Researchers at Colorado State University’s (CSU) James L. Voss Veterinary Teaching Hospital are seeking feline study participants for a novel stem-cell therapy that could repair the damaged organs of cats with chronic kidney disease.
The study involves injecting feline patients with stem cells cultivated from the fat of young, healthy cats, and has shown promise for treating a health problem that affects approximately 50 percent of cats older than 10, CSU said.
Jessica Quimby, DVM, leader of the CSU research, said the current undertaking is designed to further test the efficacy of the treatment now that previous research at the school has established a strong safety profile.
“In our pilot study last year, in which stem cells were injected intravenously, we found stem-cell therapy to be safe, and we saw evidence of improvement among some of the cats enrolled in the trial,” Quimby said in an article published in Phys.org. “In this study, we will further explore stem-cell therapy with the new approach of injecting the cells close to the damaged organs. We hope this proximity could yield even better results.”
According to Quimby, her group’s prior research has demonstrated that the stem-cell treatment could decrease inflammation, promote regeneration of damaged cells, slow loss of protein through urine, and improve kidney function.
Adult stem cells are cells found in various tissues throughout the bodies of both juveniles and adults. By definition, these are undifferentiated cells that can be induced to become any of a number of cell types.
Bone marrow-derived mesenchymal stem cells (BMDMSC) are of particular interest in orthopedics, as cells in this lineage are involved in osteogenic differentiation of cells at the site of bone generation and regeneration. These cells, by virtue of their presence in bone marrow, have easy access to sites of fracture healing. However, only a small fraction (fewer than 0.01 percent) of the cells present in bone marrow are BMDMSC. A bone-marrow aspirate may contain only a few thousand cells — not nearly enough to incite a significant osteogenic effect. For this reason, investigators are expanding these cells in culture to obtain numbers in the millions. This number of cells has been shown to induce bone healing.
Photo 1: Dèbridement of fibrous tissue from a delayed union site using a bone curette through a limited approach.
Bone marrow-derived mesenchymal stem cells can be obtained by harvesting bone marrow from a patient and growing that patient’s cells in culture in a laboratory. These are referred to as autogenous cells, or cell autografts. However, this is difficult to do in a clinical setting in which a laboratory is not available for immediate transfer of the marrow sample. There is a large body of experimental data demonstrating the safety and efficacy of BMDMSC from another individual of the same species, referred to as cell allografts. This newer approach will make it easier for clinicians in various practice settings to use these cells, not only for bone healing, but for regeneration of other tissues as well.
Photo 2: Identification of site of dèbridement and stem cell delivery using a percutaneous approach with fluoroscopic guidance.
Bone marrow-derived mesenchymal stem cells can be grown in a commercial or academic laboratory and used by veterinarians at distant locations by shipping the cells via overnight courier on dry ice.
Photo 3: Providing access to marrow elements at the site of impaired bone healing by drilling small holes in sclerotic bone.
There are a number of clinical scenarios in which a minimally invasive, biologic approach to tissue regeneration carrying low risks is desirable. These cells can be delivered to virtually any anatomic site via a percutaneous approach. For example, this system can be utilized in any delayed or non-union fracture site, as well as in slowly fusing arthrodesis sites.
Photo 4: Delivery of stem cells via a limited approach
The delivery site should first be dèbrided (Photo 1) to remove all fibrous tissue that may impede osteogenesis. This dèbridement can be accomplished with a percutaneous approach using fluoroscopic guidance (Photo 2), or a limited open approach. Provide access to the marrow cavity by drilling small holes in any sclerotic bone at the site (using 0.045-inch Kirschner wires, Photo 3). This preparation provides access to the patient’s own stem cells, which may undergo osteogenic differentiation in response to delivery of the allograft BMDMSC. The allograft BMDMSC can be delivered through the same percutaneous or limited open approach (Photo 4), further compromise the vascular supply to the bone and soft tissues.
Photo 5: Allograft stem cells delivered from an academic or commercial laboratory following expansion in vitro.
