VetInfo Digest            May 2001

This Month:

Vets and Vaccinations

Foot and Mouth Disease

West Nile Virus

BSE or "Mad Cow Disease"

Bile Acids and Actigal (Rx)

Rethinking Things:

Cats With Cystitis

Adding Fiber to the Diet

Itch Control and Allergy Immunotherapy

Splenectomies

Immune System Stimulants

Isoflurane Anesthesia

New Generic Medications

Reasonable Expectations

Over the last few months we have mostly been reporting difficulties in keeping up with the volume of questions from the web site. I am happier this month reporting that we finally seem to be in a catch-up mode. I am really hoping to be back to answering questions within a few days by the end of May. I appreciate the patience and kindness of so many of you during the last few months. We still have a few questions from early in April that have not been answered but I will hopefully be getting to them very soon.

I did put off getting the VetInfo Digest finished for May for a few days to devote time to catching up, so it is a few days late coming out this month. Hopefully, that won't happen again any time soon, either.

I am going to spend a little time this month on several diseases that don't really affect dogs and cats but which have been constantly in the news over the last few months. For some of you, who have been following along closely, this may be old news. I am hoping that as questions arise the information will still be valuable, though.

Vets and Vaccinations

We have changed our routine vaccination schedules for both dogs and cats to an every three year cycle, rather than yearly vaccinations. We did this in cats to try to reduce the incidence of vaccine associated cancer (sarcomas) and in dogs because there is some evidence that immune mediated hemolytic anemia is more common in the month following vaccinations in dogs than at any other time. Duration of action studies of vaccines commonly used in both dogs and cats have been done and do indicate that the vaccinations provide protection for several years. With the presence of known potential dangers from vaccines along with good evidence for a longer duration of effect, we feel compelled to go to a longer vaccine interval medically. Financially, though, this has been hard on our practice.

Vaccinations have been between 15 and 25% of the gross income of our practice throughout most of the years we have been in practice. We stopped vaccinating cats on a yearly basis about two years ago. We stopped vaccinating dogs on a yearly basis last November. This year, so far, vaccinations account for about 6.5% of our gross practice income. Our gross income is down roughly 5% from previous first quarter figures. While this could be due to a multitude of factors, we feel strongly that the decrease in vaccine income is a major factor, especially since many of our clients opt to skip the yearly physical exam when vaccinations are not due. This is more of a problem with the dog owners than with cat owners, probably because we can hand scale the tartar on most cat's teeth during an examination which gives the visit a higher "perceived value" among cat owners. We do not feel that we can hand scale dog's teeth very successfully, so we do not do this during the yearly physical examination for dogs. We are not sure, but we think this may partially account for the larger percentage of dog owners who do not respond to yearly physical exam reminders when their dogs are not due for vaccinations or other treatment. Another possible factor is the feeling among many dog owners that they are capable of telling when their dog has a problem, while cat owners seem to accept that cats might choose to hide an illness or at least tolerate it to the extent that it isn't obvious.

It is likely that vaccine income will continue to be much lower than in the past. This will eventually mean that we have to raise prices in other areas to cover this loss, or develop other health services that replace the income formerly derived from vaccinations. We are trying to emphasize some other health issues that have been ignored in the past in order to conserve money for vaccinations. Teeth cleaning is an important part of health care and should be done on a regular basis. Heartworm prevention in cats is a good idea but may appear too costly to some people when added on the top of other necessary care, including vaccinations. To some extent there should be more money available for these and other more advanced health care problems as the result of fewer vaccinations. We continue to hope that people will put the money they save from vaccinations into better health care for their pets.

Foot and Mouth Disease

Foot and Mouth Disease (FMD) is a viral illness that affects cloven hooved animals. In rare instances it has been suspected to cause sores in humans working directly with cattle, sheep or pigs but in general this is not a disease of humans, dogs or cats. Ordinarily, that would make it a disease that we wouldn't cover in the VetInfo Digest but I am getting so many questions from clients about this disease that I thought it might be best to at least cover the basics.

FMD is caused by a picornovirus. It causes sores on and in the mouth, on the feet and on the teats of affected animals. It is probably the most contagious viral illness of animals. There are reports of FMD virus being transported 100 miles by wind alone and it can travel on clothing, shoes, farm machinery and in infected meat or milk. From the time an animal is infected until clinical signs appear varies between 2 and 14 days. Viral shedding may start before clinical signs appear, though. The high infectivity of the virus and the latent period are the reasons that there is such an aggressive effort to control the virus, including killing animals on farms neighboring ones in which the infection has occurred. The disease is found in South America, Europe and Africa.

