The Australian paralysis tick occupies a unique and feared position among the country’s parasites. Found along the humid eastern seaboard, I. holocyclus feeds on a wide range of mammals, and its adult females secrete a potent neurotoxin known as holocyclotoxin while taking a blood meal. In young calves and other naïve animals that have not developed tolerance, this toxin can cause progressive, ascending paralysis that may prove fatal if the tick is not found and removed. For livestock producers, the tick represents both an animal welfare hazard and an economic burden, particularly in dairy and beef operations where calves graze on tick-infested pasture during the warmer months when tick activity peaks.

Existing control options leave a significant gap. Acaricide treatments used against other cattle parasites, such as the cattle tick Rhipicephalus australis, are not always reliably effective against I. holocyclus, and their persistence can be too short to cover the weeks during which calves remain vulnerable. Products registered specifically for paralysis tick control in cattle are limited, and no pour-on formulation had been approved for this purpose in Australia. Pour-on applications are attractive in practice because they avoid the stress and labor of injectable handling regimes or labor-intensive individual tick searches across large herds. Against this backdrop, fluralaner, a member of the isoxazoline class of ectoparasiticides, appeared to be a promising candidate. Isoxazolines act on the nervous systems of arthropods by blocking ligand-gated chloride channels, producing paralysis and death of the parasite, and fluralaner has already demonstrated efficacy against I. holocyclus in dogs and cats. The compound is characterized by systemic distribution and prolonged persistence in the host, which is precisely the profile needed for a long-acting tick control product.

To test the formulation rigorously, the researchers designed two randomised, controlled and blinded studies using a total of 40 healthy male dairy calves, with 20 calves allocated to each study. Within each study, calves were randomly assigned either to an untreated control group or to a fluralaner-treated group, with ten animals in each arm. On Day 0, treated calves received a single topical application of the fluralaner pour-on solution at a minimum dose of 2.5 milligrams per kilogram of body weight, applied along the topline in the manner typical of commercial pour-on products. To establish a pre-existing infestation that would allow the therapeutic effect to be measured, calves were experimentally infested with unfed adult female I. holocyclus ticks on Day −1, one day before treatment. Study 1 used an infestation challenge of ten ticks per calf, while Study 2 used fifteen ticks per calf, providing a slightly heavier parasite burden in the second trial.

The assessment protocol distinguished carefully between therapeutic and persistent efficacy. Therapeutic efficacy, the ability of the treatment to kill ticks already on the animal, was evaluated 48 hours after treatment by comparing live tick counts between treated and control calves. Ticks were first assessed in situ at 24 hours post-treatment, and then counted and removed at 48 hours. Persistent efficacy, the ability of the treatment to protect against new infestations, was assessed by re-infesting all calves weekly with fresh adult female ticks for up to six weeks after treatment. Following each re-infestation, ticks were assessed in situ at 48 hours and then counted and removed at 72 hours, with live tick counts in treated calves compared against those in untreated controls at every time point. This weekly challenge design is demanding, because it tests whether the drug remains at acaricidal concentrations in the skin and blood long after a single application.

The results were striking, particularly for persistent protection. Against the pre-existing infestation, therapeutic efficacy measured at 48 hours post-treatment was 95.5 percent in Study 1 and 69.1 percent in Study 2, indicating that the pour-on formulation killed the substantial majority of ticks already feeding on the treated calves, though the effect against established infestations was somewhat more variable in the second study. The persistent efficacy, however, was remarkable: at 72 hours after each weekly re-infestation, efficacy remained at 100 percent throughout the assessment period in Study 1, and ranged from 98.6 to 100 percent in Study 2. In practical terms, this means that for several weeks after a single application, virtually no tick that attempted to feed on a treated calf survived long enough to complete a blood meal, which is the critical threshold for preventing toxin delivery.

Statistical analysis reinforced the biological picture. Fluralaner-treated calves carried significantly fewer live ticks than untreated controls at all 72-hour assessments through to Week 4, with P values of 0.002 or lower. Beyond Week 4, efficacy declined below the 95 percent benchmark in both studies, marking the practical limit of protection from a single dose under the conditions of these trials. The authors therefore concluded that a single topical administration of the fluralaner pour-on solution provided control of existing I. holocyclus infestations and sustained protection against re-infestation for 28 days in calves under controlled experimental conditions. The four-week window aligns well with common livestock management cycles, suggesting that a monthly treatment schedule during the tick season could keep calves protected through the period of peak risk.

