Diagnostic, treatment, and prevention protocols for feline heartworm infection in animal sheltering agencies

Cats are at risk for heartworm infection (Dirofilaria immitis) wherever the disease is endemic in dogs. Diagnosis is more difficult in cats, and little information is available regarding effective palliative and curative treatments for infected cats. In contrast to the challenges of diagnosis and treatment, chemoprophylaxis is highly effective, and current guidelines call for preventive medications to be administered to all cats in endemic areas. The purpose of this study was to survey feline heartworm management protocols used by 400 animal shelters and foster programs in the endemic states of Alabama, Florida, Georgia, and Mississippi. Only 23% of shelters performed feline heartworm testing. The most common reasons for not testing were expense (36%), lack of treatment options for infected cats (18%), and because the agency considers heartworm infections in cats to be less important than in dogs (12%). Most agencies (69%) did not provide preventive medication to cats. Reasons included because testing was not performed (36%), expense (35%), and the perception that local heartworm risk was low (10%). When preventive was provided, feline-labeled broad-spectrum products were used more commonly (81%) than livestock products (14%). The survey also indicated that many policy decisions were based on inaccurate knowledge of feline heartworm prevalence and pathogenesis. Issues of cost, feasibility, and education prevent most Southeastern sheltering agencies from adequately protecting cats against heartworm disease. Practical guidelines tailored to the needs of these agencies should be developed. Subsidized testing and preventive products may facilitate implementation of feline heartworm management protocols in sheltering agencies.     

Evaluation of lung pathology in Dirofilaria immitis-experimentally infected dogs treated with doxycycline or a combination of doxycycline and ivermectin before administration of melarsomine dihydrochloride

Adulticide therapy in heartworm (Dirofilaria immitis)-infected dogs can lead to thromboembolism, which can seriously compromise post-treatment health status. Lung pathology following adulticide therapy was evaluated in three groups of experimentally infected dogs. Group 1 was treated with doxycycline at 20 mg/kg per os once daily for 30 days post infection followed by an intramuscular injection of melarsomine dihydrochloride (2.5 mg/kg) at Week 12, followed 1 month later by two injections 24 h apart. Group 2 was treated as described for Group 1, with the addition of ivermectin at 6 mcg/kg given monthly per os for 24 weeks post-infection. Group 3 received melarsomine alone, as described above. All dogs were necropsied at Week 24 and lung pathology was evaluated. Lesion criteria included perivascular inflammation and endothelial proliferation. Lesions were scored by two independent pathologists who were blinded as to treatment. Results indicate that doxycycline treatment alone or combined with ivermectin had lower lesion scores than lungs from dogs who had received melarsomine alone. Dogs that received the combined doxycycline/ivermectin protocol and treated with adulticide showed less severe arterial lesions and the virtual absence of thrombi.     

Wolbachia and its influence on the pathology and immunology of Dirofilaria immitis infection

Since the definitive identification in 1995 of the bacterial endosymbiont Wolbachia that resides in different tissues of the filarial worm Dirofilaria immitis, there has been increasing interest to understand whether and what role it plays in the pathogenesis of and immune response to heartworm infection. The present study evaluated the effects of treatments on lung pathology in 20 beagle dogs experimentally infected with D. immitis. Dogs in Group 1 were treated with doxycycline (10 mg/kg/day) orally from weeks 0-6, 10-12, 16-18, 22-26, and 28-34. Dogs in Group 2 served as infected, non-treated controls. Dogs in Group 3 were given doxycycline as described for Group 1 combined with weekly oral doses of ivermectin (6 mcg/kg) for 34 weeks and intramuscular (IM) melarsomine (2.5 mg/kg) at week 24, followed by two additional melarsomine injections 24h apart 1 month later. Group 4 received only melarsomine as described for Group 3. Lung lesion criteria, scored by two independent blinded pathologists, included perivascular inflammation and endothelial proliferation. Doxycycline treatment alone had no effect on lesion scores, whereas the combination of doxycycline and ivermectin resulted in less severe perivascular inflammation. All lungs were evaluated for positive immunostaining for the Wolbachia surface protein (WSP). Control dogs showed numerous thrombi, intense perivascular and interstitial inflammation and, occasionally, positive staining for WSP. Interestingly, dogs receiving doxycycline/ivermectin/melarsomine showed significantly less severe arterial lesions and the virtual absence of thrombi.     

