A Wildlife Rehabilitator’s Guide To Parasite Control

Ron Hines DVM PhD

The products and techniques mentioned on this webpage are all “off-label” product techniques and uses. That means that they are not government or manufacturer-approved uses or techniques. In the United States, no medications are approved to treat wildlife. The profits they would bring to the manufacturers do not justify the research and expenses that would be involved to gain government approval. I make my decisions based on my experience and the experience of others in caring for wildlife. But you must make your own independent, knowledge-based, decisions when you consider using any product off-label in or on animals for which they are not government-approved.

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Sevin® & Generic Brands of 5% Carbaryl

Carbaryl is an agricultural insecticide that has been available since 1958. A major ecological advantage of this compound is that it breaks down rapidly in the environment. For many years, carbaryl was a standard treatment for human head lice. However over time, human lice became resistant to it. Carbaryl is of low toxicity to birds and mammals. Scientists measure toxicity in a measurement called LD50. Applied to the skin of rats even 5000 mg/kg had an LD50 of zero. I mix 5% garden carbaryl powder with an equal amount of corn starch to obtain a 2.5% carbaryl mixture. A single light powering with that mixture eliminates chewing lice on pelicans, sea birds and raptors. It is equally effective in eliminating mites on wild songbirds (passerine birds). The ones I see that are most likely to need it are starlings. I apply a small amount of the dry corn starch-diluted powder mixture with a dedicated salt shaker that is clearly marked 2.5% CARBARYL. The half-life of topical carbaryl on birds is about 16 days. Sunlight enhances carbaryl breakdown as do humidity or water. But I hesitates to suggest that you do what I do without an effective mask and gloves because powders of all kinds are easily inhaled. I don’t want you to be needlessly exposed to chemicals.

The Naturalyte® Conserve Spinosad 0.5% Alternative To Carbaryl

Spinosad is sold under various manufacturer names. It is best known to dog and cat owners because it is the active ingredient in Elanco’s Comfortis® chewable tablets sold for the control of fleas and Triflexis® in which the Company combines spinosad with milbemycin so it also kills heartworms. Naturalyte® Conserve Spinosad 0.5% is not approved for animal use. It is sold as one of the very few insecticides that is USDA-approved for used by organic farmers. That is because spinosad is a natural product derived from a certain bacteria. Spinosad is quite effective in ridding poultry of mites. (read here) Here in humid tropical South Texas (a flea’s paradise) I mist spinosad on my dog as an extra precaution against fleas and kissing bugs . But I have also found that spinosad at the same concentration is effective in ridding starling chicks of mites. I add 0.5 ml of Naturalyte to 30 ml of water and then add one drop of Dawn™ dish-washing detergent. I give the birds a light misting using a 4 oz hairdresser’s spray bottle and then transfer them to new accommodations. Thirty millilitres is barely enough to activate a 4 oz mister, but enough to mist a great number of birds, bird cages and the like. After misting, I blow dry the chicks. These birds have shown no side effects. Spinosad is also effective in ridding urban opossum babies of fleas. However I continue to just pick fleas off of opossum babies with tweezers and drop them into a bottle cap of alcohol when I encounter them on immature urban opossums. Fleas that have fed on opossums have the potential to transmit typhus. (read about that here)