Safety and tolerability, always central considerations for a new use of a veterinary medicine, were also assessed. The treatment was well tolerated across all 20 treated calves, with only one mild, localized skin reaction observed at the application site. No other adverse effects were reported. The studies were conducted with animal ethics approval from the New South Wales Department of Primary Industries Secretary’s Animal Care and Ethics Committee for Study 1 and the Wongaburra Research Centre Animal Ethics Committee for Study 2, and under an Australian Pesticides and Veterinary Medicines Authority permit for small-scale trials with agricultural and veterinary chemicals. The statistical analysis was performed by Fangshi Sun of Merck Animal Health, and the studies were funded by Merck Animal Health, with both authors employed by MSD Animal Health Australia, a disclosure that readers should weigh when interpreting the uniformly positive results.

The significance of the work extends beyond the specific numbers. A pour-on isoxazoline product with a month-long duration of action against paralysis ticks would address several practical limitations of current approaches. It would reduce the frequency of handling, lower the labor required for tick surveillance in susceptible calves, and provide a margin of safety against the toxin that individual tick searches cannot guarantee, since a single engorging female can paralyze a small calf. The systemic mode of action also means protection does not depend on the tick contacting a treated patch of skin, as is the case with some repellent or topical products. Because fluralaner has an established track record against I. holocyclus in companion animal medicine, the class itself is well characterized, although dose rates, formulations and withdrawal considerations for cattle differ substantially from those for dogs and cats.

Important caveats remain before the findings translate into on-farm practice. The trials were conducted under controlled experimental conditions with fixed infestation pressures of laboratory-placed adult female ticks, which do not fully reproduce the variable exposure, weather, and mixed tick populations of commercial pastures. Efficacy against established infestations was lower in the heavier-challenge study, and protection fell below 95 percent after four weeks, so treatment intervals would need careful management. Most importantly, the authors explicitly state that at the time of publication, paralysis tick control is not an approved indication on the Australian APVMA registration of the fluralaner pour-on solution for cattle, meaning veterinarians and producers must await regulatory action before the product can be used for this purpose. Nevertheless, the study provides a robust evidence base for that next step, and it will be watched closely by producers in eastern Australia, where each tick season brings the risk of losing calves to one of the world’s most potent natural toxins.

Subject of Research: Efficacy of a fluralaner pour-on acaricide against experimental Ixodes holocyclus infestations in calves

Article Title: Efficacy of a single treatment of a fluralaner pour-on solution for cattle (Exzolt) against experimental infestations of Ixodes holocyclus on calves

Article References: de Asis, E., & Fisara, P. (2026). Efficacy of a single treatment of a fluralaner pour-on solution for cattle (Exzolt) against experimental infestations of Ixodes holocyclus on calves. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07636-2

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07636-2

Keywords: Australian paralysis tick, Ixodes holocyclus, fluralaner, isoxazoline, calves, cattle, acaricide, pour-on treatment, holocyclotoxin, Parasites & Vectors, tick control, veterinary parasitology

Ethiopia’s stakes in this question are enormous. The country holds Africa’s largest livestock population, with a national herd of roughly 70.3 million cattle, 42.9 million sheep, 52.5 million goats and 8.1 million camels according to the Central Statistics Agency’s 2021 sample survey. Livestock supply animal protein, draft power for cultivation, transport, export earnings, organic fertiliser and household fuel, and they act as a financial buffer during crop failures. The sector contributes up to 40 percent of agricultural gross domestic product, nearly 20 percent of total GDP and about 20 percent of foreign exchange earnings. Any disease that quietly erodes calf growth therefore carries consequences that ripple through the national economy.

Coccidiosis is precisely such a disease. It is caused by Eimeria species, intracellular protozoa that invade and destroy the epithelial cells of the intestinal tract. Clinical cases present with diarrhoea, weight loss, fever, anorexia, emaciation and sometimes haemorrhagic dysentery and death. More insidiously, the majority of infections remain subclinical, yet they still reduce feed intake, impair feed conversion efficiency and slow weight gain. Subclinical cases account for more than 95 percent of total production losses attributed to the disease, and annual global losses have been estimated to exceed US$400 million. Affected calves may suffer growth retardation of up to two months, a delay that reshapes the lifetime productivity of a dairy animal.

More than a dozen Eimeria species have been described in cattle and buffalo, with Eimeria bovis, Eimeria zuernii and Eimeria auburnensis most frequently reported. E. bovis and E. zuernii are the most pathogenic, capable of severe disruption of intestinal absorption and substantial morbidity and mortality. The parasites display marked host specificity, restricting transmission largely to cattle. Calves acquire infection by ingesting sporulated oocysts shed in faeces, a process accelerated by communal housing, overcrowding and contaminated udders. The oocysts are environmentally formidable, surviving prolonged freezing at temperatures as low as minus 18 degrees Celsius and requiring only warmth and moisture to sporulate into their infective form over days to weeks.

