In November and December 2002, myxomatosis was confirmed via postmortem tissue pathology in rabbits living indoors in Solano County (Vallejo) and in Sonoma County (Sebastopol), respectively. On March 31, 2003, another Vallejo house rabbit presented with end-stage myxomatosis symptoms and was euthanized.

That this last Vallejo house rabbit became infected with myxomatosis so early in the spring would indicate that the disease "wintered over" in host insects and that rabbits who live outdoors or who go outside (at any time of day) are at risk of infection.

This article is an attempt to relate, from a layperson's perspective, the progression of the disease so that others who have rabbits might increase their ability to recognize its symptoms and take appropriate action. It also provides one course of action that was taken in the 2002 Vallejo and Sebastopol cases that caregivers may wish to discuss with their veterinarians should they determine that their rabbit is presenting with early myxomatosis (myxo) symptoms.

Please contact everyone whom you know with rabbits and share with them what we have learned:

1. Myxomatosis is a pox virus transmitted by any biting, bloodsucking insect. Typical vectors include mosquitoes (which have been documented to travel 40 miles), fleas (which may be carrying the virus after having bitten an infected animal and ride into your home on your pants leg or on your outdoor dog or cat), fur mites, gnats, biting flies, ticks, etc.

If your rabbit is within 40 miles of these confirmed cases and has been outside in the last three weeks or has been around any other animal that may have been outside in the last three weeks (and therefore may be carrying fleas), your rabbit is at risk.

2. Contrary to what some of us believe, mosquitoes are active throughout the day, not only at dusk and dawn. They prefer the shade, where, if your rabbit was outside to romp, he or she may have rested. The Vallejo rabbits who died from myxo were all house rabbits let outside to play only under supervision by their caregivers and only during hours when mosquitoes were thought to be inactive.

3. If you use Advantage to protect your animals from fleas and administer it on a four-week schedule, you need to know the results of Bayer's own tests regarding its efficacy. In weeks one and two following the regular Advantage dose, the fumes that cling to the surface of the animal's skin disable fleas before the flea can bite. In weeks three and four, fleas jumping onto the animal can bite at least once before becoming disabled. This means that your cat or dog (treated with Advantage) may well carry a flea into your home still capable of biting your rabbit -- and infecting him or her with myxo -- in weeks three and four. Or if your rabbit goes outside where flea-bearing animals (cats, raccoons, possums, etc.) have been, even if your rabbit is on an Advantage program, during weeks three and four, he or she is exposed to the chance of being bitten by a flea that had fed on an infected animal.

4. We theorize that the first of the 2002 Vallejo rabbits may have been initially infected via mosquito bite but that myxo was more than likely spread to the other rabbits in the home via flea bite, since their caregiver used Advantage to guard against fleas. Six house rabbits in that Vallejo case were lost to myxo during the month of November. Although the Sebastopol rabbits were housed indoors in a barn, their caregiver does not rule out mosquitoes as the initial vector in that case. The four Sebastopol rabbits whose necropsies confirmed that they died of myxo lived together and in a separate space from the surviving nine rabbits in that household.

5. Conventional wisdom holds that the symptoms of myxomatosis are extremely elevated body temp -- 106° F (Fahrenheit) or 41.1° C (Centigrade); puffy, swollen face; lesions on nose and/or around genitals; deeply inflamed, swollen eyelids, nostrils, lips, genitals, anus, and ears. Sadly, I will hereby go on record with my direct observation of the confirmed myxo rabbits in the 2002 Vallejo case and say that those symptoms occurred at end stage. Additionally, not all the rabbits whose tissues tested positive for the pox virus came down with all -- or any -- of the end-stage symptoms above.

6. Here, in approximate sequence and placed over a period of two weeks, are all the symptoms I personally have observed in rabbits who eventually presented with some or all of the end-stage symptoms, died, and on whose tissue the lab work came back positive for the pox virus:

Earliest

• Lethargy; more sleep than usual; less playful.

• Reluctance to follow usual schedule.

