Therapeutic and persistent efficacy of moxidectin 1% nonaqueous injectable formulation against natural and experimentally induced lung and gastrointestinal nematodes in cattle

Strongyloides papillosus causes sudden death in weaned calves on New York dairies

CASE DESCRIPTION

Outbreaks of sudden death in apparently healthy weaned dairy calves due to Strongyloides papillosus parasitism were diagnosed on 2 separate and independent New York (NY) dairies.

CLINICAL FINDINGS

Most calves were found dead; however, 1 calf observed while dying showed signs of tachycardia, tachypnea, vocalization, and convulsions shortly before death. In 6 affected heifers that underwent post-mortem examination, precocious bilaterally symmetric mammary gland enlargement was seen. A portion of their parasitized living cohorts also demonstrated similar mammary gland enlargement. A diagnosis of S papillosus hyperinfection was made based upon the presence of high numbers of S papillosus ova in feces, and confirmation by S papillosus-specific PCR assays. Consistent histopathological findings in affected calves included generalized mammary gland vascular congestion, interstitial edema and hemorrhage with ductal hyperplasia. Mild multifocal cardiomyocyte degeneration was found in 5 of 14 calves examined. Factors believed to contribute to the parasite's environmental amplification and host hyperinfection included group housing on wood shavings and high environmental temperatures and humidity.

TREATMENT AND OUTCOME

Treatment of calves with doramectin pour-on stopped mortality and resolved the udder enlargement.

CLINICAL RELEVANCE

Similar outbreaks have previously been described in Japan and South Bohemia (Czech Republic), where researchers hypothesized that sudden death may be due to fatal arrhythmia caused by a parasite-associated cardiotoxin. This report highlights the importance of including S papillosus among the differential diagnoses for sudden death alone or together with precocious udder enlargement in calves kept in confinement housing.

Strongyloides spp. infections of veterinary importance

This paper reviews the occurrence and impact of threadworms, Strongyloides spp., in companion animals and large livestock, the potential zoonotic implications and future research. Strongyloides spp. infect a range of domestic animal species worldwide and clinical disease is most often encountered in young animals. Dogs are infected with Strongyloides stercoralis while cats are infected with different species according to geographical location (Strongyloides felis, Strongyloides tumefaciens, Strongyloides planiceps and perhaps S. stercoralis). In contrast to the other species, lactogenic transmission is not a primary means of infection in dogs, and S. stercoralis is the only species considered zoonotic. Strongyloides papillosus in calves has been linked to heavy fatalities under conditions of high stocking density. Strongyloides westeri and Strongyloides ransomi of horses and pigs, respectively, cause only sporadic clinical disease. In conclusion, these infections are generally of low relative importance in livestock and equines, most likely due to extensive use of macrocyclic lactone anthelmintics and/or improved hygiene. Future prevalence studies need to include molecular typing of Strongyloides species in relation to different hosts. More research is urgently needed on the potential zoonotic capacity of Strongyloides from dogs and cats based on molecular typing, information on risk factors and mapping of transmission routes.

Repurposing drugs for the treatment and control of helminth infections

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Drug repurposing continues to be the central drug discovery strategy for helminths.

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Most repurposed drugs come from veterinary medicine and known drug classes.

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Only a handful of drugs have advanced clinically.

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More collaborations and funding are needed to advance discoveries to the market.

