This article is part of a series of informative animal health articles. The series goes hand in hand with the #VideoVet video series – watch the video below.

If internal parasites in your livestock go unchecked, they can potentially cause severe economic losses. To limit production losses, an integrated parasite control plan, backed by a visual summary of each pasture or camp, is necessary.

It is crucial to identify the specific worm species prevalent on a farm. A good time to do so is just before the rain season, as many parasites will find a host prior to winter and survive the winter inside the host while conditions outside are unfavourable. The parasite’s life cycle will recommence at the start of the rain season. The three most important culprits in this regard are liver fluke, wireworm and nasal bots.

Liver fluke

This parasite requires wet, moderate to hot weather to complete its life cycle. Liver flukes will spend the dry, cold winter months in the bile ducts of their hosts. To prevent an enclosure from being contaminated by liver fluke eggs during late spring and summer, it is vital to administer parasite control treatments during late winter to eradicate the adult liver fluke population.


Wireworm is a serious problem in summer rainfall areas. This bloodsucking parasite is found in the abomasum of cattle and sheep, and causes anaemia. Wet, warm weather with temperatures above 17°C and more than 15mm rainfall per month, are ideal for wireworm development.

During unfavourable conditions, wireworm will hide in the intestinal wall of the host animal. As soon as favourable conditions return, the worm will crawl out, progress to an adult state and start laying eggs, thus contaminating the grazing.

Nasal bots

The female nasal bot fly lays her eggs in the nostrils of the host animal during summer or early autumn. The larvae quickly crawl towards the sinus cavities where they attach themselves and feed on the mucous. They will remain there throughout winter and will crawl back to the nostrils, fully developed, at the start of spring.

When the host animal sneezes, the pupae will fall to the ground, allowing the fly to emerge.


Identifying the presence of internal parasites can be done by checking clinical signs, anaemia (using the FAMACHA system) and body condition score.

Control of parasites

To effectively control internal parasites, the worm’s life cycle must be understood and intermediate hosts, such as grass mites and snails, must be considered. In addition, you need to know what the active ingredients are in the remedies you will be using.

Treatments for internal parasites

Oral dosing remedies: Ex-a-Lint Super: Reg. nr. G4369 (Act 36/1947) – contains: praziquantel 2,5 % m/v; Nem-A-Rid® Orange: Reg. nr. G4370 (Act 36/1947) – contains: albendazole 1,9 % m/v and closantel 3,0 % m/v; Fluxacur NF: Reg. nr. G3202 (Act 36/1947)/ Namibia reg. nr. V03/18.1.8/679 – contains: abamectin 0,2 % m/v and triclabendazole 10 % m/v.

Injectables: Ivotan® Super: Reg. nr. G4368 (Act 36/1947) – contains: ivermectin 1,0 % m/v and clorsulon 10,0 % m/v; Solution® 3,5%: Reg. nr. G3689 (Act 36/1947)/Namibia reg. nr. V06/18.1.2/651 NS0 – contains: ivermectin* 2,25 % m/v, abamectin* 1,25 % m/v (*macrocyclic lactone).

Easily applied pour-on products for cattle: Avotan® Pour-On: Reg. nr. G3745 (Act 36/1947)/Namibia reg. nr. V07/18.1.2/376 NS0 – contains: abamectin 5 mg/ml; Avotan® Plus Pour-On: Reg. nr. G4216 (Act 36/1947) – contains: abamectin 1,0 % m/v and fluazuron 2,5 % m/v; Sovereign®: Reg. nr. G3831 (Act 36/1947)/Namibia reg. nr. V09/18.3.9/195 S0 – contains: ivermectin 15 g and triclabendazole 240 g/L.

Nem-a-Rid® Orange

Contains: Albendazole 1,9% m/v and Closantel 3,0% m/v.
Indications: A roundworm, lungworm, milk tapeworm, liver fluke and nasal bot remedy with residual protection against re-infestation of wireworm and hookworm in sheep and goats.
Dosage: 2 mℓ/10 kg body mass.
Presentation: 2ℓ, 5ℓ, 10ℓ oral drench.

For full details read product insert or visit It is important to always know which active ingredient the internal parasite may be resistant to.

For more information, contact your MSD Animal Health representative or phone 011 923 9300. To watch more videos in this series, click here.