Molecular epidemiology of feline bordetellosis in two animal shelters in California,USA

"Kennel cough" in dogs in animal shelters is readily transmissible, reduces adoption rates, and commonly leads to the euthanasia of affected dogs. In cats, tracheobronchitis, conjunctivitis, and pneumonia have been associated with Bordetella bronchiseptica infection-but most cases of upper-respiratory infection (URI) probably are caused by herpesvirus and calicivirus, and many B. bronchiseptica culture-positive cats are clinically normal. Our prospective observational study was undertaken to document the contribution of B. bronchiseptica to disease in cats and dogs from two animal shelters undergoing outbreaks of canine kennel cough, to evaluate whether cross-species transmission might have occurred, and to determine if the presence of infected cats represented a risk to dogs. Clinically defined cases of kennel cough in dogs and URI in cats were investigated in two shelters by calculating clinical-disease incidence, alveolar-lavage cytological examination, bacterial and viral cultures, antibiotic-susceptibility testing, and molecular fingerprinting by pulsed-field gel electrophoresis.In a 40-cat and 40-dog "no-kill" shelter, the prevalences of culture positivity were 47% for B. bronchiseptica and 36% for calicivirus at the same time as two resident dogs demonstrated clinical cough. When no dogs had kennel cough 3 months later, 10% of cats were B. bronchiseptica-culture-positive and 63% calicivirus positive. In a large traditional shelter, the incidence of kennel cough in dogs increased over 12 weeks to a maximum of 19 cases/week/120 dogs, during which time the culture prevalence was 23% for B. bronchiseptica in dogs and 47% in cats. Three to 6 months before the kennel-cough epidemic, no dogs or cats were B. bronchiseptica positive. Very little genetic variability was detected in isolates from these shelters; all isolates except one corresponded to a single strain type which was identical to the pattern in a vaccine used in these shelters. Isolates from other cats, a horse, a llama, and a sea otter were genetically distinct from the shelter isolates. There was widespread resistance to cephalosporins and ampicillin, but low or no resistance to amoxicillin/clavulanate, trimethoprim-sulfamethoxazole, tetracycline, and enrofloxacin. Greater percent resistance was observed in the traditional shelter than in the no-kill shelter and feline isolates were more likely to be resistant than canine isolates.     

Heartworm and Wolbachia: therapeutic implications

A safer, more effective adulticidal treatment and a safe method for reducing microfilaremia and breaking transmission of heartworm disease early in the treatment are needed. The present study evaluated efficacy of ivermectin (IVM) and doxycycline (DOXY) alone or together (with or without melarsomine [MEL]) in dogs with induced adult heartworm infection and assessed the ability of microfilariae from DOXY-treated dogs to develop to L3 in Aedes aegypti mosquitoes and subsequently to become reproductive adults in dogs. Thirty beagles were each infected with 16 adult heartworms by intravenous transplantation. Six weeks later, dogs were ranked by microfilarial count and randomly allocated to 6 groups of 5 dogs each. Beginning on Day 0, Group 1 received IVM (6 mcg/kg) weekly for 36 weeks. Group 2 received DOXY (10 mcg/(kgday)) orally Weeks 1-6, 10-11, 16-17, 22-25, and 28-33. Groups 3 and 5 received IVM and DOXY according to doses and schedules used for Groups 1 and 2. At Week 24, Groups 3 and 4 received an intramuscular injection of MEL (2.5 mg/kg), followed 1 month later by two injections 24h apart. Group 6 was not treated. Blood samples were collected for periodic microfilaria counts and antigen (Ag) testing (and later immunologic evaluation and molecular biology procedures). Radiographic and physical examinations, hematology/clinical chemistry testing, and urinalysis were done before infection, before Day 0, and periodically during the treatment period. At 36 weeks, the dogs were euthanized and necropsied for worm recovery, collection of lung, liver, kidney, and spleen samples for examination by immunohistochemistry and conventional histological methods. All dogs treated with IVM + DOXY (with or without MEL) were amicrofilaremic after Week 9. Microfilarial counts gradually decreased in dogs treated with IVM or DOXY, but most had a few microfilariae at necropsy. Microfilarial counts for dogs treated only with MEL were similar to those for controls. Antigen test scores gradually decreased with IVM + DOXY (with or without MEL) and after MEL. Antigen scores for IVM or DOXY alone were similar to controls throughout the study. Reduction of adult worms was 20.3% for IVM, 8.7% for DOXY, 92.8% for IVM + DOXY + MEL, 100% for MEL, and 78.3% for IVM + DOXY. Mosquitoes that fed on blood from DOXY-treated dogs had L3 normal in appearance but were not infective for dogs. Preliminary observations suggest that administration of DOXY+IVM for several months prior to (or without) MEL will eliminate adult HW with less potential for severe thromboembolism than MEL alone.     