Pyrantel Pamoate

Pyrantel Pamoate is an effective oral worming medication that eliminates many species of larger intestinal parasites (nematodes). The drug’s safety lies in the fact that very little of the pyrantel is absorbed through the animal’s intestines. So it has few or no dangerous effects at the doses we generally give. that is why for many years pyrantel has been the standard treatment for pinworms in children. Pyrantel is also one of the active ingredient in dog heartworm medications such as Heartgard Plus®. It is added to kill intestinal roundworms and hookworms. The other active ingredient, ivermectin is what prevents heartworm disease. Pyrantel pamoate paralyzes adult intestinal nematode parasites. So the worms pass out of the animal’s body in its stool. The standard dose of pyrantel pamoate is 2.5 to 5 milligram/pound (5-10 mg/kg) with smaller animals receiving the upper end of the dose range. It is wise to repeat the dose twice at weekly intervals. That is because many parasites have early development stages that reside in other locations in the body where pyrantel pamoate can not reach them. The second and third dose is for those stragglers. (read here) An accepted dose of pyrantel pamoate in birds is 4.5 mg/kg (~ 2 mg/lb) repeated in 10-14 days. But others suggest a dose up to 25 mg/kg repeated in 14 days. I see no need to go that high. For domestic rabbits, 5-10 mg/kg (~2.5-4.5 mg/lb) shortly after eating and repeated 2-3 weeks later is an accepted dose. For reptiles, an accepted dose is 5 mg/kg repeated two weeks later.

Drontal Plus® consists of pyrantel pamoate combined with praziquantel, and febantel, a compound that converts in the body to fenbendazole. I have no experience giving it to wildlife. The drug is quite safe when given to dogs. The third ingredient in Drontal Plus®, febantel, metabolizes in the body to fenbendazole . For it’s intended use in dogs, febantel increases its effectiveness against whipworms as well as many other species of parasites that inhabit the canine intestinal tract. Some say that Drontal Plus is not safe to give to porcupines and groundhogs. I do not know if that is true. A problem with giving very broad-spectrum wormers to wildlife that rely on beneficial organisms that inhabit their cecums is that these drugs also kill some of the “good” cecal organisms that those species rely on for digestion and vitamin production. If those questionable products are given, it is best to re-inoculate (an oral dose of bacteria) the animal soon after with bacteria from the stool of healthy members of the same species.

I routinely give pyrantel pamoate to pelicans and raccoons at the same dose suggested on the label for dogs. When I feel that pyrantel pamoate has not be effective enough against all the intestinal parasites that I worry that a wild animal might have, I give mammals and birds ivermectin and/or metronidazole. My last choice is fenbendazole paste. I discuss each of them below:

Fenbendazole

Fenbendazole is a very effective worming compound for wildlife. You can purchase it as a liquid or as a paste. The traditional brand name of fenbendazole is Panacur®. Fenbendazole kills considerably more species of intestinal parasites than pyrantel pamoate. The febantel portion of Droncit Plus® is converted in the animal’s body to fenbendazole. All suggested wildlife doses are a guess. They range from 5 to 50 mg/kg (~2.5-25 mg/lb) with a second and often a third dose given at weekly intervals. As for many drugs, the lowest doses on a per pound basis are reserved for very heavy animals such as bears (the more an animal weight, the less per pound dose is required). The higher doses are reserved for light weight species. Small mammals and all birds tend to eliminate drugs from their bodies faster because they usually have higher metabolic rates.

I always administer fenbendazole at a lower-than-suggested dose to wildlife – and even then with caution. I believing that it is safer to give a very low drug dose multiple times than to give a higher dose only once or twice. Fenbendazole effectively kills some blood parasites (microfilaria) and giardia as well. But there are reports that fenbendazole has caused feather deformities in fledgling birds. Small finch-like birds are particularly susceptible to fenbendazole toxicity. Fenbendazole toxicity was also suspected to have caused the deaths of vultures, storks, pigeons, doves, porcupines, rabbits and cormorants. However cause and effect were never sufficiently proven.

Ivermectin

Ivermectin is commonly sold as a 1% solution. That is the same as 10 milligrams per millilitre (ml) or per cubic centimeter (cc). The 1% solution also equals 10000 micrograms per millilitre. The standard veterinary dose of ivermectin – both by injection and orally – is 200 micrograms/kilogram (0.18mg/pound). There is much less ivermectin on a per pound/kilogram tablet given to dogs to prevent heartworms. Pills like Heartgard® contain 6 micrograms/kg (2.72 mcg/lb ) of ivermectin. Your dog only need that low a dose because you are giving it monthly as a preventative to kill heartworm microfilaria before they can mature into adult heartworms – not as a cure. Double the standard 200 mcg/kg amount can be neurotoxic to birds. Doses above about 2500 mcg/kg (2.5 mg/kg) are toxic to cats and even very small amounts of ivermectin and its cousin compounds can be toxic to reptiles.