Helminth infections are responsible for a considerable public health burden, yet the current drug armamentarium is small. Given the high cost of drug discovery and development, the high failure rates and the long duration to develop novel treatments, drug repurposing circumvents these obstacles by finding new uses for compounds other than those they were initially intended to treat. In the present review, we summarize in vivo and clinical trial findings testing clinical candidates and marketed drugs against schistosomes, food-borne trematodes, soil-transmitted helminths, Strongyloides stercoralis, the major human filariases lymphatic filariasis and onchocerciasis, taeniasis, neurocysticercosis and echinococcosis. While expanding the applications of broad-spectrum or veterinary anthelmintics continues to fuel alternative treatment options, antimalarials, antibiotics, antiprotozoals and anticancer agents appear to be producing fruitful results as well. The trematodes and nematodes continue to be most investigated, while cestodal drug discovery will need to be accelerated. The most clinically advanced drug candidates include the artemisinins and mefloquine against schistosomiasis, tribendimidine against liver flukes, oxantel pamoate against trichuriasis, and doxycycline against filariasis. Preclinical studies indicate a handful of promising future candidates, and are beginning to elucidate the broad-spectrum activity of some currently used anthelmintics. Challenges and opportunities are further discussed.

Pharmacokinetics assessment of moxidectin long-acting formulation in cattle

The plasma kinetics disposition of moxidectin following a subcutaneous administration with a long-acting formulation (Cydectin) 10%, Fort Dodge Animal Health, France) at the recommended dose of 1 mg kg(-1) body weight was evaluated in Charolais cattle breed (five females weighing 425-450 kg) for 120 days. Furthermore, its concentration was measured in hair for the same period. After plasma extraction and derivatization, samples were analysed by HPLC with fluorescence detection. Moxidectin was first detected at 1 h after treatment for plasma (2.00+/-1.52 ng ml(-1)) and at 2 days for hair (446.44+/-193.26 ng g(-1)). The peak plasma concentration (C(max)) was 55.71+/-15.59 ng ml(-1) and 444.44+/-190.45 ng g(-1) for plasma and hair, respectively. The mean calculated time of peak occurrence (T(max)) was 3.40+/-3.36 and 2 days for plasma and hair, respectively. The mean residence time (MRT) was 28.93+/-2.87 and 13.32+/-2.48 days for plasma and hair cattle. The area under concentration-time curve (AUC) was 1278.95+/-228.92 ng day ml(-1) and 2663.82+/-1096.62 ng day g(-1) for plasma and hair, respectively. At the last sampling time (120 days), the concentration was 1.91+/-0.26 ng ml(-1) and 0.69+/-0.52 ng g(-1) for plasma and hair, respectively. The bioavailability of this long-acting formulation of moxidectin is similar to that registered after subcutaneous administration of moxidectin in cattle at 0.2 mg kg(-1) body weight. For the first time the moxidectin pharmacokinetics parameters in hair after a subcutaneous administration was described. The moxidectin profile concentrations in hair reflected that registered in plasma. The previous studies of efficacy have to be correlated to the extended period of absorption and distribution by the LA formulation due to the fivefold higher dose rate in comparison with the 1% injectable formulation (0.2 mg kg(-1) body weight).

Lungworms of Ruminants

Several species of nematodes parasitize the respiratory tract of ruminants. Disease due to infection with these parasites occurs less frequently in North America than in other parts of the world but can be locally and regionally important. The life cycles, epidemiology, pathology, diagnosis and treatment of Dictyocaulus viviparus, Dictyocaulus filaria, and Muellerius capillaris are summarized in this article.

Efficacy of moxidectin 0.5% pour-on against naturally acquired nematode infections in cattle in the Mexican tropics

The efficacy of 0.5% moxidectin pour-on in cows with naturally acquired nematode infections was evaluated. The study was carried out in a ranch in Veracruz, Mexico. Four groups of 15 cows were randomly allocated. Animals in the treated group received 0.5% moxidectin pour-on at a dose of 0.5 mg/kg body weight on a single occasion. The other two groups remained as untreated controls. Fecal samples from all cattle were taken on days 0 (pre-treatment), 7, 14, 28 and 60 (post-treatment, PT). Fecal egg-counts were determined using a modified McMaster technique and fecal cultures were performed to identify gastrointestinal nematodes infected larvae (L(3)). Treatment with moxidectin was associated with a significant reduction in fecal trichostrongyle egg-counts compared with the controls; efficacy was 100% at 28 days PT. Haemonchus spp. and Strongyloides spp. were the two genera identified from coprocultures.