The cells (Photo 5) can be delivered in a number of carrier systems designed to retain the cells at the site of interest, to make delivery through a percutaneous approach easy and safe and to augment the osteogenic potential of the cells.
Photo 6: An example of a mixed carrier system for delivery of stem cells.
Examples of such carrier systems that have been used with success with BMDMSC include: absorbable collagen sponge, absorbable gelatin sponge or powder, autograft cancellous bone, allograft cancellous bone, autograft and/or allograft corticocancellous bone, autologous bone marrow and any combination of these carriers (Photo 6). Radiographs should be taken four weeks status post stem-cell delivery to assess the progress of bone healing. The need for further follow-up will vary depending on the nature of the case, the age of the patient and the robustness of the initial response to stem-cell therapy.
Dr. Zachos is an ACVS board-certified surgeon. She is assistant professor of orthopedic surgery at Michigan State University, where she is an attending orthopedic surgeon in the Small Animal Clinic of the Veterinary Teaching Hospital. She also runs a molecular orthopedics laboratory at Michigan State. Her research focus is the development of translational cell-based gene therapy techniques for bone and cartilage regeneration.
Her work has been recognized by the American Academy of Orthopaedic Surgeons, the Orthopaedic Research Society, the Ruth Jackson Orthopaedic Society and the 7th International Conference on Bone Morphogenetic Proteins.
Dr. Smith is a resident in small-animal surgery at the Lois Bates Acheson Teaching Hospital, Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University.
|Feline injection-site sarcoma, or FISS, is a controversial topic; however, Dr. Richard Ford presents a comprehensive overview of the history, literature, and current issues associated with FISS. In addition, two very interesting questions are answered: W hat do we still need to learn about FISS and how do we lessen the risk for its development in cats?
Richard B. Ford, DVM, MS, Diplomate ACVIM & ACVPM (Hon)
|Figure. Postoperative cat with FISS at FeLV vaccination site. The tumor developed in skin over the left side of the pelvis, indicating an injection site high on the left side. Tumors that develop at this level pose a serious risk for invasion of the ileum if not treated early.
Today, among the spectrum of vaccine adverse events reported in dogs and cats, feline injection-site sarcoma (FISS) ranks as the most serious. Although it occurs infrequently, the consequences of a malignant tumor developing at a vaccination site are devastating to the patient and owner.
Consider the following facts:
HISTORY OF INJECTION-SITE SARCOMAS
Electron probe microanalysis of tumors identified aluminum (commonly used as an adjuvant in feline vaccines) within macrophages surrounding the sarcomas. The hypothesis was advanced, but not proven, that persistent inflammatory and immunologic reactions to aluminum adjuvants might lead to neoplastic transformation in cats.5
Adjuvants Role in Pathogenesis of FISS
At the time the study was conducted, all FeLV and rabies virus vaccines licensed for cats in the U.S. were inactivated, adjuvanted products. This fact raised concerns that chronic inflammation caused by adjuvant-containing vaccines, rather than one particular vaccine brand, played a role in the pathogenesis of these tumors.
Since the early days of vaccine-associated sarcoma (now known as FISS) discovery, several studies have been published that characterize tumor pathology, offer diagnostic recommendations, outline treatment options for affected cats, and assess survival rates.
A brief chronology of FISS is presented in Table 1.
ISSUES & CONTROVERSIES
Other Causes of Sarcomas
These observations support the fact that chronic inflammation, due to a variety of causes, may lead to oncogenesis in some cats.
Roles of Genetics & Adjuvants
Vaccine Selection Challenges
In addition, in the U.S., there is only 1 nonadjuvanted (recombinant) vaccine each for FeLV and rabies virus (only available as a 1-year vaccine). These vaccines are priced higher per dose than adjuvanted (killed) FeLV and rabies virus vaccines, a factor that influences purchasing decisions.