If you are treating non-domestic cats, I would stay below the domestic cat dose, or better still , use a different product. Ivermectin appears to be safer when it is given orally rather than by injection. Ivermectin can be safely diluted with propylene glycol (not ethylene glycol). There are those that believe that some brands (Eqvalan®) can be safely diluted with water. I never have done so, but I believe that it is the time interval between diluting ivermectin and administering it that is probably more important. Ivermectin is effective in killing many species of mites, gapeworms and some intestinal nematodes. Ivermectin is highly toxic to fish and crustaceans. My biggest use of ivermectin is to rid pelicans of “bag lice“. I inject the proper 200 mcg/Kg dose for the bird’s weight into a fish and toss one to each bird. We did the same “toss” procedure to the sea lions at SeaWorld. I have also given ivermectin orally ( at the dog monthly per pound/Kg dose) to otters, raccoons. I have never encountered toxicity problems. As I previously mentioned, ivermectin can be fatal to turtles, tortoises, other reptiles and cats.

Metronidazole

Metronidazole was first marketed for humans as Flagyl®. The drug kills protozoa, microscopic one-celled organisms. It kills a few bacteria too (anaerobes), but none that are typically a problem in wildlife rehabilitation settings. Metronidazole also appears to have positive effects in animals with diarrhea even when the cause of the diarrhea is not due to an organism the drug is known to destroy. ( read here ) Veterinarians do not know why. The two most common reasons that wildlife rehabilitators give their animals metronidazole is to treat trichomonas disease in birds and diarrhea in raccoons. The drug has no effect on virus.

The metronidazole dose in most wildlife is between 15-25 mg/kg (~7-11 mg/lb) given once or more commonly twice a day. Metronidazole tastes horrible. If you must stress and struggle with an animal to administer the dose, a once-a-day dose at the high end of the dose range is probably advisable. The required treatment period ranges from 3-7 days depending on response (which is usually no more diarrhea). When treating thrush or trichomoniasis in birds, some suggest 10-30 mg/kg orally twice a day for five to ten days. There is a warning that small “finch”-type birds do not handle metronidazole well. A group with extensive experience administering metronidazole to raptors gives their patients metronidazole at up to 100 mg/kg per day orally for 3 days. At the Bush Gardens rehab center in Florida, metronidazole is given orally to raptors at 50 mg/kg, once a day. You can see that there is no agreement as to what a proper dose of metronidazole should be or how long it should be given. ask me for Samour2003pdf & Spriggs2020

Diarrhea can be a major problem when raising large numbers of orphan raccoons. When it is, the most common causes are over-feeding milk formulas rather than more frequent smaller feeding, the parvovirus of dogs or raccoons, and canine distemper. Metronidazole has no effect on parvovirus or distemper virus. When metronidazole seems helpful to those raccoons, it is either because the parvovirus or distemper virus has immunosuppressed them causing an overgrowth of protozoa such as giardia and/or unhealthy bacteria or because of metronidazole’s unexplained “calming” effect on the intestinal tract no mater what the underlying cause seems to be. The usual dose in raccoons is the same as the one for dogs and cats, 5-20 mg/kg divided into a morning and evening portion for about 5 days. Some raccoon rehabbers give considerably higher doses. As with birds, there is little agreement as to what a proper dose of metronidazole should be. You need to combine that with the same treatments provided to parvo-infected dogs. ( read here ) Young ambassador raccoons need a series of Merial/Boehringer Ingelheim’s Recombitek C3/C4 or Merck’s Nobivac’s Canine 1-DAPPv and an Emrab-3 rabies shot at 16 wks (if that is legal to do in your state).

