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  • Kendra R. Shatswell

External Parasites in Goats - Lice

Chewing Lice

According to Merck Vet Manual, goats are susceptible to three species of chewing lice: Damalinia caprae or the common goat louse, D. limbata also known as the Angora goat biting louse, and D. crassipes the hairy goat louse (1). As their names suggest, the latter two usually favor long hair animals. Chewing lice feed on skin, keratin found in hair, and skin secretions (2,3). They are typically species specific, but sheep and goats might share types of lice; some sources indicate that, while the lice may feed on their unusual host, they might not reproduce.


Chewing lice have a flat body and wide head and are yellowish brown, sometimes with noticeably darker stripes along the body. Nymphs (immature lice) are yellow and look similar but smaller, often described as “grains of sand.” Females lay eggs called nits; these white specks are found on hair shafts, usually close to the animal’s body (5).


Sucking Lice

The linognathus species africanus and stenopsis are the main species of sucking lice to affect goats. Linognathusafricanus, or the African blue louse, as its name suggests, originated in Africa but has spread to the United States and other parts of the world. “L. stenopsis or the goat sucking louse is found in temperate regions worldwide” according to the NC State Extension website (5). Sucking lice have more oval-shaped bodies and pointed heads compared to chewing lice. Their mouthparts pierce the skin, allowing the lice to feed on blood (6). Abdomens are usually a blueish gray color and heads and legs appear orange or red. Abdomens will be blood-filled. As with chewing lice, female sucking lice lay white nits on the hair shafts of the host animal. Nymphs look identical to adults, only smaller (4).


Life Cycle

Lice are quite susceptible to temperature and even sunlight, making them more of an issue in the cool months rather than summer. Humidity is also a factor, with optimal relative humidity falling between 50-90% and anything over 90% causing a population decline in D. caprae chewing lice (7). Nits of d. caprae hatch best at a temperature of 86 degrees Fahrenheit (7). Remember that the nits are close to the goat, where they will be warmer. Depending on which source read, a lice life cycle can complete in 25-30 days, with eggs hatching anywhere from 7 to 14 days (5, 6, 8).


In terms of how long lice can survive off of the host, studies have varied. Nits are unlikely to hatch when removed from their host. Nymphs and adults can survive as little as a few hours to as long as a month, depending on environmental conditions. On the animal, lice move to different locations on the goat to account for temperature or humidity fluctuations or to avoid sunlight. In this manner, a few lice may escape notice and survive unfavorable conditions long enough to eventually repopulate in favorable ones. Transmission is primarily animal to animal, but lice may also hitch a ride on humans or equipment. (4, 5, 8)




Clinical Signs

Obvious symptoms are scratching and rubbing in an attempt to remove the irritants. The hair coat might be dull or patchy. Nits are secured to a hair shaft with a type of glue, and this can cause a matted appearance. Discomfort can lead to such “extreme grooming” that the animal is subject to hairballs (10). Sucking lice in great numbers can cause anemia, especially in young kids. Production loss and weight loss are also possible. Interestingly, lice can cause secondary issues as well. “Infestation with sucking lice have been shown to cause immunosuppression, while chewing lice have been shown to produce significant inflammatory response in goats” – Sheep, Goat, and Cervid Medicine by Pugh, page 234. (1, 3, 4, 8)


In the rare instance a goat is infected with the sheep foot louse, lameness is possible (9).

goat lice nits or eggs

Goats can harbor a few lice without any noticeable clinical signs, so an occasional exam is a good idea. Lice are visible to the naked eye, but a magnifying glass or even the zoom feature on a phone or camera might help. For a more precise examination of species, the producer might utilize sticky tape and a microscope. Certain coat colors might make the lice harder to see, as can thicker undercoats. Part the hair in several areas and look for either eggs or lice. Favorite locations are where they are harder to scratch off – the back, withers, and head are good places to start inspecting. Adult chewing lice might quickly hide when exposed, but sucking lice are unlikely to release and flee. Nits are often situated along the back and around the head. (3, 10)


Treatment

Possible treatments include powders, pour-ons, injectables, dips, and more. It must be first established that not all the following products will work for both types of lice. Generally speaking, injectables are effective only on sucking lice, not chewing – this is why it is important to correctly identify the type if the product you're using does not combat both types. Effective active ingredients are usually one of the various pyrethoids or avermectins. Common pyrethoids include cypermethrins, permethrins, or cyfluthrins (11).


Avermectins include ivermectins (don't forget to check out the blog post on dewormer classes here!). It is of utmost importance to note that any ivermectin is also a dewormer and so using one of these products for lice treatment will also be deworming your animals but POORLY because it is being used as either a topical or injectable, which can lead to resistant internal parasites – more on that here: https://www.wormx.info/oralmox and here https://extension.sdstate.edu/are-your-dewormers-effective-your-sheep-or-goat.


Most products will NOT kill nits so it is necessary to perform at least two treatments, administering the second in about 10-14 days to kill emerging nymphs.*

As is all too common, not many products are labeled for goats. A few that are labeled for goats are mostly permethrin products, including Python Dust, Durvet Permethrin 10%, and UltraBoss™. A few common off-label products include the cyfluthrin Cylence® applied topically for both types of lice and Dectomax® injectable used for sucking lice (or for mites – it stings significantly less than other ivermectin injectables). *Clean-Up™ II is a popular off-label product and the only product I am aware of that also kills nits; it contains both permethrin and the insect growth regulator diflubenzuron and treats both chewing and sucking lice.