• Slight elevation in temp, i.e., 104° F or 40° C (103° F or 39.4° C is considered the high end of the normal range for rabbits).

• Increased interest in water.

• Decreased interest in food except for favorites; significant drop in amount eaten, even with those items added.

4-6 Days

• Resumes near-normal activity level.

• Interest in food increases. May eat more than usual. May eat in pronounced "stages," leaving the vegetables or pellets after every few mouthfuls to return later and hungrily eat more.

• Interest in water drops. Water consumption may even drop below normal.

• Temperature passes for normal.

• May seem uncomfortable or sit in litterbox for extended periods of time when this had not previously been a habit. May prefer tunnel boxes or other shaded play or sleep areas to balance of living area.

• May have clear ocular discharge. If so, eye will appear only mildly irritated.

• Top of nose may look as though the rabbit has rubbed it pink and taken off a few hairs in the process.

7-10 Days

• May seem intermittently confused, cross, or unwilling to cooperate with companions or caregiver to complete usual routines.

• If not normally inclined to snuggle or otherwise seek out caregiver's affection, may do so with increasing urgency.

• Interest in water increases but consumption does not.

• Interest in food increases but actual consumption begins dropping.

• Fecal pellets begin to decrease in size.

• Interest in hay increases but if observed for extended periods, chewing and swallowing is slower than usual.

• May continue to sit in litterbox more than usual and/or find places to prop head up. Rarely stretches out to rest, sitting upright nearly always with changes in posture or position rare.

• May seem stiff or move about with clear effort.

• Ears may feel icy and rabbit may present as dazed or dopey if awoken from sleep.

• If had a weepy eye, slight increase in lid swelling.

• May develop a clear nasal discharge.

• May develop small linear welts on the nose above the nostrils or small pink bumps that resemble pimples.

• May develop blister-like lesions on abdomen and/or around genitals.

10-14 Days

• Eating and drinking take longer and the actual volume consumed continues to drop dramatically. May observably have trouble chewing, lapping water and/or swallowing.

• May exhibit initial interest in newly presented food followed by a discouraged attitude and refusal to eat more than a bite or two at most.

• Visits to water dish or bottle increase.

• May have difficulty urinating; urine may appear brown (not the brown associated with carrots, red leafy veggies, or some rabbit pellets).

• Muscle tone and firmness of body decreases.

• May develop a distinct musky "sick" odor.

• Skin may present with stippled bruising effect as coagulation is affected.

• If genitals, anus, nostrils, lips, eyelids, or ears are going to swell, the swelling will become increasingly evident.

• Fecal pellets become even smaller and on days 13-14 may include thick mucous usually indicative of an irritated bowel.

13-14 Days

• In the Vallejo case, on their final day, 5 of the 6 hung over their water dish, eventually lying down in front of the bowl, resting their chin on its edge.

• With favorite greens (for instance), may mouth the food but upon close observation, food is left intact and uneaten.

• May have apparent difficulty holding head up; prefer to lie on belly with chin resting on floor, companion, or toy.

• Tongue may swell and become purple in appearance.

• Temp spikes to 105° F (40.5° C) and above.

• Breathing becomes raspy.

• May run at random if free of cage/pen as though attempting to outrun something; may seek dark areas to hide or caregiver for solace.

• If rabbit lifted, may feel to caregiver as though body cavity filled with pudding or other gelatinous substance.

• May convulse as struggle to breathe through swollen airways and/or as blood vessels give way and they bleed out into chest cavity.

In the 2002 Vallejo case, six rabbits were confirmed lost to myxomatosis out of a total population of 25. In the Sebastopol case, four rabbits were confirmed myxo deaths out of a total population of 13. However, in each case, the caregivers and treating veterinarians attempted to fight myxo and the spread of myxo within each herd by utilizing a drug that had been used by one Australian vet with some success earlier in the year. That drug is Equimune I.V., manufactured by the Canadian-based company Bioniche Animal Health Research, Inc., and licensed for veterinary use in the U.S. against certain diseases in horses. It is a mycobacterial cell-wall extract with the effect of boosting the immune system, thereby allowing the body to more effectively fight off whatever virus infects it.

