An epidemiological study of canine filarioses in north-west Italy: What has changed in 25 years?

A field survey aimed at updating knowledge of the distribution and prevalence of filarial infections in the Piedmont region was undertaken. Blood samples were collected from 2628 dogs (10–15 dogs/100 km²) which had remained in the local area, were kept in the open overnight, were more than 2 years old and had not previously been treated with microfilaricidal drugs. Infection was diagnosed by a modified Knott test. Comparison of the results with those from a similar survey carried out 25 years ago showed a 3-fold increase in the size of the endemic area, with the colonization of new habitats, and a 4-fold increase in the prevalence of Dirofilaria immitis infection.     

Climate and Dirofilaria infection in Europe

Climatic changes, together with an increase in the movement of cats and dogs across Europe, have caused an increase in the geographical range of several vector borne parasites like Dirofilaria, and in the risk of infection for animals and humans. The present paper reviews the effects of climate and other global drivers on Dirofilaria immitis and Dirofilaria repens infections in Europe and the possible implications on the transmission and control of these mosquito-borne nematodes. In the last several years, growing degree day (GDD)-based forecast models, which use wide or local scale temperature data, have been developed to predict the occurrence and seasonality of Dirofilaria in different parts of the world. All these models are based on the fact that: there is a threshold of 14 °C below which Dirofilaria development will not proceed; and there is a requirement of 130 GDD for larvae to reach infectivity and a maximum life expectancy of 30 days for a vector mosquito. The output of these models predicts that the summer temperatures (with peaks in July) are sufficient to facilitate extrinsic incubation of Dirofilaria even at high latitudes. The global warming projected by the Intergovernmental Panel on Climate Change suggests that warm summers suitable for Dirofilaria transmission in Europe will be the rule in the future decades and if the actual trend of temperature increase continues, filarial infection should spread into previously infection-free areas. These factors not only favour incubation of Dirofilaria, but also impact on mosquito species. Recent findings have also demonstrated that Aedes albopictus is now considered to be an important, competent vector of Dirofilaria infections. This mosquito species could spread from southern to northern European countries in the near future, changing the epidemiological patterns of dirofilariosis both in humans and animals.     

Surgical Extraction of Transplanted Adult Dirofilaria immitis in Cats

A jugular venotomy technique was developed to attempt extraction of Dirofilaria immitis in cats. Seven cats were first examined by cardiac ultrasound to establish the location of adult D. immitis that had been inserted by jugular venotomy. The efficiency of an extractor catheter in surgically removing filariae similarly inserted into 13 experimental cats was then assessed. A mean extraction success rate of 96% was achieved. This technique would seem to be worthy of clinical use provided the filariae are in the right atrial area.     

An updating of the occurrence of canine heartworm disease in northern Italy

A survey was carried out in northern Italy (Veneto and Friuli Venezia Giulia Regions) to assess the extension of canine heartworm disease close to the classic hyperendemic areas of the Po Valley. A filtration test on 275 privately owned dogs showed a mean prevalence of 44%, with a peak of 55% in the Venice province. A high prevalence (17%) of occult filariosis was discovered using a serological test. These values fall within the medium-high range previously reported from other Italian areas. The provinces of Pordenone, Udine, Trieste, Treviso and Belluno, where no cases had been previously reported, were found to be infected. The distribution of the infection did not differ significantly with the dogs' origin or sex. The prevalence seemed to be influenced significantly (p<0.01) by the hosts' age, function and degree of outdoor activity, reflecting the different exposure risks.Abbreviations EDTA ethylenediaminetetraacetic acid - ELISA enzyme-linked immunosorbent assay     

Prevalence and epidemiological aspects of Dirofilaria immitis in dogs from Kayseri Province, Turkey