Attributes, knowledge, beliefs, and behaviors relating to prevention of heartworm in dogs among members of a national hunting dog club

The Food and Drug Administration Center for Veterinary Medicine (FDA/CVM) has cited an increasing number of reports of failure of heartworm prophylaxis in dogs. Failures may be due to resistance of L(3)-L(4) stage Dirofilaria immitis to the macrocyclic lactone class of compounds used for prophylaxis, lack of compliance with and understanding of administration of prophylactics, individual differences in drug absorption or metabolism, or a combination of these factors. Using the latest scientific information, the American Heartworm Society (AHS) and Companion Animal Parasite Council (CAPC) have developed guidelines for the diagnosis, prevention, and treatment of heartworm infection in dogs. This study summarizes the knowledge, beliefs, and behaviors relating to prevention of heartworm among members of a national hunting dog club, visitors to the club website, and attendees at club-sponsored events. These factors can have a direct effect on the success of heartworm prophylaxis. Results suggest that the dog owners lack confidence in the accuracy of the heartworm test to identify infection, the efficacy of products sold for prevention of heartworm, and the effectiveness of treatment to eliminate adult heartworms from infected dogs. Knowledge about when to begin heartworm preventive medication in a new puppy and the timing of heartworm tests was also lacking among a substantial number of respondents. In order to increase acceptance of prophylaxis and reduce the likelihood of a false conclusion of prophylactic failure, education of dog owners should focus on the need for an appropriately timed annual heartworm test and the importance of administering the last dose of monthly heartworm preventative after the last possible day of potential transmission.     

Evaluation of a covered-rod silicone implant containing ivermectin for long-term prevention of heartworm infection in dogs

OBJECTIVE: To evaluate use of covered-rod (CR) silicone implants containing ivermectin for long-term prevention of infection with Dirofilaria immitisin dogs. ANIMALS: 145 adult male and female dogs. PROCEDURES: Dogs received implants of different sizes, and ivermectin concentrations and serum ivermectin concentrations were monitored for 16, 57, and 56 weeks, respectively, in 3 preclinical dose selection studies. Ability of implants to prevent infection with D immitis was evaluated in 2 further studies; dogs were challenged with 50 infective third-stage larvae 52 weeks after implant administration and necropsied 145 days after challenge, and the total number of adult heartworms was counted. A field study was then undertaken in which client-owned dogs received an implant and plasma samples were collected at intervals until week 52 for ivermectin analysis and heartworm antigen determination. RESULTS: Use of the implants resulted in maintenance of an ivermectin concentration > or = 0.2 ng/mL for 12 months. In challenge studies, no treated dogs had adult heartworms, in contrast to untreated dogs, which all had adult heartworms at necropsy. In the field study, dogs treated with an implant had negative results of heartworm antigen testing for 12 months. CONCLUSIONS AND CLINICAL RELEVANCE: The CR silicone implant containing 7.3 mg of ivermectin was 100% effective in preventing experimental infection with D immitislarvae and resulted in negative results for heartworm antigen in a field trial. This product has the potential to alleviate poor owner compliance with monthly prevention regimens.     