If Foot and Mouth Disease were to make it to the United States the effect on our farming economy could be enormous. It is likely that an outbreak will occur at some time, but there are some things that you can do to help prevent the spread of the virus. These are especially important if you are planning on taking a trip to England or France this summer.

A common question asked at our practice is "why not vaccinate the cattle for this disease?" There are two major reasons for the reluctance of health officials to allow vaccination. One is that that there are a number of strains of FMD virus and vaccination with one strain may not protect against others. Another reason is that vaccinations appear to prevent clinical signs of this disease without preventing infection. Infected animals are then very difficult to identify and spread of the disease is easier. If vaccines are used it makes it almost impossible to export cattle, sheep, goats and pigs from a country in which Foot and Mouth Disease occurs since importing countries can not be assured that the animals are not infected with the virus. Due to the long term effect on the economy by introducing vaccines, health officials tend to be willing to accept huge short term losses in order to avoid a long term ban on livestock and meat exports.

It is important to keep Foot and Mouth Disease out of uninfected countries, including the United States, so if you go to England or any other country in which FMD occurs, be careful to ensure that you do not bring the virus home with you. Being cautious could save millions of dollars.

West Nile Virus

The West Nile encephalitis virus (WNV) is part of a viral family, Flaviridae, that includes the Japanese, St. Louis, Rocio, Murray Valley and Kunjin encephalitis viruses. Prior to 1999 it appeared to be confined to Africa, Europe, the Mid-East and a small portion of Asia. Since 1999 this virus has been found on the East Coast of the United States and may have been present prior to that time without being documented. The disease most commonly infects horses and humans. It appears to be spread exclusively through mosquito bites in the United States but has been found in ticks in other areas on which it occurs. There is at least one species of mosquito in the United States (Culex) which can harbor the virus throughout the winter months and spread it again in warmer weather the next year. While it is not possible at this time to say with certainty whether West NileVirus is going to be able to establish a permanent status in the United States it appears likely that this could happen. If some of the known vector mosquitos for the Faviridae family viruses become established in the United States it would make it easier for the virus to become a permanent resident. This is not an unlikely problem, as several species of mosquitos have spread to the United States in the last decade or so.

There is a documented case of WNV occurring in a dog in South Africa and at least two cats found dead on the East Coast were infected with this virus. While the risk to any individual dog or cat appears to be very low it does not appear to be impossible for this virus to infect dogs and cats.

There have been over a hundred human cases of WNV in the U.S. and horses have also been infected at higher rates than most other species. The West Nile virus is different from the encephalomyelitis viruses that are commonly vaccinated for in horses. At the current time there is no vaccine for this particular virus. It is thought that most horses have minor infections and recover but there have been recorded deaths in horses in the U.S. from this virus since it was first identified here in 1999.

The signs of WNV in horses include depression, lethargy, loss of balance, stumbling (ataxia), weakness and paralysis. If these signs are seen in any of the areas in along the East Coast in which the virus has occurred it would be best to consider the possibility of West Nile virus, although other diseases can cause similar signs.

There is some confusion among horse owners about WNV because it seems like it might be just another in the line of equine encephalitis viruses that horse owners have been vaccinating against for years, including Western equine encephalitis (WEE), Eastern equine encephalitis (EEE) and Venezuelan equine encephalitis (VEE). These are a completely different family of viruses, though. There is no protection against WNV from vaccination for WEE, EEE or VEE.

The best protection against the spread of West Nile virus is mosquito control. Keeping horses and pets in at dawn and dusk, using mosquito repellents in areas in which mosquito populations are high and controlling mosquito breeding areas by eliminating standing water to keep mosquito breeding spots to a minimum. It is considered to be safe to care for horses or pets that have been infected with the virus since the disease must be spread to humans by a mosquito bite.

This disease does look like it is one that we will have to learn to live with in the United States, at least along the East Coast.

Bovine Spongiform Encephalopathy or "Mad Cow Disease"

Bovine spongiform encephalopathy (BSE) is a disease that is believed to be caused by a recently recognized problem with a normal cell protein (referred to as the prion protein) mutating or changing in some other fashion so that it causes increased production of similar protein, which interferes with cell function and causes cell death. Since the prion protein is most common in neurologic tissue, clinical signs are associated with the nervous system. Prion protein is different than a virus, which is composed of nucleic acids (the building blocks of DNA and RNA). Some scientists do not believe that a protein is capable of causing the cell to produce more of itself without the aid of a virus or other infectious agent.

