Current Deworming Recommendations
ALL opossums must receive levamisole (a broad-spectrum parasiticide) by injection, early in their hospitalization or orphan care.
1. First injection is given on admission, to opossums over 200 gms, including mothers with infants.
2. Subsequent boosters are usually given 14-21+ days later in juveniles or adults, NOT INFANTS. (NOTE: Captive/pet opossums may only require 1-2 total injections in captivity since infancy and protected from possible sources of infestation).
3. Opossums with hook or whip worms may require boosters sooner (e.g., 5-7 days after the first, others as fecals indicate, until cleared).
4. After initial series of 1-3 injections, one must be guided by behavioral or other physical signs. Fecals may still be negative.
Illness and trauma are immune suppressive: in the parasitized host, this becomes a double whammy! REGARDING MOTHERS : if the mother is not as healthy as you can help her achieve, HER INFANTS WON'T BE HEALTHY EITHER!
Theoretically, other antiparasitics, or even oral Levamisole should be effective. Reality is: they are never going to be as effective in the opossum as Levamisole by injection — this has been repeatedly proven in numerous rehabilitation facilities and in pets across the USA. Perhaps opossums "handle" these parasites in their tissues differently from dogs and cats. Or, possibly, absorption of oral drugs is incomplete for some reason. Whatever the cause: they are not adequate.
One additional advantage with Levamisole: It is well recognized to be an immune stimulant in every species in which it has been tested; we assume the same in opossums. It promotes cellular immunity via T-cell activation and augmentation of macrophage activity. This is a distinct advantage in immune compromised states (e.g., trauma at any age, exposure, immaturity in infants, etc.)
Individual patients may, of course, also require other antiparasitic agents. Some examples are Droncit for tapeworms, metronidazole for protozoa, a longer course of sulfa-trimethoprim for coccidia, and others. These however appear to be far less frequently required than does levamisole.
In March, 1996, Dr. Tom Rabb, Ph.D., the pharmacologist within Mallinckrodt, whose area of expertise includes levamisole and other antiparasitic agents, was kind enough to discuss the matter at length with me. He asked questions about opossum anatomy and physiology, with which he is not familiar. Then he explained, as follows, why what has been clinically observed for twelve years is valid:
1. Ivermectin is a broad spectrum GABA inhibitor; it acts at the parasites cellular level to cause its paralysis. Upon injection, it may not be cycled back into the intestines, thus won't kill the worm. If it is cycled, but the drug is kept from the worm sufficiently (i.e. rapid GI transit time), it won't kill. The opossum's GI transit time is faster than other species in whom this agent has shown efficacy; thus, it is logical that ivermectin will not work in opossums.
2. Fenbendazole (Panacur), a broad spectrum benzimidazole (oral), acts by inhibiting muscle cellular enzyme activity in the worm and causes paralysis. It must be in constant contact with the worm, over 3-4 consecutive days, to kill it. If the active metabolite is rapidly excreted, or if there is rapid GI transit (as in the opossum!), it has little or no effect. To maintain constant and adequate parasiticide levels, one risks toxicity in the opossum.
3. Levamisole (Levasole) is also a broad spectrum benzimidazole (injectable). It acts as a contact poison, which blocks nerve transmission to kill the parasite. It is unaffected by GI transit (unless one mistakenly gives it orally)...Please note that there is no advantage to exceeding the recommended dosage.
Conclusion: According to both twelve years of clinical research evidence and the knowledge and expertise of the manufacturer's pharmacologist: Levamisole is the broad spectrum parasiticide of choice in Didelphid opossums, for ascarids, whipworms, hookworms, strongyles, strongyloids, lungworms, etc.
**Pyrantel (Nemex) has not been included in this discussion due to its lesser spectrum of action than the above agents.
A Possible Urinary Tract Inflammation Syndrome
Opossums, within 24 hrs of receiving their 2nd or later levamisole injection, may develop signs of lower urinary tract inflammation/infection ("LUTI") – incidence 15-25%. Signs may include: visible perineal erythema with or without edema, genitourinary papilla ("GUP") protrusion, and frequency and/or dysuria with associated hyperactivity. On examination, the urine usually appears normal, at least initially. The syndrome can occur in either gender, at any age.