Evaluation of Faecal Salmonella Shedding Among Dogs at Seven Animal Shelters across Texas

Estimates of prevalence of faecal Salmonella shedding among dogs in the United States have varied widely. Surveillance among shelter dogs has been limited, although dogs in animal shelters may be at elevated risk of Salmonella infection because of their previous exposure history as well as factors inherent to shelter environments. Our objectives were to estimate the prevalence of Salmonella shedding among shelter dogs across Texas, to identify risk factors for shedding and to characterize the isolates. Using a repeated cross‐sectional study design, we collected faecal samples from dogs on two or three visits to each of seven Texas animal shelters between May 2013 and December 2014. Standard bacteriologic culture methods were used to isolate Salmonella from samples, and isolates were characterized via serotyping and anti‐microbial susceptibility testing. The prevalence of faecal Salmonella shedding among sampled dogs was 4.9% (27/554), and within‐shelter prevalence ranged from 1.9% to 8.3%. There was a marginal association (P = 0.09) between watery faecal samples and positive Salmonella status, as estimated by a logistic regression model that controlled for shelter as a random effect. However, over 60% of Salmonella‐positive dogs had grossly normal faeces. Salmonella prevalence did not vary significantly by age group or sex. The most common serovars were Newport (22%) and Javiana (15%), both of which were widespread among shelters. Resistance to anti‐microbial agents was uncommon. The prevalence of faecal Salmonella shedding among shelter dogs in Texas appears to be comparable to that seen among pet dogs in general.     

Long-term delivery of ivermectin by use of poly(D,L-lactic-co-glycolic)acid microparticles in dogs

OBJECTIVE: To evaluate the potential utility of poly(D,L-lactic-co-glycolic)acid (PLGA) as a long-acting biodegradable drug delivery matrix for ivermectin used in the prevention of heartworm disease in dogs. ANIMALS: 30 adult female dogs. PROCEDURE: Microparticle formulations containing 25 weight percent (wt%), 35 wt%, and 50 wt% ivermectin were prepared by an oil-in-water emulsion technique with solvent extraction into excess water. A fourth formulation, consisting of a mixture of 15 wt% and 50 wt% ivermectin microparticles, was blended in a 1:1 ratio to result in a 32.5 wt% ivermectin formulation. Formulations were administered once on Day 0 to groups of 6 dogs at a dose of 0.5 mg of ivermectin/kg, s.c. Half of the dogs in each treatment group and 3 untreated control dogs were infected with Dirofilaria immitis larvae 121 and 170 days after treatment. Six months after infection, dogs were euthanatized and necropsies were performed. Pharmacokinetics and efficacy were investigated. RESULTS: Analysis of pharmacokinetic data revealed sustained release of ivermectin during at least 287 days in 3 distinct phases: a small initial peak, followed by release of drug through diffusion, and polymer degradation. Untreated control dogs were all infected with heartworms. Heartworms were not found in any of the dogs in the ivermectin-PLGA treated groups. Adverse clinical signs were not observed. CONCLUSIONS AND CLINICAL RELEVANCE: All formulations were 100% effective in preventing development of adult heartworms. Results indicate that PLGA microparticles are a promising drug delivery matrix for use with ivermectin for the prevention of heartworm disease for at least 6 months after treatment.     

Factors associated with rabies vaccination of dog shelter staff in the United States

US animal shelters house and care for dogs with unknown medical histories. Such unknown medical backgrounds pose concern for zoonotic transmission of diseases to the shelter staff. One important zoonotic exposure is to rabies virus which is almost always fatal after the onset of symptoms. The objective of this study was to identify the characteristics of dog shelters associated with the probability that the shelter had a policy to vaccinate shelter personnel against rabies. Five states with an established shelter registry were selected from each geographic region of the United States. A list of shelters within those states was developed from the registry list, through Internet searches and comparisons with other known lists. At least two forms of direct communication were used to ensure that humane organizations met the study definition of a dog shelter. In total, 342 of 461 (73%) shelters that met the study definition were visited by a team of students. Forty‐two of 332 (13%) shelters responding to the question required staff to be vaccinated against rabies. Logistic regression was utilized to test shelter characteristics for association with the probability that they have a rabies vaccination policy for shelter staff. Municipally funded shelters were more likely to vaccinate staff for rabies than shelters funded privately (OR = 3.0, 95% CI = 1.40–6.39). These results demonstrate that shelter funding source may influence rabies control programmes in shelters.     