In the 2002 Vallejo case, we began a three-week course of Equimune I.V. after the fourth rabbit had died of myxomatosis. Two more died in the next two weeks from myxo. Rabbits five and six both had chronic upper respiratory problems and so, I believe, suffered from compromised immune systems.

This left 17 of the original 25 rabbits in that household. In addition to the Equimune I.V. injections administered to the front forepaw intravenously at weekly intervals for three weeks, the rabbits' caregiver raised the temperature of their living space to 80° F (26.6° C) -- another tactic reported as helpful to rabbits infected with myxomatosis.

As of April, 2003 -- four months later -- 15 of the 17 surviving rabbits are well and symptom-free. Prior to the first Equimune I.V. injection, several of these rabbits presented with early onset myxo symptoms, including ridges on the nose, elevated temp, lethargy, and changes in appetite. One rabbit even had very slightly swollen eyelids. Both the caregiver and the treating veterinarian in this case believe that by boosting these rabbits' immune systems, Equimune I.V. was instrumental in their recovery and survival.

Unfortunately, in the 2002 Vallejo case, more than three weeks following the last Equimune I.V. treatment, Sherman, an older rabbit (whose life companion had perished from myxo) fell ill. He died within two days and his tissue was sent postmortem to be tested for myxo. The pathologist, Dr. Fiskett at Idexx Labs, suspected that Sherman had had a toxic reaction to the Equimune I.V. injections.

She explained that years ago an adjuvent called "Freund's Adjuvent" was commonly used. (An adjuvent is something that is added to a drug or vaccine in an attempt to make it more effective.) When Freund's Adjuvent was used in injections administered under controlled conditions to lab rabbits, 10 percent of those rabbits developed internal and/or external granulamatous lesions or abscesses. Freund's Adjuvent is a mycobacterial cell-wall extract, just as is Equimune I.V. Sherman's liver was riddled with granulamatous lesions and he had developed a granulamatous abscess in his lungs.

Two weeks later a younger rabbit, Beau, also fell ill and died. A necropsy showed the same sort of liver damage, and he also had a large granulamatous abscess in his lungs.

Within days of Beau's death, a third, 9-month-old rabbit presented with a fast-growing tumor on her ankle. Upon surgical removal, it proved to also be a granulamatous abscess. As of April 2003, this rabbit seems well.

In the Sebastopol case, the caregiver and treating veterinarian decided to administer the Equimune I.V. only twice, intravenously, at weekly intervals.

None of the surviving rabbits in that household have manifested any side effects.

These cases are hardly a scientific trial of Equimune I.V. The outcome is inconclusive and it would not be scientifically valid to credit the treatment of those rabbits with Equimune I.V. with their survival.

However, I feel that should a caregiver and veterinarian determine that a rabbit is presenting with early symptoms of myxomatosis, the caregiver and veterinarian might wish to consider utilizing Equimune I.V.

Update 2003

In mid-July, yet another rabbit in Sebastopol was confirmed to have died from myxomatosis. This rabbit's caregiver took him to the vet who treated in the 2002 Sebastopol case, who easily identified his end-stage symptoms and then confirmed via postmortem lab work.

Most of the California experts on myxo have said that they see myxo most frequently in the autumn, so I read this death (possibly only one of many, but this one actually reached a vet, was recognized as myxo, and was reported to the local HRS chapter) as a predictive factor for autumn. It is imperative to keep rabbits indoors and not let them outside this year; I believe the risk will only increase as the year progresses.

You are welcome to call the Solano/Sonoma chapter of the House Rabbit Society (707-643-2852) with questions, and if you find yourself faced with the decision of whether or not to try Equimune I.V., your veterinarian may call Beth Owen, DVM, the treating veterinarian in the 2002 Vallejo case, for dosage and source information (707-553-8363).