External Parasites Treatment For Reptiles: Pyrethrins And Permethrins
The important external parasites in reptiles are mites, ticks, biting flies, and, to a much lesser degree, leeches. Although many reptile keepers view these external parasites as just a nuisance or an inconvenience, the truth is that they can cause or contribute to very serious pathology. To keep reptiles in captivity and not treat, prevent, and control these pests is foolhardy. The drugs and insecticides used for mites and ticks include ivermectin, dichlorvos (No-Pest) strips, and various pyrethrins and permethrins. The treatments for fly strike (myiasis) and infestation with leeches will also be presented.
Pyrethrins is a generic term for a class of insecticidal compounds isolated from the pyrethrum flowers (Chrysanthemums). A wide variety of pyrethrin- and permethrin-based products designed for small animal medicine have been employed to treat both ticks and mites. Please note that there are numerous reported deaths associated with the use of these compounds (Kihara and Yamashita 1978, Klingenberg 1993, D. F. DeNardo 1993, pers. comm., S. Barten 1994, pers. comm., R. Mauldin 1995, pers. comm., T. Boyer 1995, pers. comm.).
Pyrethrins were designed to kill cold-blooded animals (Gordon 1993). In fact, pyrethrins kill reptiles so well that a pyrethrin-based product was tested as a means of killing the brown tree snakes of Guam, which aren’t particularly easy reptiles to kill (R. Mauldin 1995, pers. comm.). Other uses for pyrethrins discussed as a killing agent for snakes were on the wolf snake (Lycodon capucinus) on Christmas Island and for copperheads (Agkistrodon contortrix) in the eastern United States. Although not extremely toxic to birds and mammals, pyrethrins were found to be lethal to reptiles in very low doses.
Some reptile veterinarians favor the pyrethrin-permethrin group of insecticides as their drug of choice for ectoparasites, perhaps because of the versatility and safety of these compounds in mammals. This is somewhat puzzling to the author; many studies exist that reinforce how toxic these products can be in reptiles. One researcher, Kihara in 1978, used Oshima lizards (Eumeces oshimaen-cis) as subjects to test the toxicity of various insecticides, focusing on the pyrethrins. The main purpose of the study was to find an insecticide that could be used to control the Habu snake (Trimeresurus flavoiridis). The study found that extremely low doses of pyrethrins were toxic (fatal) in both Oshima lizards and Habu snakes.
Because of the aforementioned toxicity, pyrethrins should be handled very carefully in reptiles. Does that mean we can’t use them at all? No, it means that we should use the attenuated (less toxic) forms of this group and use them very carefully.
Pyrethroids (which include the permethrins) are one such attenuated form of pyrethrin. If one is determined to use pyrethrins on reptiles, the pyrethroids form is preferable. The key to using this group of insecticides in reptiles is to avoid spraying if possible, allow for adequate ventilation, and limit the dosage used.
The mechanism of toxicity of pyrethrins in reptiles appears to be primarily due to CNS lesions. Although dermal contact is sufficient to cause lethal reactions, acute, or sudden (less than one minute), respiratory failure has been noted with the use of pyrethrin sprays in the absence of adequate ventilation. Acute respiratory distress, open-mouth breathing, seizures, and death were common sequelae from the application of a pyrethrin to snakes that were enclosed in sweater box–type cages (DeNardo 1993). Most deaths have been associated with a rapid inhalation route of delivery. Subsequent convulsions are indicative of CNS involvement. Although the synergists (including piperonyl butoxide and n-octyl bicycloheptene dicarboximide) in the spray products may play a role in the overall speed of the toxic reaction, toxic reactions are also seen without them. There is no specific antidote for pyrethrin toxicity other than removal of the offending product (either dermal cleaning or ventilating) and aggressive supportive care as indicated.
Mader and Palazzolo(1993) advocate the use of a permethrin for treating mites in reptiles. They instruct that the mite-infested reptile be completely saturated with the spray from the tip of the nose to the end of the tail, being careful not to get the spray into the animal’s mouth. They further suggest holding the animal under gently running tepid water to rinse off the spray as soon as it is applied. They feel that this limited exposure is adequate to kill the mites but isn’t left in place long enough to be absorbed systemically and cause toxicity. In smaller animals, they dilute the spray to water 1:2. Because of the very high toxicity of these compounds being inhaled, the authors suggest spraying them on a cloth and then applying them topically on the reptile, once every seven to ten days, as needed. Rinse off immediately. Avoid spraying near the reptile to avoid inadvertent inhalation, and use only if good ventilation is available.
These products are excellent for residual treatment of mites in the environment, outside of the cages. Again, great caution should be exercised to not create aerosols that can be inhaled by the reptiles in the cages. Specific products mentioned by Mader and Palazzolo include Durakyl, which contains 0.35 percent resmethrin and no pyrethrins, or Mite and Lice Bird Spray (8 in 1 products), which contains 0.03 percent pyrethrins.
Provent-a-Mite is a safe and effective acaricide (insecticide specifically designed to kill mites and ticks) that helps control the problem of imported ticks on tortoises and other reptiles (Burridge 2000, 2001). It is a permethrin specifically manufactured for reptiles. This product was tested on African spurred tortoises (Geochelone sulcata), rosy boas (Lichanura trivirgata), and green iguanas (Iguana iguana) using ten times the recommended dosage every fifth day for six applications. No ill effects were noted. The permethrin is applied by spraying directly onto the animal from a distance of a few inches, using a one-second burst of spray onto each leg opening and two one-second sprays for larger tortoises. For snakes and lizards, remove the animals from their containers, and spray the permethrin from a distance of 12 to 15 inches (30.5 to 38.1 cm) directly onto the substrate at the rate of one-second burst per each square foot (929 square cm). Return the snakes and lizards to the treated container only after the spray has completely dried and the vapors have dissipated.
In conclusion, pyrethrins and pyrethroids can be used in reptiles if the following precautions are observed:
- Use pyrethroids, rather than pyrethrins. If pyrethrins are to be used, make sure the concentration is less than 0.09 percent. If the pyrethrin concentration is greater than this, dilute the product with tap water. If diluting, shake well prior to using, as not all products are water soluble.
- Avoid spraying whenever practical. The inhalation of these compounds is responsible for the majority of peracute, fatal reactions. It is advised to spray the product on a cloth away from the reptile, and then apply it.
- Ventilation is essential with any of these products. Do not use these products in an enclosed cage. Do not return animals to treated cages until the cages are thoroughly dried and no vapors persist.
- Obtain your pyrethroid product from your reptile veterinarian, or base the purchase on your veterinarian’s recommendation. Treat your reptiles during the day so in the event of an adverse reaction (seizures, open-mouth breathing, altered locomotion), you can take the affected reptile to your veterinarian. Although there are no specific antidotes for pyrethrins, intensive supportive care measures may save the reptile.
Excerpt from the book Understanding Reptile Parasites by Roger Klingenberg with permission from its publisher, Advanced Vivarium Systems, an imprint of BowTie Press. Purchase Understanding Reptile Parasites here.