Percutaneous heartworm removal from dogs with severe heart worm (Dirofilaria immitis) infestation

Canine heart worm disease is often life-threatening due to its various complications, including right side heart failure, caval syndrome and pulmonary eosinophilic granulomatosis. Several preventive medications and melarsomine have been developed and they are very effective to control heartworm infestation. However, in a case of severe infestation, melarsomine therapy often results in an unfavorable outcome because of the severe immune reaction caused by rapid killing of the adult worm. Surgical removal and an interventional method using flexible alligator forceps have been well described in the literature. Despite the usefulness of mechanical removal using flexible alligator forceps, the methodology still needs to be upgraded for increasing the applicability for treating dogs with severe infestation. We describe herein a newly developed percutaneous removal method for heartworms and this was successfully applied to 4 dogs with severe heartworm infestation. The follow-up studies also showed favorable outcomes with no complications.     

A needs-assessment and demographic survey of infection-control and disease awareness in western US animal shelters

A cross-sectional needs-assessment survey was used to characterize animal shelters in a 6-state region in the western US and describe infection-control practices and disease awareness. Survey questions focused on shelter demographics, infection-control practices and policies, awareness and concern over infectious and zoonotic diseases, staff and volunteer training relating to infection-control and disease awareness, use of diagnostic tools, and isolation procedures and protocols. Fifty percent of shelters responded to the survey and represented a wide variety of shelter types, sizes and locations. The top-three diseases of concern to shelters were feline upper respiratory disease (FURD), canine parvovirus and ringworm. Concern over these diseases was greater in open-admission shelters (compared to limited admission or no-kill/sanctuary) (OR 3.7, 95% CI 1.1-12.5) and in shelters with a desire for more zoonotic-disease training (OR=6.1, 95% CI 1.5-24.8) (compared to shelters desiring infectious-disease training, training on cleaning and disinfection or those who have no need for further training). In 45% of responding shelters many to most animals arrive with infectious diseases. Written protocols for preventive medicine exist in 88% of shelters, cleaning and disinfection protocols in 75%, specific disease protocols for outbreak situations in 36% and infection-control manuals in 15%. Veterinarians are in charge of infection-control in 6% of shelters. Approximately 45% of shelters vaccinate dogs and cats for rabies. Infectious-disease training is provided to 30% of staff and 35% of volunteers upon hire. Overall, volunteers received less training in infectious- and zoonotic-disease identification, prevention and control than staff members. Ninety percent of shelters said they would benefit from training in infectious and zoonotic disease. Results from this study can be used to assess and address needs in animal shelters relating to infection-control, infectious and zoonotic-disease awareness and can help guide development of shelter staff and volunteer training.     

Dirofilaria immitis: worm burden and pulmonary artery proliferation in dogs from Michigan (United States)

Despite the ability to prevent heartworm disease, infection with Dirofilaria immitis continues to be a major problem for domestic dogs. To determine worm burden in heartworm-positive dogs from three county animal shelters in the state of Michigan in the United States and to assess the relationship between gross intimal proliferation and worm burden, necropsy was done on 176 heartworm-positive dogs. Adult heartworms were found in the heart and pulmonary artery of 170 of the 176 (96.6%) dogs examined. Mean worm burden was 14 +/- 13 (range 0-85). Fifty-nine percent of dogs had < or =10 heartworms. In contrast, 52% of dogs in a published report from the southern US (Florida) had worm burdens >10 [C.H. Courtney, Q.Y. Zeng, The structure of heartworm populations in dogs and cats in Florida, in: Proceedings of the American Heartworm Symposium, 1989]. These data suggest that mean worm burden in northern areas may be < or = that in warmer areas. Also, since diagnostic tests are less sensitive with lower worm burdens, diagnosis of heartworm infection in Michigan and other surrounding more northern states may be a greater challenge than in areas with higher worm burdens.     