A disease in sheep, referred to as scrapie, is thought to be the underlying cause of BSE. In Britain and in some other countries, it has been common practice to feed meat and bone meal made from sheep to cattle. This may have led to a situation in which prion proteins associated with scrapie adapted enough to infect cattle. The end result of infection with BSE is destruction of brain tissue leading to the brain looking somewhat like a sponge when it is examined. This leads to neurologic disease, including marked nervousness, fear of familiar objects or situations, aggressive behavior, difficulty walking, tremors and death.

There is a disease in humans referred to as Creutzfeldt-Jakob disease (CJD) that is very similar in appearance to BSE. This disease occurs in a small number of people and currently is thought to occur as the result of a similar problem in humans in which there is an increase in prion protein, possibly as a natural mutation. CJD historically was a disease of older people. In recent years a new variant of this disease (nvCJD) has occurred, that seems to attack younger people and to develop much faster than CJD has in the past. This new variant of CJD is possibly due to infection of humans with BSE. There are recognized transmissible spongiform diseases (TSDs) in cats, mink and some wild animals such as antelopes. Feline spongiform encephalitis (FSE) occurred in Britain with increasing frequency at about the same time that the nvCJD problem surfaced and it is hypothesized that both diseases occur due to exposure to BSE contaminated beef products. Both nvCJD and FSE are decreasing in frequency since BSE has been recognized and control measures instituted.

There are still medical researchers who do not believe that prion proteins are an infectious agent or believe that if they are, they must be activated by a virus or other infectious agent among those we have recognized for some time. There is no absolute evidence to confirm that BSE can be transmitted to other species. There is very good circumstantial evidence to suggest this, though. The strongest link being that new variant Creutzfeldt-Jakob disease has only been recognized in areas in which BSE occurs. Bovine spongiform encephalopathy had a devastating effect on Britain's cattle market. Due to the economic situation, there will almost have to be ironclad proof of a causal relationship between BSE and nvCJD before public officials are willing to make statements strongly linking these diseases. It is reasonable to assume that there is likely to be a link at this time, though.

If BSE can cause similar disease in humans who have ingested meat products contaminated with the infectious form of prion protein, or whatever the infectious agents are, there is going to be some risk of infection in humans for as long as the disease exists in cattle around the world. The actual risk for a person residing in the United States or other areas in which BSE has not been found, or for pets eating pet foods produced in such areas, is so low that it is virtually nonexistent at this time. For most other countries in which sheep bone or meat meal was not fed to cattle and in which cattle are not infected, so that meat meal from cattle fed to cattle is also safe, there is not much chance of people or pets contracting a transmissible spongiform disease.

The risk in Britain appears to be decreasing with the recognition of the significance of the BSE problem but there are new cases being reported of both BSE in cattle and nvCJD in humans in Britain at this time. Almost all the countries in Europe have had at least a few cases of BSE, with Ireland and Portugal reporting over five hundred cases since the disease was recognized and less than ten cases in Italy, Denmark and the Netherlands. Other European countries have reported numbers between these extremes. There is one reported case in a cow exported to Canada.

It seems likely that BSE will not spread to countries in which it has not been previously reported to any great degree and that it will be controlled in Great Britain and other countries in which it has occurred as feeding practices change and infected cattle are culled from herds. Despite this, it is important that research continue into the prion protein's role in this disorder since this is a newly recognized disease process.

Bile Acid Assays and Actigal (Rx)

When testing for bile acid levels in a patient that is already on ursodiol (Actigal Rx), it is necessary to stop the Actigal for a few days prior to testing for bile acids because Actigal is a synthetic bile acid and may be measured by the test procedure.

Rethinking Things

In trying to figure out how this might be, I ran across several veterinarian's opinions that mask induction of dogs and cats with isoflurane could cause problems in some cases, especially when the pet struggled hard or was extremely upset during the anesthetic induction with the gas. A number of veterinarians have stopped using mask anesthetic induction (using only anesthetic gas to cause anesthesia) and switched to using injectable anesthetic induction agents to decrease the stress associated with mask inductions. We continue to use mask inductions in our practice as we find we can do this without a struggle in most cases. We have started giving up mask induction in individual patients as soon as it is evident that the pet is not accepting the technique well, though.

Isoflurane can be a little difficult to monitor compared to other anesthetic gases, because patients are often appear to be in a deeper plane of anesthesia than they really are with isoflurane. Some of the risk of using this anesthetic appears to be due to this property of the gas. Surgical procedures may be initiated prior to the time the pet is fully anesthetized if the veterinarian is not aware of the ability of this anesthetic gas to render a patient immobile prior to the time they are unable to feel pain. If this happens, there is an increased risk of shock.