Trichomoniasis (some call it trichomonosis) is most often seen in doves, pigeons and the raptors that prey upon them – particularly cooper’s hawks. Birds near large urban centers seem particularly susceptible – probably because of the presence of large flocks of infected urban pigeons and the abundance of bird feeders and bird baths that draw abnormally large congregations of birds together for cross-infection. Falconers call trichomoniasis “Frounce”. Because the disease has plagued their raptors for centuries, it is traditional for them to remove the heads of pigeons and doves before they offer them to their raptors to eat. I am uncertain if there is any benefit to doing that because trichomonads are not confined to the bird’s head. But perhaps it is helpful. Typical signs you might see in infected doves, pigeons and raptors are whitish yellow, slightly raised spots in the mouth (plaques, canker) with a consistency of cheese, gaping (open mouth), gasping, refusal to eat, slow crop emptying, and vomiting (regurgitation). The only way to make a definite diagnosis is to see the wiggling organisms under a microscope.

Candida (“sour crop” or thrush ) fungus, aspergillosis (another fungus) or a vitamin A deficiency can all be mistaken for trichomoniasis. Since all of these diseases occur in birds under stress, several of these organisms can be present at the same time. Metronidazole is only likely to be beneficial when trichomonas or some other protozoa is one of the participants.

Another cause of trichomonas overgrowth in birds and mammals is giving antibiotics and/or corticosteroids to animals that did not require them. Antibiotics alter the normal bacteria balance in all animals and corticosteroids lower resistance to infectious disease. Metronidazole is not helpful when treating Candida. Candida needs to be treated with an anti-fungal medication such as nystatin, itraconazole or fluconazole. Aspergillus fungus is never successfully treated – at least not by me. There is also some evidence that dilute boric acid is helpful in killing trichomonads. It has been found that young raptor nestlings – the most susceptible to trichomonas disease – have a less acidic mouth than older nestlings or adults. ( read here ) topical boric acid helps cure human trichomonas disease ( read here ) ; but I do not know of it having been tried in birds. If you do let me know.

There are other alternatives to metronidazole. One is carnidazole (Spartrix®) and the other is ronidazole (Ronex®). I have no experience using either of them, but one published dose for carnidazole in raptors was 30 mg/kg given once orally. Another suggested the same dose once a day for 2-3 days. Both are marketed for pigeons and for the raptors of falconers. Since I know of no reports of trichomonas having become resistant to metronidazole, the only advantage of these newer and more expensive products might be a more pleasant taste. Metronidazole is exceedingly bitter and metallic in taste. Chewy and and Wedgewood sells flavored metronidazole in liquid form. But neither of their pharmacists could tell me which of their flavors, if any, might be most acceptable to birds or raccoons.

Doramectin

Doramectin, marketed as Dectomax®, is an injectable medication approved for use in cattle and swine to destroy a large number of intestinal and superficial (skin) parasites. Doramectin is in the same class of compounds as ivermectin (an avermectin) and marketed in the same 1% solution concentration as ivermectin. Its suggested dose in cattle and pigs, 200 micrograms/kilogram, is the same as the ivermectin dose. There are reports are that doramectin, given to rabbits “off label” at 200 and 400 micrograms/Kg. subcutaneously every three days successfully cured them of ear mites and scabies mites. It is also effectively used “off label” in dogs at 0.6 mg/kg (600 mcg/kg) once or twice weekly to cure them of demodectic mange.