The safety-net story about macrocyclic lactone heartworm preventives: a review, an update, and recommendations

A number of safe, effective, and convenient heartworm preventatives are currently available for virtually all canine and feline pets. Yet, a 2001 survey of over 18,000 veterinary clinics in the United States identified more than 240,000 dogs and 3000 cats infected with Dirofilaria immitis. This high level of owner compliance failure is alarming. Prolonged administration of some of the macrocyclic lactone (ML) preventatives kills young larvae, older larvae, "immatures," young adults, and/or old adults. Efficacy of 95% or more requires dosing for 9-30 months, with older worms being more difficult to kill. Of the various MLs, ivermectin (IVM) has the most potent safety-net and adulticidal activity, milbemycin oxime has the least, and selamectin and moxidectin injectable lie somewhere in between. The unique effects of IVM are related to the age of the heartworms at initiation of treatment. The earlier treatment is started, the more stunted and smaller the worms and the shorter their survival time. Conversely, the later treatment is started, the longer the worms live, and the more likely the dog will be antigen- and microfilariae-positive. Drug effects do not appear to be enhanced by increasing the dosage or administering at shorter intervals, and it appears that continuous monthly treatment is needed to produce the full effects of the drug. The American Heartworm Society (AHS) recognizes the safety-net (or reach-back effect) and adulticidal properties of some MLs, particularly IVM. The AHS 2003 (American Heartworm Society, 2004. 2003 Updated guidelines for the diagnosis, prevention, and management of heartworm (Dirofilaria immitis) infection in dogs. In: McCall, et al., (Eds.), Proceedings of the Symposium Session on Recent Advances in Heartworm Disease, The 19th International Conference of the World Association for the Advancement of Veterinary Parasitology, New Orleans, LA, 10-14 August, 2003. Vet. Parasitol. 125, 105-130) canine guidelines state that it is beneficial to administer prophylactic doses of IVM before treatment with melarsomine. Results of laboratory studies suggest that less active dogs are at low risk of severe thromboembolism and death. However, heartworm-positive working dogs might be more at risk. Worsened radiographic and echocardiographic images in a client-owned dog given IVM monthly for 2 years with greatly restricted exercise suggests that such treatment of dogs with clinical, radiographic, and/or echocardiographic evidence of heartworm disease as well as for asymptomatic working dogs is contraindicated. Furthermore, until further data are available, such treatment of even the less active asymptomatic dog should be administered only with much caution and with examination by a veterinarian at least once every 4-6 months. IVM clearly provides potent "safety-net" activity against older larvae, immatures, and young adults in cases of owner compliance failure, even when the owner and veterinarian are not aware that the animal is infected, and offers much promise as a unique "soft-kill" treatment for young, and possibly older adult heartworms, with reduced risks.     

Determinants of adoption and euthanasia of shelter dogs spayed or neutered in the university of california veterinary student surgery program compared to other shelter dogs

Limited economic resources and pet overpopulation force animals shelters to consider euthanasia of adoptable animals every day. Veterinary medical schools can play a positive role in increasing pet adoption and combating overpopulation by providing free neutering for shelter animals. This retrospective cohort study illustrated that the cooperative efforts of a veterinary medicine surgical teaching program and local animal shelters decreases euthanasia of adoptable pets. At the University of California, Davis (UCD), shelter dogs are neutered by veterinary students and then returned to the shelter for adoption. The rates of adoption and euthanasia of the dogs neutered at UCD were contrasted with a comparison shelter group to determine the effect of pre-adoption neutering. The UCD-neutered dogs had a lower rate of euthanasia than the comparison shelter group at the shelters investigated. At Sacramento County Animal Care and Regulation, 73% of the UCD group but only 36% of the comparison group were adopted. At Yolo County Animal Services, 71% of the UCD group and 45% of the comparison group were adopted. The sex of an animal did not significantly affect the rate of euthanasia. Dogs that were predominantly pit bull, rottweiler, or chow chow breeds had higher rates of euthanasia than other breeds, independent of neuter status. Also, juveniles (less than one year old) had lower rates of euthanasia than adults, independent of neuter status. UCD adult dogs had lower rates of euthanasia than comparison adults. Post-surgical UCD dogs spent a longer average time in the shelter before adoption (15 days at Sacramento; 16 days at Yolo) than the comparison dogs (11 and 12 days, respectively). UCD dogs also spent a longer average time in the shelter before euthanasia (18 and 25 days, respectively) than the comparison dogs (13 days at both shelters). Lower probabilities of euthanasia for behavioral or medical reasons were found for UCD dogs than for the comparison dogs. The probability of euthanasia for reasons of space limitations increased with time in shelter for both groups. In this study, pre-adoption neutering increased adoptions without increasing the probability of medical or behavioral euthanasia.     