WHAT IS STILL UNKNOWN
Prevalence estimates from 1 in 10,000 cats to as many as 1 in 1000 cats have been cited. Studies reporting risk according to doses of vaccine administered/sold also vary (from 1 to as many as 36 cases per 10,000 doses).11-16
Reliably tracking and reporting prevalence, or the proportion of cats in the population that develop tumors subsequent to vaccination, are critical in learning whether recommendations to reduce or eliminate risk are effective over time. Tracking prevalence of FISS has proven challenging due to several reasons, including: low/inconsistent reporting of FISS, lack of a centralized database, and genetic influence.
Pathogenesis of FISS
What isn’t known is how these factors interact in the individual cat, leading to tumorigenesis.
Mutations in the TP53 gene of some cats with FISS have been detected in studies conducted at the University of Minnesota. Although these studies suggested potential for assessing genetic predisposition for FISS, there is no commercially available test that will reliably predict which cats will develop tumors.
Nonsurgical Treatment Options
Due to the fact that injections other than vaccines can induce tumors in cats, it becomes reasonable to seek nonsurgical treatment and management options to limit the consequences of surgery. At this time, medical treatment of FISS offers limited value to the individual patient, even when combined with radiation therapy.
MITIGATING RISK FOR FISS
Note that the following succinct review of recommendations has appeared in the literature and been presented at national conferences over the past several years; however, the recommendations have not consistently been subjected to scientific scrutiny and often represent expert opinion rather than results of published studies.
Only administer vaccines when reasonable risk of pathogen exposure is apparent.
Among adult household cats that have completed the initial vaccination series, core vaccines (feline parvovirus-herpesvirus 1-calicivirus) should be administered at 3-year intervals. Rabies vaccine should be administered according to state or local statutes and at an interval consistent with the product label. Only administer noncore vaccines to cats with realistic exposure risk.
Only administer parenteral vaccines by subcutaneous route.
Administer vaccines in accordance with current vaccination site recommendations.
Obviously, the recommendation to inject vaccines at distal limb sites is intended to facilitate complete removal of the tumor and minimize the risk of local recurrence, following amputation of the affected limb.
Educate clientele about reporting postvaccination lumps.
Manage postvaccination lumps in accordance with the 3-2-1 Rule (Table 2).
Perform routine thoracic radiographs in cats confirmed to have FISS.
Avoid the use of adjuvanted (inactivated) vaccines whenever feasible.
The hypothesis linking adjuvant-induced chronic inflammation to sarcoma formation has been suggested by several authors beginning in the early 1990s.3-5 Controversy over the role of adjuvant in sarcoma pathogenesis intensified with the publication of a limited number of studies suggesting there was no significant difference in FISS risk posed by adjuvanted versus nonadjuvanted vaccines.10,11,19 No studies have been published that suggest an adjuvanted vaccine is safer than a nonadjuvanted vaccine, with respect to FISS risk.
The controversy surrounding safety of administering nonadjuvanted vaccines over adjuvanted vaccines is likely to continue. The scientific evidence simply isn’t available currently to support unambiguous conclusions. The consequence is that cats will continue to be diagnosed with FISS attributed to routine vaccination.
Despite continuing controversy, the fact—that sarcoma diagnoses in cats became more common as the use of adjuvanted vaccines became more prevalent—remains a critical and undeniable piece of information that highlights a potential role for adjuvant in the pathogenesis of FISS. The recommendation to avoid adjuvanted vaccine in cats whenever feasible is justified.
AAHA = American Animal Hospital Association; AVMA = American Veterinary Medical Association; FeLV = feline leukemia virus; FISS = feline injection-site sarcoma; VAFSTF = Vaccine-Associated Feline Sarcoma Task Force
By Linda Fiorella
There’s a well-known scene in the movie Jaws where Richard Dreyfuss’ character cuts open the belly of a shark and pulls out some unexpected items, including a Louisiana license plate. As some pet owners and all vets know, an X-ray of a pooch’s stomach is also likely to produce some surprising findings.