This study was conducted to determine the prevalence of Dirofilaria immitis infection and to investigate the risk factors related to heartworm disease in dogs from Kayseri, Turkey. Blood samples were collected from 280 dogs from May 2005 to March 2006 and were examined by membrane filtration-acid phosphatase histochemical staining and antigen Elisa techniques to detect circulating microfilariae and antigens of D. immitis, respectively. Of the total of 280 dogs, 27 were positive for D. immitis with a prevalence value of 9.6%. In addition 29.6% of positive dogs determined to have occult D. immitis infections. D. immitis was the only canine filarial parasite present in the study area. The mean number of microfilariae in infected dogs was 4730+/-5479 per ml of blood. The highest heartworm prevalence were observed in 7-10 age group (28.6%) followed by 4-6 (17.1%) and 0.5-3 (4.8%) age groups. The differences between 0.5-3 and other age groups were found significant, whereas no statistically significant difference was observed between 4-6 and 7-10 age groups. The infection was more prevalent in males, larger breeds and the dogs not on prophylaxis. No statistically significant difference was observed between stray and owned dogs. Our results suggest that heartworm treatment and prophylaxis should be considered in Kayseri Province.     

The host-parasite relationship in canine heartworm infection in a hyperendemic area of italy

From November 1990 to June 1991, 2273 Dirofilaria immitis were collected from 175 stray dogs euthanized in the province of Padua. The breed, sex, age and weight of each animal were noted. The worms were counted, sexed, differentiated as adults or fifth-stage larvae and weighed, and their length was measured.The host-parasite relationship in this epidemiological situation was characterized by a high prevalence (67%) together with a low intensity (19) and abundance (13). The frequency distribution of the parasites in the population of dogs followed a negative binomial pattern (K+0.3177), showing a good, stable host-parasite relationship. The major risk of infection was in late July and August, some new infections being established in October and, maybe, in November. The majority of dogs that acquired new infections were young animals, probably because of an immune response in older dogs. However, the prevalences increased (p<0.01) in dogs from 1 to 5 years old, in shepherd and hunting dogs compared to the other breeds, and in large as opposed to small dogs.Microfilaraemia (range 1–1 883 000/ml) correlated, as a trend, with the number of adult filariae, which also correlated with the age and the weight of the dogs (p0.01). No significant correlations were found between the length or weight of the adult filariae and the data from dogs.Abbreviations EDTA ethylenediaminetetracetic acid - L3, L4, L5 third-, fourth- and fifth-stage larvae respectively     

The validity of some haematological and elisa methods for the diagnosis of canine heartworm disease

Examinations for heartworm (Dirofilaria immitis) were performed on 175 impounded dogs from a hyperendemic area of the Po Valley (Italy). Each blood sample was used wiht five haematological diagnostic methods (filtration, direct smear, modified Knott, clotted blood and capillary tube) and three commercial ELISA kits (PetChek, Diasystems, Uni-Tec). The results were compared with the true infection status obtained from post-mortem examination of the heart, pulmonary arteries, thoracic venae cavae and lungs. The prevalence of the infection by adult worms at necropsy was 63%. The sensitivity of the tests ranged from 60% (capillary tube) to 81% (Diasystems) and the specificity from 88% (filtration) to 98% (PetChek). The results of all the tests differed significantly (p<0.01) from those obtained at necropsy. The sensitivity of the tests was also assessed with respect to the differing numbers of worms in the hosts. A positive correlation between the worm burden and the sensitivity was observed in all the tests. It is apparent that the ELISA methods were better able to detect cases with a low number of worms than the haematological tests.Abbreviations AC accuracy - CB clotted blood - CT capillary tube - DI Diasystems - DS direct smear - ELISA enzyme-linked immunosorbent assay - FI filtration - MK modified Knott - NPV negative predictive value - PE PetChek - PPV positive predictive value - SE sensitivity - SP specificity - UN Uni-Tec     

Immunohistological observations on pulmonary tissues from dogs infected withDirofilaria immitis