Epidemiology of heartworm: what is happening in South America and Mexico?

Canine heartworm has been known to exist in the Americas for more than 150 years (1847), and the first South American report was published approximately 30 years later (1875). The first human case was reported in 1887 and the first feline case in 1921. Coincidently, these two reports were from Brazil, where most surveys of the disease during the past two decades have been conducted in dogs. Feline cases are seldom found in the South American literature, although feline heartworm disease has been reported in Venezuela and Brazil. The prevalence in Mexico seems to be stable over the past 10 years (7.3-7.5%). Only 5 of the 13 South American countries have reported on canine heartworm infection prevalence. In Argentina, the national prevalence ranges from 3.5 to 12.7%; however, there was a much higher prevalence (17.7 and 23.5%) reported for two sections of Buenos Aires. In Lima, Peru, the prevalence is 4.35%, and Colombia reports 3.8-4.8% of dogs are infected. No infections were detected in 1056 dogs sampled in Chile. In Brazil, the national prevalence has declined from 7.9% in 1988 to 2% in 2001. The downward trend observed for canine heartworm in Brazil suggests that multiple pressures may be affecting the nematode transmission, including a possible decrease in mosquito vector population due to better control programs, reduction of transmission due to effective chemoprophylaxis, reduction of microfilaremic dog populations with the off-label use of injectable ivermectin, or reduction of the reproductive capacity of worms from tetracyclines used to control ehrlichiosis. Survey of a large population of captured mosquitoes indicated the most frequent species captured were vectors of heartworms (Aedes taeniorhynchus (73.9%), Aedes scapularis (20%) and Culex quinquefasciatus (2.5%), suggesting that the composition of the mosquito population is not a critical factor in the decrease in heartworm infections in dogs in South America.     

Epidemiologic evaluation of multiple respiratory pathogens in cats in animal shelters

Upper respiratory tract infection (URI) propagates readily within cats in shelters and often results in euthanasia of affected cats. In a case-control evaluation of 573 cats in eight shelters in California in 2001 and 2002, the prevalence of feline calicivirus (FCV) was from 13 to 36%, feline herpesvirus (FHV) was from 3 to 38%, and prevalence of Bordetella bronchiseptica, Chlamydophila felis, and Mycoplasma species was from 2 to 14%. Cats with URI tended to be housed in isolation, dehydrated, and younger than cats without URI, and infected with FHV, Mycoplasma species, FCV, or C felis. Shelters differed in the prevalence of pathogens and many cats appeared positive for infection after about 1 week of sheltering. It is helpful for shelters to understand the risk factors associated with URI in order to evaluate the costs and benefits of treatment and improve their procedures to decrease the incidence of URI within their facilities. Antiherpetics and antimycoplasmal drugs may be beneficial for individual animal care. Results document the utility of comprehensive URI surveillance and herd management for specific pathogens typical in that shelter.     

Efficacy of ivermectin and pyrantel pamoate combined in a chewable formulation against heartworm, hookworm, and ascarid infections in dogs.