While some dogs may try to eat pretty much everything, one thing that seems to hold a strong attraction for many dogs across a variety of breeds is cat food.
Dog and cat foods may seem pretty similar on the surface, but there are some important differences. Cats are obligate carnivores, meaning they need to eat meat as their main food source, whereas dogs are omnivores and need a diet with more fiber than a strictly carnivorous diet can provide. Still, there is meat in dog food, too, so why do dogs crave their feline friends’ food so fiercely?
“Since dogs can’t tell us why they love cat food,” says Sharon Crowell-Davis, DVM, DACVB, professor in the College of Veterinary Medicine at the University of Georgia, “and it is pretty consistent amongst most dogs (they just really do love cat food!), I’m going to guess it’s the higher protein content and the effect it has on the flavor.”
Dr. Crowell-Davis even uses cat treats as incentives for some of her canine behavioral patients because the deliciousness galvanizes the pups, just as long as “the dog loves them and the dog’s stomach can handle them, and it helps motivate the dog in learning how to behave the way the owner wants it to,” she says.
But just because something tastes good doesn’t mean we should eat it all the time. Dr. Crowell-Davis compares cat food and dogs to cake and humans. “It’s not necessarily the best thing for our diet, and certainly if we ate nothing but cake, we’d become really sick. But as an occasional treat, it’s not going to hurt us.”
But she points out that with some dogs, even as a rare delicacy, cat food can cause problems because dogs aren’t designed to have such a protein-dense diet. “Some dogs will get an upset stomach — vomiting, diarrhea — from eating cat food, while some other dogs with a tougher stomach can handle cat food,” she says. “If your dog breaks into the bag of cat food, is it going to kill the dog? Absolutely not. But if your dog does vomit or have diarrhea, make sure the dog can’t get [into] the cat food again, because it’s obviously one of those dogs whose GI system reacts badly to cat food.”
Even if your pup is one of those with an iron gut, long term it is not good for a dog to eat primarily cat food, Dr. Crowell-Davis says. It’s not properly balanced for them in terms of the fiber and protein and certain nutrients. Plus, it can be hard on their liver and their kidneys to have so much protein. Even more important, though, is the vice versa — make sure that your kitty is not fed a diet of dog food. “There are two essential ingredients in cat food that are not in dog food,” she says. “Taurine is an amino acid that dogs can manufacture in their own bodies but cats cannot, and also arachidonic acid, which is a fatty acid that cats need.”
Virbac has expanded its voluntary recall of Iverhart Plus Flavored Chewables following its initial recall notice in April 2013.
According to PetMD, additional specific lots of the heartworm preventive are being recalled because they might not fully protect dogs in the upper third of each weight range.
PetMD cited a letter distributed by Virbac saying that 14 lots of Iverhart Plus Flavored Chewables were below Ivermectin potency levels prior to their expiration. Another 17 lots are being recalled out of caution even though they remain within specification.
Virbac is recalling the following lot numbers for each weight range:
Small dogs (up to 25 pounds)
Medium dogs (26-50 pounds)
Large dogs (51-100 pounds)
Virbac directs consumers who have questions about the recall to contact Virbac Technical Services at 1-800-338-3659, ext. 3052.
Christy Corp-Minamiji, DVM
For The VIN News Service
In the world of canine heartworm disease research, reluctance to use the R word has evaporated. Leading authorities in pet parasites now concur that resistance to the class of drugs used in heartworm preventive drugs is real.
“We now have proof there is resistance to the macrocyclic lactone (ML) class,” said Dr. Byron Blagburn, an Auburn University parasitologist who did much of the research on strains of heartworm found in the Mississippi Delta, where loss of efficacy to preventive drugs was first suspected. “It’s accepted by the entire industry now,” Blagburn said.
This recognition has placed the industry in uncertain territory. While the entire ML class is implicated in the resistance data, variations in product formulation and ingredient combinations may mean some products work better than others.
