and 39 °C) was developed to trigger exsheathment in one of the most pathogenic and model gastrointestinal parasitic nematodes, Haemonchus contortus (barber's pole worm). This study reports the use of multimodal untargeted metabolomics and lipidomics methodologies to identify the metabolic signatures and compounds secreted during in vitro larval exsheathment in the H. contortus infective third-stage larva (iL3). A combination of statistical and chemoinformatic analyses using three analytical platforms revealed a panel of metabolites detected post exsheathment and associated with amino acids, purines, as well as select organic compounds. The major lipid classes identified by the non-targeted lipidomics method applied were lysophosphatidylglycerols, diglycerides, fatty acyls, glycerophospholipids, and a triglyceride. The identified metabolites may serve as metabolic signatures to improve tractability of parasitic nematodes for characterizing small molecule host-parasite interactions related to pathogenesis, vaccine and drug design, as well as the discovery of metabolic biomarkers.

A model for the development of the free-living stages of Ostertagia leptospicularis, used in conjunction with on-farm egg count data, to estimate sources of pasture contamination on New Zealand red deer (Cervus elaphus) farms.

Farmed red deer face challenges from nematode parasites, primarily the pulmonary species Dictyocaulus eckerti and the complex of Ostertagiinae nematodes in the abomasum. Previous investigations on New Zealand deer farms identified limited seasonality in faecal egg and larval output in all stock classes, however, this does not indicate the key times of year those eggs develop into infective-stage larvae, and subsequently contribute to infection risk. A simple temperature-driven model was developed for the free-living stages of a representative deer-specific Ostertagiinae species; Ostertagia leptospicularis. The model was then validated using development data generated from seasonal plot trials. Using faecal egg counts and animal numbers from the previous monitoring study, and local weather data from each of the sampling farms, the relative contribution of each stock class to infective third-stage larvae population on pasture was estimated for each month of the year (2018-2019). The mixed-age adult females were the primary source of infective larvae on most of the sampled farms, principally due to their numerical dominance (i.e., venison breeding farms). The frequent anthelmintic use in the youngest stock class (< 12 months old) on some farms limited their output of eggs and hence their contribution to pasture infestation with infective larvae. However, the trends of larval development on pasture differed between the farms (due to local climate), and between the sampling years (2018-2019). Therefore, calendar-based application of anthelmintics to older stock is not recommended, as contribution to pasture contamination is multifactorial. The study provides a better understanding of deer parasite epidemiology on which to base improved management practices.

Seasonal output of gastrointestinal nematode eggs and lungworm larvae in farmed wapiti and red deer of New Zealand.

Gastrointestinal nematode parasites and lungworm are significant animal health issues for farmed wapiti and red deer (Cervus elaphus). Chronic infection with gastrointestinal nematodes, coupled with sporadic, often pathogenic, outbreaks of the lungworm Dictyocaulus eckerti in young deer has resulted in many farmers relying heavily on anthelmintic treatments. An improved understanding of the epidemiology of the parasites infecting farmed deer, including the sources and seasonality of pasture contamination on the farm, is essential to the development of more integrated and sustainable control programs. The numbers of strongyle nematode eggs and lungworm larvae shed by different stock classes (red and/ or wapiti mixed-age stags, mixed-age red hinds, rising 2-year-old red stags and mix-sex rising 1-year olds) were monitored monthly, across six farms located in different regions of New Zealand, from January 2018 to early 2020. Every month, 10 fresh on-pasture faecal samples were collected from each stock class and couriered overnight to the laboratory. Baermann apparatus to recover lungworm 1st-stage larvae were set up immediately on sample arrival. Faecal samples for nematode faecal egg count were stored at 4 °C until the number of strongyle eggs were counted by mini-FLOTAC. Additional information, including stocking density, grazing systems, and anthelmintic treatments, were also noted every collection month. Results indicate a relatively consistent proportion of animals within each stock class shedding low numbers of both gastrointestinal nematode eggs (about 75 %) and lungworm larvae (about 50 %) all year round. There was little apparent seasonality and few differences between farms (location). Further, the average number of eggs/larvae shed was also relatively constant across seasons and locations, within each stock class. Interestingly, there was little correlation between lungworm larval counts and egg counts suggesting that the same animals were not consistently shedding both parasites. The data indicate that in the presence of regular anthelmintic treatments to young deer (< 1 year old), the adult stock groups constitute a potentially significant source of pasture contamination, and hence future infection. However, these data do not incorporate the seasonal effects of weather on egg/larval development, nor the number of animals of each stock class on the farms. Incorporation of these variables will be necessary to identify the sources and timing of subsequent infection. This work is currently underway.

Host effects on the free-living stages of Haemonchus contortus.

A group of 5 lambs (Host 1-5) was infected with the same batch of Haemonchus contortus and after patency individual faecal samples were collected, separately incubated at 23 °C for 14 days and third stage larvae collected through Baermannisation. Life-history traits were compared between larvae from different hosts: the length of the larvae was measured by microscope image analysis, larval survival in water at 35 °C, larval susceptibility to ivermectin (EC50) in a migration assay, the proportion of larvae exsheathing in vitro and the proportion establishing to the adult stage in young lambs. For all traits there were significant differences between the host animals, with larvae from specific hosts following a consistent pattern of displaying the highest or lowest trait results. Compared with larvae from Host 1 the larvae from Host 5 were () shorter (741-692 µm, p < 0.05), had a longer median survival at 35 °C (3.6-6.4 days, p < 0.05), were less susceptible to ivermectin (EC50 of 1.2 v 4.5 µM, p < 0.05), exsheathed to a lesser degree (83.6-58 %, p < 0.05), but showed a higher establishment rate in the consecutive host (15.2-31.4 %, p < 0.05). Regarding the survival time, anthelmintic susceptibility (under most commercial farming practices) and establishment rate as indicators for fitness, the parasites populating Host 5 produced progeny of higher fitness. The findings indicate that the host animal of the parental parasite generation has a significant effect on the parasite progeny.

The effect on liveweight gain of using anthelmintics with incomplete efficacy against resistant Cooperia oncophora in cattle.

A replicated field trial was conducted to measure the effect on liveweight gain of failing to adequately control anthelmintic resistant populations of Cooperia oncophora and to determine whether populations, and hence production losses, increased with time. Eight mobs of 10 Friesian-Hereford calves were run on independent farmlets from January to December, over each of two years. All mobs were routinely treated with a pour-on formulation of eprinomectin every six weeks, which controlled parasites other than Cooperia. Four mobs also received six weekly treatments with an oral levamisole plus albendazole combination anthelmintic to control Cooperia. Liveweights, condition scores, faecal egg counts and larval numbers on pasture were measured throughout. In the first year animals treated with eprinomectin alone were 12.9 kg lighter in November than those treated with eprinomectin plus albendazole and levamisole, however, in the second year there was no difference between the treatment groups. The data, therefore, support the view that while C. oncophora is less pathogenic than other cattle parasite species it can still cause production losses when present in sufficient numbers. In the first year of the study, parasite load, as measured by faecal nematode egg count and larval numbers on herbage, tended to be higher and calf growth rates lower than in the second year. In both years, counts of infective larvae on herbage declined over winter-spring to be at low levels before mid-summer. This suggests that the carry-over of infection from one crop of calves to the next was relatively small and hence that the level of challenge to the young calves at the start of each year was largely due to the effectiveness of the quarantine treatments administered when the animals arrived on the trial site. Low survival of larvae on pasture between grazing seasons, resulting in small larval populations on pasture when drenching programmes start each summer, might help to explain the widespread development of anthelmintic resistance in this parasite under New Zealand grazing systems.