Garlic’s effectiveness (or not) against equine parasites in spotlight

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The worldwide problem of drug resistance in nematode (roundworm) populations in horses, leading to a growing interest in alternative methods of control.

Anthelmintics derived from plants can be an alternative for the treatment of parasitic infections, and garlic formulations are often used in prevention and treatment of intestinal parasites.

But are they effective? Two recent studies have produced conflicting evidence regarding the effect of garlic against strongyle nematodes.

Adult worms of Strongylus spp. live in the large intestine of horses and are commonly categorized as
large and small strongyles. Of the more than 100 species of internal parasites found in horses, almost half are strongyles. Strongylus spp. is frequently responsible not only for generally poor health, but
also gastrointestinal dysfunctions, including colic. Infective third-stage larvae  ingested from contaminated pasture penetrate the mucosa of the large intestine, moult to fourth-stage larvae in the submucosa. In the case of Strongylus vulgaris, they then proceed to the root of the cranial mesenteric artery along the arterioles and arteries that supply the intestine, where they may cause parasitic thrombosis and arthritis. Larvae of the other two species may be found in various parts of the body, including the liver, prerenal tissues, retroperitoneal tissues, and pancreas.

Ferula asafoetida. 
Ferula asafoetida. © Patrick Verhaeghe
Anti-parasitic effect on larvae

Mousa Tavassoli and colleagues at the Faculty of Veterinary Medicine at Urmia University in Iran conducted a study of the anti-parasitic effects of hydroalcoholic extracts of garlic (Allium sativum) and Ferula asafoetida (a plant native to the area that has been used as a spice in food and to treat intestinal parasite infections in traditional medicine).

Third-stage strongyle larvae were exposed to different concentrations of extracts of both plants and to tap water.

The researchers found that both garlic and Ferula asafoetida extracts were effective against the larvae, demonstrating dose-dependent anthelmintic activities. Larval mortality rate increased significantly as the time of exposure to the extracts increased.

They conclude that hydroalcoholic extracts of F. asafoetida and A. sativum have potential anthelmintic and larvicidal activities in vitro. They suggest that further in vivo evaluation of the different parts and fractions is needed to make use of these plants for beneficial purposes.

The researchers said it was “interesting to note that the extracts are combinations of many components and are not pure, so these primarily results only suggest the potency of these extracts. Nevertheless, our discovery that the plant extracts can be used as accessible source of natural anthelmintic from plants is rewarding, as it will lead to the development of a phytomedicine to act against parasites”.

“These extracts have enormous therapeutic potential, as they can fulfil their purpose without any side effects that are often associated with synthetic compounds.”

A garlic press with pressed garlic. © Lee Kindness [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
A garlic press with pressed garlic. © Lee Kindness [CC BY-SA 3.0], via Wikimedia Commons
No effect on strongyle egg shedding

On the other hand, a study in Italy assessed the effect of garlic on egg-shedding and found that garlic failed to control intestinal strongyles in naturally infected horses.

Francesco Buono and colleagues monitored the effect on egg shedding in horses naturally infected with intestinal strongyles.

The field trial was conducted on a trotting horse farm in Southern Italy. Fifteen naturally infected mares were allocated to one of three treatment groups:

  • fresh garlic group – animals received 40g of fresh crushed garlic once daily for 15 days;
  • dry garlic group – animals received 40g of commercial dry garlic flakes food supplement once daily for 15 days;
  • control group – no treatment

After two weeks of garlic administration, a faecal egg count reduction test showed the garlic failed to reduce strongyle egg shedding.

Long-term administration of garlic has been associated with anaemia. However, in this study, red blood cell counts remained within normal limits throughout the treatment period.

They concluded: “In our study model, the oral administration of garlic formulations has no effect on reducing the egg shedding of intestinal strongyles, and the garlic supplementation over a short period of time is not responsible for hematological changes in horses.”

The in vitro effect of Ferula asafoetida and Allium sativum extracts on Strongylus spp. Tavassoli, G. Jalilzadeh-Amin, VRB Fard, R. Esfandiarpour. Ann Parasitol. (2018) 64 p59–63.

Preliminary Observations of the Effect of Garlic on Egg Shedding in Horses Naturally Infected by Intestinal Strongyles. F.Buono, L. Pacifico, D. Piantedosi, G. Sgroi, B. Neola, C. Roncoroni, A. Genovese, D. Rufrano, V. Veneziano. Journal of Equine Veterinary Science (2019) 72, p79-83.

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