I became interested in doramectin because I read that it was effective in curing baylisascaris-positive pandas and I thought it might be of value in ridding raccoons of Baylisascaris procyonis and skunks of Baylisascaris colomnaris . Both are potential health hazard to wildlife rehabilitators and the general public. Nothing, short of a blowtorch, destroys baylisascaris eggs. I had planned to give doramectin orally along with pyrantel pamoate – if and when I found characteristic nematode eggs in raccoon or skunk stool. However I rarely accept baby or injured urban raccoons anymore. That is because I know of no acceptable places to release them. If an area in South Texas has acceptable food sources for raccoons, it already has raccoons there at its maximum capacity. So adding more raccoons simply means that the new one or a resident raccoon must eventually perish from starvation. Feeding stations simply increase the raccoon population density to a point where a plague such as canine distemper or parvovirus spreads through the colony and decimates it. In urban settings, raccoons are also a common transmitter of leptospirosis . ( read here ) In recent years very few skunks have been dropped off with me here along the Mexican border. So that project too is on hold too.

When Internal Parasites Are Present Are They Always The Cause Of A Problem In The Animal I Am Caring For?

When you find a few intestinal parasites (or their eggs) in the stool of a bird or a mammal, that does not necessarily mean they are causing the animal current harm or that they are the underlying cause of its health issue. A lot of intestinal parasites live in small numbers and relative harmony with their hosts. In those situations they do little or no damage to the animals in which they dwell.

It is never in a parasite’s long term interest to make its host ill. It is only when an animal’s living conditions were/are such that the parasites over-multiplied through constant re-exposure to their eggs or larva, or when starvation, crowding or other stressors are present that the situation becomes dangerous. The photo above is from any autopsy of an adult white pelican whose car crash injuries I could not repair. As wildlife rehabilitators, we all feel better when we rid wildlife of parasitic worms. I always worm them – if only to be sure that the parasites do not proliferate out of control in my space-restrictive cages and pens. But I have never autopsied a healthy brown pelican with traumatic injuries that did not have a few of these disgusting parasites either.

You can see that the worms and the pelican in the photo appear to have been living in harmony (commensally). When there is no evidence of stomach inflammation, I believe that they are just freeloaders living off the pelican’s fish catch. When that is the case they are called symbionts. Some symbionts actually benefit their hosts. Several of the gastric nematodes of pelicans are thought to do their damage to the mullet that are the parasite’s intermediate host, not the pelican. They are thought to do that by making the fish slower and easier to for the pelican to catch – just as toxoplasma parasites make mice easier for cats to catch. ( read here ).

Coccidia

It is also quite normal for wildlife to harbor a few resident coccidia. Coccidia also tend to get out of hand when animals are confined to too small an area, when too many animals are attracted to backyard feeders or other concentrated sources of food, and in situations like floods where ground and water sanitation is poor. All those situations favor constant reinfected and a coccidia health threat. We don’t have very effective drugs to treat coccidia. Ivermectin and fenbendazole destroys most multicellular parasites (the bigger ones). But neither drug appears to kill coccidia. In fact, some have noticed a coccidia “bloom” subsequent to ivermectin treatment. The most commonly used medications to treat individual animals that have diarrhea due to coccidiosis are the the sulfa-drug group, sulfadimethoxine ( Albon®) or trimethoprim/sulfadiazine ( Tribrissen®, Equisul-SDT®). The problem is that both taste bad and both must be given for many days to be effective. The most common sulfadimethoxine dose used in birds is 25-50 mg/kg once or twice a day orally for 3-7 days. To treat coccidiosis in carnivorous mammals and ruminants, 50 mg/kg/day initially and then about half that dose for another 10 days. A similar dose has been effective in rabbits and rodents. But it takes a longer treatment time to clear them. Tribrissen has been used at 40 mg/kg twice a day in birds. In rabbits and rodents at a similar dose and at 15-30 mg/kg in other wild mammals.

A small studies using ponazuril to treat coccidiosis in baby robins at a rehab centers found it was ineffective (the drug seemed effective in limiting coccidiosis in shelter cats). The best way for you to control coccidia, protozoa and larger parasites in your wildlife rehabilitation center is through husbandry: separation, spacing out of animals into individual containers, frequent changes of the the floor bedding/substrate and no sharing of utensils or food containers.