Eight trials were conducted in dogs to document the efficacy of ivermectin (6 micrograms/kg of body weight) and pyrantel pamoate (5 mg of active pyrantel/kg) in a beef-based chewable formulation against Dirofilaria immitis, Ancylostoma caninum, Uncinaria stenocephala, Toxocara canis, and Toxascaris leonina. Three studies involved induced infection with D immitis, and 5 studies involved induced or natural infection with hookworms and ascarids. In 3 intestinal parasite trials, the efficacy of the combination chewable tablet was compared with each of its components. Results indicated that 1 component did not interfere with the activity of the other. In 1 heartworm and 2 intestinal parasite trials, the efficacy of pyrantel, ivermectin/pyrantel combination, or ivermectin with pyrantel dosage of 10 mg/kg was evaluated. The ivermectin/pyrantel combination was 100% effective in preventing development of D immitis larvae. Efficacy of the combined product against T canis, Toxascaris leonina, A caninum, and U stenocephala was 90.1, 99.2, 98.5, and 98.7%, respectively. In the intestinal parasite trials, each individual component was found not to interfere with the anthelmintic action of the other. Increasing the dosage of pyrantel to 10 mg/kg (2 x that in the combination) did not interfere with the efficacy of ivermectin against heartworm or increase the activity of pyrantel against intestinal parasites.     

Can heartworm prevalence in dogs be used as provisional data for assessing the prevalence of the infection in cats?

Cats are considered a susceptible host for Dirofilaria immitis; however, increased host resistance is reflected by relatively low adult worm burdens in natural and experimental infections; the prolonged prepatent period (8 months); the low level and short duration of microfilaremia; and the short life span of adult worms (2-3 years). From April to September 2006, 212 cats and 608 dogs, all exposed for at least one transmission season, were screened for D. immitis infection in a multi-center study in the Po River Valley in northern Italy. Cats were initially evaluated by antibody testing; positive subjects were followed up by antigen testing and echocardiography (and necropsy if death occurred). The prevalence in dogs was 29% by a modified Knott test and antigen testing compared with a prevalence of 4.7% in cats by an antibody test; six of these infections (2.8%) were confirmed by the follow-up evaluations. This field study demonstrated that the prevalence of heartworm infection in cats in this area is within the expected limits of 9-18% of the prevalence in dogs. Antibody testing likely underestimates the real prevalence of D. immitis infection in cats. These results also emphasize the importance of preventive treatment in cats.     

Possible application of oxidative stress parameters for the evaluation of animal welfare in sheltered dogs subjected to different environmental and health conditions

The objective of this study was to establish an additional prognostic parameter to assess animal welfare. We explored the validity of using the thiol antioxidant barrier (SHp) and determination of reactive oxygen metabolites (dROMs) as indicators of stress and welfare in sheltered dogs. The shelter is a stressful environment for a dog because of its unpredictable and uncontrollable nature. The dogs enrolled in the present study belonged to 2 types of animal shelters (shelter 1 and shelter 2) that differed for social and spatial restrictions for the dogs. Animals were tested for leishmaniosis and ehrlichiosis and divided into 4 groups on the basis of their negative (group A and B) or positive (group C and D) status and the shelter they belonged to. The Student t test showed significant differences on SHp concentrations between groups A and B (negative titers; different shelters) (P < 0.0001; t₍₁₀₎ = 11.08), groups C and D (positive titers; different shelters) (P < 0.02; t₍₇₎ = 2.998), and groups A and C (different infection status and same shelter) (P < 0.004; t₍₈₎ = 3.975). Levels of dROMs showed significant differences between groups A and C (different infection status and same shelter) (P < 0.03; t₍₈₎ = 2.552) and groups B and D (different infection status and same shelter) (P < 0.02; t₍₉₎ = 2.817). The high dROMs values recorded in all dogs during the study may be because of the stressful environment of animal shelters, in general. The low SHp concentrations that we found in dogs from shelter 1 may suggest a highly stressful condition related to the poor social environment for interaction. SHp and dROMs may provide useful information about the responsiveness of sheltered dogs subjected to different environmental (social and spatial restrictions, management practices, and diet) and health (negative or positive status for leishmaniosis and ehrlichiosis) conditions and may suggest the possibility of establishing an additional prognostic tool for the assessment of welfare and health in sheltered dogs.