The new study focused on Haramaya District, located roughly 500 kilometres east of Addis Ababa and 18 kilometres west of Harar, at altitudes between 1,600 and 2,100 metres. The area receives bimodal rainfall of approximately 492 to 866 millimetres annually, with temperatures ranging from 5.2 to 24 degrees Celsius, and mixed crop-livestock farming dominates. Haramaya town was purposively selected as the major urban dairy centre, while five surrounding kebeles, the local administrative units, were chosen by simple random sampling to represent peri-urban production systems. A preliminary census of all farms keeping calves under twelve months produced the sampling frame, from which individual calves were drawn by lottery, giving every eligible animal an equal chance of inclusion and minimising selection bias.

Fieldwork ran from November 2024 to May 2025, with sampling conducted during the dry season. Fresh faecal samples were collected directly from each calf, sealed in labelled leak-proof containers and transported in insulated cool boxes at roughly 4 to 8 degrees Celsius. In the laboratory, three grams of each sample were homogenised with 40 millilitres of sugar flotation solution of specific gravity 1.27, centrifuged at 1,500 revolutions per minute for five minutes, and the resulting surface film was examined microscopically at 40 times magnification for the characteristic oocysts. The sample size of 284 was calculated from an expected prevalence of 24.4 percent drawn from earlier work in the area, using standard epidemiological formulas for a 95 percent confidence interval.

The results showed that host characteristics and farm conditions mattered more than genetics or geography. Prevalence rose with age: calves aged six to under twelve months carried an infection rate of 27.3 percent, significantly higher than the 17.2 percent seen in calves younger than six months, a pattern the authors attribute to cumulative exposure to contaminated feed, water, bedding and animals over time. Calves in poor body condition showed a prevalence of 29.7 percent against 18.6 percent in those in good condition, though the cross-sectional design prevents any conclusion about whether malnutrition predisposed the animals to infection or the parasite drove them into decline. Farm hygiene produced the starkest contrast: 31.3 percent of calves on farms rated as poorly hygienic were positive, compared with 14.6 percent on well-kept farms.

Several expected risk factors, by contrast, proved statistically irrelevant. Sex was not associated with infection, suggesting male and female calves faced similar exposure. Breed made no significant difference, with crossbred Holstein Friesian crosses at 26.5 percent and local breeds at 21.3 percent, a finding consistent with the view that environmental and management conditions outweigh genetic susceptibility. Neither the management system, whether intensive housing or extensive free grazing, nor the individual kebele of origin was significantly linked to infection, implying that the crucial variable is not how a farm is organised but how cleanly it is run. Accumulated faeces, wet bedding, poor drainage and unhygienic feed and water troughs evidently matter more than the label attached to the production system.

The 22.5 percent prevalence sits squarely within the range reported across Ethiopia, matching figures from Dire Dawa, Wolaita Sodo, South Wollo, Bahir Dar and even Egypt, while remaining lower than rates of 62.5 percent in Asella and 68.1 percent in Addis Ababa and Debre Zeit. Earlier regional work has catalogued the local parasite fauna in detail, identifying six Eimeria species around Haramaya, with E. bovis and E. zuernii most common and mixed infections frequent. The present study, however, stopped at oocyst detection and did not identify species, so the reported figure should be read as the proportion of calves carrying detectable coccidia rather than as species-specific infection. The authors flag this as a key limitation and call for sporulation-based morphological identification and molecular characterisation, together with quantitative oocyst counts, in future work.

For farmers and veterinarians in East Hararghe, the practical message is unusually clear. Since hygiene status was the strongest modifiable predictor of infection, interventions targeting calf pen cleanliness, regular manure removal, dry and clean bedding, adequate drainage and well-maintained feeding and watering facilities could substantially cut exposure to Eimeria oocysts. Combined with routine health monitoring, attention to calf nutrition to protect body condition, and awareness that older calves accumulate exposure over months, such measures offer a low-cost path to reducing the hidden burden of subclinical coccidiosis. The authors recommend longitudinal follow-up studies with broader geographic coverage to clarify infection dynamics and quantify production losses, steps that would help convert these epidemiological findings into concrete gains for Ethiopia’s dairy-dependent rural households.

Subject of Research: Prevalence and risk factors of coccidiosis in calves in eastern Ethiopia

Article Title: Prevalence of Coccidiosis and Its Associated Risk Factors Among Calves in and Around Haramaya Town, Eastern Hararge, Oromia, Ethiopia

Article References: Jiru, B. T., & Emiru, A. Y. (2026). Prevalence of Coccidiosis and Its Associated Risk Factors Among Calves in and Around Haramaya Town, Eastern Hararge, Oromia, Ethiopia. Veterinary Medicine and Science, 12(5), Article e71245. https://doi.org/10.1002/vms3.71245

Image Credits: AI Generated

DOI: 10.1002/vms3.71245

Keywords: coccidiosis, Eimeria, calves, Ethiopia, livestock, parasitology, farm hygiene, veterinary epidemiology, dairy cattle, cross-sectional study, oocysts, body condition