Since we have been strong advocates of mask induction, believing in an increased safety margin for using only isoflurane gas, this study definitely caused us to rethink our position on isoflurane. It also makes me realize that there isn't a "best" anesthetic that applies to all situations. Veterinarians who are very familiar with the use of other anesthetic medications may be better off using them, rather than trying to a learn how to use a new anesthetic, even if is considered to safer for general use.

New generic medications

In the last few months several medications have gone off patent and are available in generic form. The list includes methimazole (Tapazole Rx), selegiline (Anipryl Rx) and enalapril (Enacard Rx, Vasotec Rx). The veterinary medications Anipryl and Enacard are still on patent but the human equivalents have become available in generic form. It may be less costly to use the generic versions of these medications. As with all generic and brand name comparisons there can be factors which make the name brand better in some circumstances. If your pet is on one of these medications it is reasonable to ask your vet about switching to a generic version. If your vet objects to the use of a generic medication for your pet's condition listen to the reasoning to see if you understand the reasons for staying with the brand name.

Expectations

Sometimes I worry about the expectations that my clients bring to the office. I think that many of my clients actually believe that I am able to make an accurate diagnosis of their pet's condition based on a physical exam alone. Others are pretty convinced that if I take X-rays of their pet and run blood work, I must be narrowing the field of possible diseases and disorders to the point that I can say with certainty what their pet's ailment is. This simply isn't the case.

When a pet comes to the office we try hard to determine why the client brought the pet to the office in the first place by asking a series of questions. If the client is helpful in answering the questions and if I ask the correct questions, it is possible to narrow the possibilities for a pet's condition down to a reasonable number of diseases or disorders. From the list of remaining choices, which vets often refer to as the "rule out" list, I have to devise a plan to discover which of the illnesses are unlikely and which ones are very likely.

If I am allowed to do a routine chemistry panel, a complete blood count and other test procedures more specific to the problem at hand and to include all the disorders on the rule out list as possible diagnoses and then claim to be correct if any one of them turns out to be the problem, I think that I could make an "accurate" diagnosis in about 90% of the cases that we see in our clinic. Even with a good physical exam, lab results, X-rays and other test procedures I know that there are going to be disorders that I simply can not identify with certainty. Mystery illnesses are frustrating but they are part of life in the medical professions.

I think that most of my clients wouldn't be overly satisfied with a list of twenty possible problems and a bottle of pills that might cure one of them, though. So I usually end up giving people a short list of the most likely problems and picking one of them that I feel is really likely to be the problem and emphasizing it. I am pretty certain that my first guess is incorrect in at least a third of my clients and the percentage may be higher than that. I know that many clients would be horrified if they realized just how inaccurate I consider my clinical judgment to be, but I suspect that it is at least average and possibly above average among veterinarians.

My ability to accurately diagnose a problem increases with each return office visit, especially if I can continue to run lab tests on subsequent visits as symptoms change and response to treatment can be evaluated. Nature works on my side, because time really is a good healer. Sometimes I get credit for being right when a patient improves despite my efforts, instead of because of them. This is balanced by the times when I am right about a diagnosis but the patient refuses to respond to appropriate therapy, though. Even with the best of luck, though, I know that I am incorrect in my diagnosis of my patient's conditions in many cases, especially early in the diagnostic process.

Veterinarians are humans. There are many possible illnesses for almost all clinical signs that occur in pets. It is unrealistic to expect that a veterinarian is going to be correct in making a diagnosis every time. What you should expect is that your vet will continue to work with you as new symptoms emerge, as response to treatment can be evaluated and that your vet will keep an open mind about other possible illnesses when therapy is not going well. In addition, as time goes on, your vet should be willing to research difficult cases and discuss the research findings with you. When it becomes clear that progress is not being made, despite your vet's best efforts, he or she should be willing to make a referral to a board certified specialist or to another veterinarian who has a strong interest in the area of medicine that seems appropriate for your pet's care. Accuracy in the early diagnosis is not nearly as important as a willingness to continue to search for the right diagnosis over time. This process works better when the client is able to recognize that there is an ongoing process and that it is important to keep working with the vet to achieve the best outcome for their pet. If you are realistic in your expectations it will help you through the frustration that often occurs when progress towards a cure seems slow at first and help you to avoid going from one vet to another without allowing any of them the time to work through a good diagnostic effort.

Thanks for Your Support!

If you send us e-mail, remember that Michal Justis answers the e-mail at vetinfo@vetinfo.com. E-mail sent to mervet@inna.net is answered by Dr. Michael Richards.

The VetInfo Digest is published by TierCom, Inc., P.O. Box 476, Cobbs Creek, VA 23035. The opinions expressed in this newsletter are those of Michael Richards, DVM., author.

Copyright 2001, TierCom, Inc.

Dr. Schultz at the University of Wisconsin