In an interview with the VIN News Service, Blagburn was careful to distinguish between drug class and drug product. “All preventives contain at least one macrocyclic lactone and at least one product (containing each ingredient in the class) failed. It does seem to involve all major drugs in that category,” he said, “but not all products are equal.”
The question of whether drug-resistant strains of heartworm are emerging in the United States has been scrutinized for years. Until now, however, experts have been careful to avoid using the so-called R word, “resistant,” to describe the strains that appear not to respond as expected to macrocyclic lactones.
Blagburn credits the evolution in understanding of heartworm susceptibility and identification of the resistant strains to “an inter-collegiate, inter-laboratory, collaborative process.”
The consensus is embodied in a recent update by the Companion Animal Parasite Council (CAPC) of its heartworm prevention guidelines. The new text on the CAPC website states: “Recent work has shown that there are isolates of heartworms that are capable of developing to adults in dogs receiving routine prophylaxis with any of the available macrocyclic lactones.”
In short, a dog faithfully given heartworm-prevention medication may still become infested with the parasitic worm Dirofilaria immitis, which inhabits the arteries of the lungs and sometimes a portion of the heart, causing serious and potentially fatal disease.
Convincing evidence of resistance was presented by multiple researchers at a meeting of the American Association of Veterinary Parasitologists in Chicago last month, according to CAPC President-elect Dr. Susan Little, a veterinary parasitologist at Oklahoma State University. Although research has focused on heartworm isolates from the South and Southeast, the CAPC notes that “At this time, the geographic extent of these resistant heartworms is not known.”
The macrocyclic lactone class of drugs in question comprises avermectin drugs (ivermectin and selamectin) and milbemycins (milbemycin oxime and moxidectin). These drugs are found in all commercial heartworm preventives, including: Heartgard (ivermectin), Tri-Heart Plus (ivermectin), Sentinel (milbemycin oxime), Revolution (selamectin), Advantage Multi (moxidectin), ProHeart6 (moxidectin), and Trifexis (milbemycin oxime).
The resistance finding begs the question: Is there any point to using the products?
Absolutely, say Blagburn and Little. Both state that the preventive products still work very well. There may be breaks in prevention with certain products in certain areas, but to the expert mind, this state of affairs only increases the need for year-round preventive action and annual testing for heartworm disease.
“To make a presumption that because resistance exists, the products should be discontinued is absolutely ludicrous,” Blagburn said.
While increased use of a drug usually is implicated in speeding the development of resistance in target parasites or pathogens, the canine heartworm may be different. With the heartworm, a number of factors work against the propagation of resistant genetics, according to Blagburn. The factors include:
While the spread of resistant genes is inevitable, Blagburn said, drug resistance is likely to spread geographically more slowly than has been the case with related worms, such as gastrointestinal parasites.
The recent heartworm research is notable not only for the multi-institute approach, but because the investigation into reports of product failure was spearheaded by the manufacturer of one of the products in question. In communication with the VIN News Service, Dr. Jason Drake of Novartis Animal Health explained the genesis of the studies:
“In recent years, the U.S. Food and Drug Administration (FDA) has seen an increase in reports of lack of efficacy in all approved heartworm preventive therapies – reports that were from manufacturers and veterinarians,” Drake said. “After listening to the concerns of veterinarians in the Mississippi River Valley, Novartis Animal Health decided to invest in understanding this problem and, if resistance was confirmed, to work with veterinarians to help contain the spread of resistance.”
He highlighted data demonstrating that the entire drug class is affected. “Regardless of which product was used, whether it was oral, topical or injected, protection against some Dirofilaria immitis isolates from the Mississippi River Valley was less than 100 percent for all active ingredients included in the ML class,” he said.
While the entire class of drugs appears vulnerable to resistance, not every product has shown reduced efficacy.
Bayer Animal Health, maker of Advantage Multi, a topical drug that contains moxidectin, said by email to the VIN News Service that while research has shown a failure of injectable moxidectin to protect all dogs in a challenge study, the company is unaware of any published data showing a similar failure of moxidectin product applied to the skin.
