Nematode © Christian SLAGMULDER

Anti-parasitic drugs: humans and animals united in the same fight

Ivermectin conquers a parasitic disease: bovine hypodermosis

Research carried out at INRA has contributed to eradicating hypodermosis in France. Hypodermosis is a disease caused by a parasite that infests cows. Treatment involves micro-doses that are effective in and applicable to all cattle, including lactating cows.

By Chantal Boulard and Pascale Mollier, translated by Inge Laino
Updated on 07/04/2017
Published on 12/07/2015

Warbles on cows: subcutaneous abscesses caused by the larvae of a parasitic fly, leading to hypodermosis.. © INRA, Chantal Boulard
Warbles on cows: subcutaneous abscesses caused by the larvae of a parasitic fly, leading to hypodermosis. © INRA, Chantal Boulard

Bovine hypodermosis fly.. © INRA, Chantal Boulard
Bovine hypodermosis fly. © INRA, Chantal Boulard

Bovine hypodermosis is a disease caused by non-biting flies (1) whose larvae specifically target cows. After penetrating the skin of the ruminants, the larvae migrate into deep tissue, reaching the subcutaneous dorsal tissue of the animal after ten months. They cause abscesses known as warbles. The larvae emerge and fall to the ground, where they take one month to turn into pupa, then adult flies. Their biological cycle is annual. This disease is devastating for farmers and ethically inacceptable in terms of the well-being of animals. Effects on the animals include stunted growth, immune suppression, decreased milk production, a drop in the quality of meat and leather, etc.

A disease with thick skin!

It took some sixty years to tackle bovine hypodermosis. The fight against the disease began in the 1940s, with three successive generations of insecticides: organochlorines, organophosphates, and ivermectin starting in the 1980s. “Ivermectin applied subcutaneously at a dose of 0.2mg/kg proved effective against larvae in the third stage”, recalls Chantal Boulard (2). “But treatment was prohibited in lactating cows (3). That is why recurring infestations took place every year. In 1990, there were still regions where 50% of cattle were affected by the disease”.

The development of micro-doses of ivermectin

Throughout the 1980s, research carried out at INRA explored the high susceptibility of parasites in very early larval stages to ivermectin. It was found that the drug, administered in winter subcutaneously at doses of 0.002mg/kg (i.e. a dose 100 times lower than that recommended by the drugmaker), was 100% effective against the parasite in its first larval stage. The INRA studies also showed that it was possible to use micro-doses on lactating milking cows with no health risk for milk consumers.

A nationwide treatment programme

In France, a national programme to control hypodermosis was launched in 1995 (4), using micro-doses of ivermectin on all cows. Micro-doses of the drug were applied to all bovine cattle in France (including lactating cows) once a year for three consecutive years. In 2000, the whole of France was recognised as a “warble-free zone”. With bovine hypodermosis eradicated from the country, systematic treatment was suspended and a national serological surveillance system was put in place to detect a possible resurgence of the disease.

This success story is due in part to the use of micro-doses of ivermectin. Its total effectiveness against larvae in the first stage of hypodermosis, its affordability, and the significant reduction of anti-parasitic residue found in milk, meat and the environment make ivermectin the preferred tool for this type of coordinated and time-limited collective prophylaxis.

(1) Hypoderma bovis fly and Hypoderma lineatum.

(2) Chantal Boulard: researcher in the former IASP Unit, now known as joint research unit 1282 ISP Infectiology and Public Health, 37380 INRA Nouzilly, France, boulard.chantal@orange.fr

(3) See section 7 of this report.

(4) Ministerial order published in November 1994.

Reference

Boulard C. et al. 2008. A successful, sustainable and low cost control-programme for bovine hypodermosis in France. Veterinary Parasitology, 158-1-2, 1-10.

Chronology of a success story

- 1941: Obligation to treat animals with hypodermosis with organochlorine ointments.
- 1950: Treatment with organophosphorates applied on skin (“pour-on”) or subcutaneously.
- 1980: Ivermectin available in a subcutaneous injection (0.2mg/kg). Treatment prohibited in lactating cows.
- 1995: Use of micro-doses of ivermectin (0.002mg/kg) in subcutaneous injections for all cattle, including lactating cows, within the framework of an organised prophylactic programme limited in time.
- 2000: France is declared a hypodermosis-free zone. Treatment abandoned.