Proposed Theory: Presence of parasites in the intestinal tract is known to cause local physical damage to the mucosal lining, varying from mild to severe. Dying parasites, from certain anti-parasitic drugs, are known to cause further acute irritation, which may permit fecal bacteria to cross into region lymphatics and/or capillaries. From there, they, secondarily, may cause generalized inflammation in pelvic and perineal tissues.Pros and Cons for this Theory:
Call to Veterinarians: If you have observed this, or related, syndromes, please let N.O.S. know of your assessment of the problem. Responses will be printed in future issues.
Effective Prophylaxis: Concurrent with administration of a second, or later, levamisole injection:
Give: Sulfa-trimethoprim PO for 3-5 days. Follow medication list for dosage. Be certain to INCREASE FLUID INTAKE by giving dilute, sweetened juice. This will increase urine output, a desirable result while on this drug. This protocol appears to effectively prevent the syndrome.
Marsupials seem to handle their parasites differently than dogs, cats, and other mammals. Evidence of parasites rarely shows up in fecals of orphans, yet we know they probably contract roundworms from their mother's milk, just as do puppies and kittens. Even adults with clinical evidence for parasites (repetitive retching and regurgitation, inappropriate chewing or aggression, pacing or hyperactivity, exaggerated fear/threat response, loose, soft, or segmented BMs, pallor) occasionally test negative for parasites.
Dose your orphans once before release (at about 1.5 to 2 lbs.) with injectable levamisole- 0.02cc/lb. (This is not a misprint- they get a very tiny amount) (Veterinary Advisor's note: dilute a small volume of the stock solution; this allows one to give a more accurate dosage) They may experience vomiting for about 20 minutes, but it will pass.
For those who worry about releasing opossums without their full "God-given compliment of parasites," please rest assured that they will get their parasites back in short order. Not only will they pick them up from the foods they eat, but their own encysted parasites will be hatching out. Pre-release deworming will give them the best chance of overcoming the rigors of the first weeks of release without the added burden of parasites. By the time the worms are back in full force, your orphans will be ready for them. Hopefully, they will have become adjusted to coping in the wild, will be finding and eating all the right foods, will be stronger from all their exercise. Being hardy and more mature by then, the parasites won't be such a drag on their systems.
Use the injectable form only. If you cannot locate it, please contact us.
ALL infants receive levamisole at a time appropriate to their size and clinical status:
Where Did All the Levamisole Go?
Levamisole- 136.5 mg/ml
ACTIONS AND INDICATIONS:
Effective against many intestinal, lung, or stomach worms, etc.Also Note:
PRECAUTIONS AND ADVERSE EFFECTS:
-Occasionally causes temporary diarrhea and/or anorexia.
-Extremely high doses can lead to neuro-muscular or hepatic toxic effects, but unlikely to cause at recommended dose/frequency.
DOSE, FREQUENCY, ETC.
SQ 0.02ml (2.75mg)/lb
May repeat in 14-30 days. Sooner for hookworms, etc.
NOTE: For animals under 3 lbs, must dilute the stock solution before administration, for accuracy (choose a concentration convenient for the size of patient). The usual (deworming) dose of Levamisole (13.65% or 136.5 mg/ml) for opossums is 0.02 ml/lb (2.75mg/lb). Because the amount is so small, one must dilute the stock solution for accuracy in opossums under 3 lbs. To do this, draw up 0.1 ml of 13.65% levamisole in a 1 ml (TB) syringe, then draw to the 0.5 ml mark with distilled or sterile water. Mix in the syringe by tapping. Administer 0.1 ml/lb of this dilution (27.3 mg/ml=2.73 mg/0.1ml) subcutaneously.
National Opossum Society
P. O. Box 21197
Catonsville, MD 21228