Some producers have seen severe reactions using UltraBoss™ and it is true that just about any product can cause reactions in certain sensitive animals or when overdosed or misapplied. One vet suggested diluting UltraBoss™ 50:50 with mineral oil. If a reaction occurs soon, sometimes the product can be somewhat removed using Dawn dish soap and rinsing, but reactions might also take days to occur (12). According to Parasitipedia, it is a good idea to avoid applying a permethrin topical to any open wound, as this makes increases chances of a reaction (13). Cyfluthrins are more likely to be toxic when accidentally ingested but only “slightly” so, according to this fact sheet - http://www.npic.orst.edu/factsheets/cyfluthringen.html. While many products come ready to use, some are concentrated and require dilution – make sure to read the label carefully. Most products are dosed by weight, so getting an accurate weight is essential to avoid overdosing. (12)


Topicals need to be administered carefully along the topline, getting the liquid or powder as close to the skin as possible. It is advisable to transfer the product to a smaller dosing instrument, such as a syringe for liquids and a teaspoon or small disposable container, like a medicine cup or paper cup for powders, to avoid accidental overdosing. Make sure to read all cautions and how-tos on the labels - most will recommend the producer wear personal protective equipment such as gloves. In very young kids, lice/flea combs might be preferred over drugs, but must be used for several weeks over the kids’ entire body. Adults in contact with the kids would need to be treated as well to prevent reinfection.


Below is a bottle baby being combed for lice. She harbored just a few sucking lice when we brought her home - very easy to miss because of her coat color - and a few quickly became many. Since she was so young and in the house without other goats, I opted for a lice comb, combing every single inch of her. I did this at least twice a day for a few weeks. Always on the sink so the lice could be rinsed off the hard surface. Not feasible in every situation, but it worked wonderfully in this one - she grew to love the combing, too.

Clipping the animal when the season/weather allows will remove nits and subject the lice to both heat and sunlight. It will also make treatment more effective since it will be easier to achieve skin contact. Remember to clean your equipment and keep the clipped hair away from other goats to prevent possible transfer.


Alternative Treatments

Many folks will attempt to use a more “natural” treatment such as essential oils or DE (diatomaceous earth, a common fossil shell flour). There are a few formal studies indicating some oils and plants might be useful against external parasites – interestingly, the poisonous Jimsonweed was one (15) – but overall, effectiveness is either not proven or variable. “More extensive field trials, the standardization of good experimental design, mammalian toxicology profiling and excipient development, as well as further investigation into the residual activities and shelf-lives of oils are all required to allow the full realization of their [ essential oils] potential” – “The Use of Essential Oils in Veterinary Ectoparasite Control: A Review” (16). The aforementioned source has a long list of plants studied in the review, for those interested. The few studies on DE have shown varying reactions in lab animals – the main concern is mild lung irritation or nasal/eye irritation (17, 18) and some studies that indicate DE is effective in controlling external parasites in birds but I could not find any studies on controlling external parasites in livestock other than poultry.


Final Thoughts Lice are typically less of a health issue than internal parasites, but still warrant treatment. Goats can be infected by both chewing and sucking lice or one or the other. Infections might be worse in the winter but goats can harbor lice year around. Kids, old and ill/stressed goats can be particularly susceptible. There are many options for treatment but the producer needs to consider type of lice, possible reactions, whether tor not the product is also an anthelmentic, and work with a veterinarian if using an off-label product.


Sources

1. https://www.merckvetmanual.com/integumentary-system/lice/lice-in-sheep-and-goats

2. https://www.ncvetp.org/arthropods/category/lice

3. https://extension.wsu.edu/animalag/content/do-you-have-lousy-animals/

4. https://extension.okstate.edu/fact-sheets/external-parasites-of-goats

5. https://content.ces.ncsu.edu/lice-what-they-are-and-how-to-control-them

6. https://www.goatbiology.com/lice.html

7. http://ajesjournal.com/PDFs/2021_2/paper-5.pdf

8. Pugh, D. G., and D. G. (David G.) Pugh. Sheep, Goat, and Cervid Medicine. Third edition. Edinburgh: Elsevier, 2021. Print.

9. https://parasitipedia.net/index.php?option=com_content&view=article&id=2403&Itemid=2666

10. https://news.okstate.edu/articles/communications/2019/treating-lice-a-wintertime-threat.html

11. https://apps.msuextension.org/montguide/guide.html?sku=MT201002AG

12. Goat Vet Corner™ - Only Veterinarians Comment Facebook Group

13. https://parasitipedia.net/index.php?option=com_content&view=article&id=2676&Itemid=3018

14. https://www.sheepandgoat.com/de

15. https://pdfs.semanticscholar.org/8bbe/0d51670c5e4b6708cb3b74cc42ce78526df8.pdf

16. https://resjournals.onlinelibrary.wiley.com/doi/full/10.1111/mve.12033

17. http://npic.orst.edu/factsheets/degen.html

18. https://youtu.be/AY-yZiPFkKQ


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