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Sheep ked, nasal bots, itch mite and sheep scab

The sheep scab mite, Psoroptes ovis, has been eradicated from Australia for over a century. Source: Gerry Brennan, Queen's University Belfast
The sheep scab mite, Psoroptes ovis, has been eradicated from Australia for over a century. Source: Gerry Brennan, Queen's University Belfast

by Deborah Maxwell, ParaBoss Operations Manager

August 2015

 

Recently, in the ParaBoss technical forum, the question was raised “has anyone seen sheep ked and itch mite lately?”

It seems that last sightings were some years ago, but it has prompted me to write about four parasites that modern Australian sheep farmers no longer or rarely have to contend with: sheep ked, nasal bot fly, itch mite and sheep scab. So what are they?

Sheep Ked (Melophagus ovinus

These intriguing beasties look like a 6-legged tick because of their flattened shape, prominent abdomen and protruding legs (and have been called a sheep tick). They seem like a cross between flies and lice with a measure of barber’s pole worm thrown in! They are, in fact, a fly—about the size of a house fly—although wingless. But unlike our blowflies, ked live their entire life on the sheep in the fleece—like lice—but suck blood with their piercing mouthparts and, in heavy infestations, cause anaemia (like barber’s pole worm). The pupal cases of ked adhere to the wool and the faeces of the adults stain and downgrade the wool.

Fortunately, ked are quite sensitive to chemicals and dips, in particular rotenone and organophosphates, which has made their occurrence very rare over the last few decades. If you know of recent occurrences of ked in Australia, please let ParaBoss know.

Nasal bot fly (Oestrus ovis)

In contrast, nasal bots are the parasitic larvae of another fly, the nasal bot fly. The adult fly deposits larvae around the sheep's nostrils and from here they migrate into the nasal cavity and sinuses, taking from 6 weeks to 10 months to complete their development within the sheep. Once the larvae are mature they are sneezed out.

Fortunately, nasal bots generally cause the sheep no problems. Nasal bots are now less common as they are also controlled by the macrocyclic lactone and closantel worm drenches (MLs; ivermectin, abamectin and moxidectin; and closantel). 

Itch mite (Psorobia ovis, formerly Psorergates ovis)

This little mite is still likely to be around, but it is difficult to detect, so its prevalence is not known. They are only about 1/5 of a millimetre—too small for the naked eye. Itch mites live in the surface of the skin and cause intense irritation resulting in rubbing and scratching, which may lead to severe fleece damage.

Although reports of itch mite were common in the 1980s the introduction and use of macrocyclic lactone worm drenches (MLs; ivermectin, abamectin and moxidectin), to which they are very susceptible, has seen them—or at least their effects—decline markedly.

Sheep scab (Psoroptes ovis)

Another mite, this one causes psoroptic mange, which can occasionally affect cattle, horses and goats. The mite pierces the surface of the skin to feed on the body fluids and this causes intense irritation leading to rubbing, wool loss, bleeding and scab formation, with affected sheep losing weight. In 1865 it was reported that this disease was causing £500,000 financial loss each year to the Australian colony.

While mercurial ointment mixed with lard was an early remedy, it was the chance inclusion of tobacco into a dip (containing sulphuric acid) used to soften scabs before the ointment was applied that was found to kill the mite. This was later changed to a sulphur and lime dip.

Sheep scab was, in fact, responsible for the first Australian legislation aimed at controlling an animal disease. In NSW, legislation was first enacted in 1832, but it wasn’t until it was enforced with full-time inspectors that control was rapidly achieved—in fact, the history of the NSW Pastures Protection Boards, is closely linked. Eradication was complete in NSW, Qld and SA by 1866, but took until 1876 in Victoria, 1881 in Tasmania and 1896 in WA.

While it is not present in New Zealand, it still occurs in many other sheep producing countries, and Australia is indeed fortunate to have eradicated it so long ago—it’s a pity lice weren’t eradicated at the same time.