Little, the parasitologist and CAPC president-elect, confirmed this. She explained: “The CAPC statement refers to all active ingredients because of the injectable moxidectin data, which have been presented in detail. Topical moxidectin is thought to result in higher plasma levels than injectable moxidectin, so there are likely differences in performance. But right now, we don’t fully understand what those differences may be.”
Another pharmaceutical company, Merial, maker of Heartgard Plus, expressed support for the updated CAPC guidelines but downplayed resistance concerns. “Presently, there is no evidence that reduced susceptibility to macrocyclic lactones is a widespread phenomenon in the D. immitis population or will ever become one,” the company stated by email to the VIN News Service. “Further work will be needed to determine the extent to which the existence of resistant isolates will be a concern.”
In the meantime, how concerned should dog owners be about whether their dog’s heartworm preventive is effective?
Little advises that dog owners should not panic, but make sure they pay attention to maintaining a good heartworm prevention program, working in conjunction with their veterinarian. “Compliance is more important than ever before,” she said.
“What worries me,” Little continued, “is when I hear people say, “Oh, heartworm preventives — I hear those don’t work anymore.” She stressed that preventive products still work quite well for their intended function – preventing heartworm disease.
“Not every third-stage larva is resistant,” she said, referring to the infective stage in the heartworm life cycle. “It’s not uniform throughout the population, and the number of worms is correlated with the severity of disease.”
Little went on to say that because “disease severity is linked, in part, to the number of worms present in a dog,” if one or two worms escape a preventive rather than the 25 to 30 worms that may infest an un-medicated dog, “that may be a success in terms of disease prevention.”
Little pointed out that the heartworm preventive products have always been marketed as heartworm disease preventives. “And they still are. They’re just not, in some areas, complete heartworm infection preventives.”
The CAPC guidelines emphasize the need for year-round use of heartworm preventives in uninfected dogs and annual antigen testing.
One method of treating heartworm disease, using preventive products over a long period to kill adult worms, has been fingered as a suspect in the development of resistant heartworms.
A passage in the CAPC guidelines written in capital letters practically shouts the importance of using approved “adulticide” products to treat heartworm infected dogs rather than the “slow-kill” method of using macrocyclic lactone preventives to gradually treat an adult heartworm infection.
According to the American Heartworm Society, this method can take up to two years of continuous administration to clear an infection entirely.
The need to abandon the slow-kill approach was reiterated in no uncertain terms by Blagburn. He said: “We have good data to convey to veterinarians that using anything other than the available adulticide to eliminate heartworm infections can be risky. We need to avoid slow-kill in every situation if at all possible.”
The problem with using the slow-kill technique to kill adult heartworms, experts say, is this: If there are microfilariae in the infected dog that are resistant to the macrocyclic lactone drug used, those parasites will be transmitted to mosquitoes, potentially finding their way to a new dog in which to reproduce, increasing the risk to all dogs in the area.
Little repeated the prohibition against the slow-kill technique even more strongly, calling the method irresponsible given what we now know. “If we select for resistance, even in an individual dog, we put every animal in the area at risk. We just can’t do slow-kill anymore,” she said.
That’s not to blame those who used the technique previously, she added. “We didn’t know. We thought it was OK. We were trying to do in some situations what we thought was best for the dog. But it’s no longer a viable option.”
Little and Blagburn stressed that if a veterinarian believes that the slow-kill approach truly is medically indicated, the dog first must be free of circulating microfilariae. Only dogs without microfilariae should be maintained on preventives long-term, they said.
Given the preponderance of evidence of resistance presented at the veterinary parasitology meeting last month, Little said the CAPC board had no difficulty concluding that resistance is an issue.
“When we saw the data, it was confirmation,” she said. “It was very compelling because it was multiple laboratories finding the same evidence. We have very strong evidence that there has been a shift in preventive efficacy in laboratory studies that corresponds with what veterinarians have been telling us from the field.