Pulmonary tissues from non-infected dogs, naturallyDirofilaria immitis-infected dogs and experimentally infected puppies, selectively necropsied after infection, were assessed using peroxidase-antiperoxidase (PAP) staining technology. Sequential sections of pulmonary tissue were PAP stained with anti-freshD. immitis serum, anti-paraffin processedD. immitis serum, anti-dog immunoglobulin (IgG, IgG Fc, IgM) sera and anti-dog complement (C₃) serum, and examined for antibody, complement and forD. immitis antigen. The extent of alveolar septal thickening was positively correlated with infection status. Cellular infiltration was most evident surrounding obstructed areas whereD. immitis werein situ. Antigenic material (microfilariae, eggs, fragmented filariae) labelled by PAP was identified in the pulmonary arteries, alveolar capillaries and alveolar septa. Deposits of complement and IgG, presumably associated with immune complex formation, were also observed in some of the infected dogs. Identification of antigen, antibodies and complement associated with alveolar septal pathology suggested that immune mechanisms were active in its development.Abbreviations FW fresh worm - PAP peroxidase-antiperoxidase - PW processed worm     

A retrospective study of the clinical hematology and the serum biochemistry tests made on canine dirofilariasis cases in an animal hospital population in Bangkok, Thailand

Heartworm disease, caused by the filarial nematode, Dirofilaria immitis, is a major, potentially life-threatening disease of dogs, with worldwide distribution and global significance. It is not only of veterinary importance but it also has zoonotic potential in many regions. It is considered as an endemic disease in Thailand, although clinical data about the disease is rarely reported. The objectives of this study were to characterize the clinical hematology and the biochemistry of canine dirofilariasis cases admitted to Chulalongkorn University, Small Animal Teaching Hospital in Bangkok, Thailand, from 2001-2003. All hematology and serum biochemistry parameter interpretations were based on reference values. A total of 1023 dogs were evaluated in this study. Dogs were divided into three groups based on their heartworm classification (microfilaremic, occult and negative). The major hematological findings in microfilaremic dogs were a mild to moderate anemia, mild to severe thrombocytopenia, marked leukocytosis, moderate to marked neutrophilia, eosinophilia and monocytosis. The most common serum biochemical abnormalities in microfilaremic dogs included increased alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase with a mean+/-SD of 311+/-299, 82+/-76 and 50+/-38 IU/L, respectively. It is likely that this parasitic infection led to the impairment of the hematological and biochemical status of the infected dogs. We believe that investigation of these laboratory based parameters, when associated with the clinical signs, is a very important approach to be considered in the routine clinical follow up, as well as being important for therapeutic evaluations.     

Geographical information systems as a tool in the control of heartworm infections in dogs and cats

Geospatial tools (e.g., geographical information systems, remote sensing, global positioning systems, and virtual globes) are very useful for the simultaneous visualization of health data with environmental data, which holds promise to understand environmental-health linkages and to generate new hypotheses to be tested in future research. Current epidemiological studies clearly show that the distribution patterns of vector-borne infections are changing; for example, in Europe, heartworm infection and subcutaneous dirofilariosis are spreading throughout areas that previously had little to no incidence of heartworm. In view of the changes of the distribution patterns of Dirofilaria immitis and Dirofilaria repens, geospatial tools are now more useful for mapping (including territorial sampling), monitoring, ecological analysis, risk assessment, forecasting (including the choose of the timing of treatment), early warning, and surveillance of both heartworm and subcutaneous dirofilariosis. All these issues have control of these infections as the ultimate goal.     

Pharmacological evaluation of contractile activity of the dog heartworm <Emphasis Type="Italic">Dirofilaria immitis</Emphasis>

Effects of a variety of compounds on spontaneous contractile activity of whole, intact, adult canine heartworms (HW), which had been maintained in culture, were evaluated to improve understanding of the pharmacological sensitivities of this parasitic nematode. Acetylcholine, pilocarpine, imidazole, levamisole, and DL-tetramisole caused spastic paralysis. Gamma-aminobutyrate (GABA), the GABA-mimetic muscimol, the GABA amino transferase inhibitor 3-mercaptopropionic acid, fenthion, ketamine, levodopa, and salinomycin caused flaccid paralysis. Atropine and monensin had inhibitory effects. Neostigmine, the neuromuscular blocking agents decamethonium, succinylcholine, and D-tubocurarine, and the aminergic agents epinephrine, norepinephrine, and serotonin had little or no effect on contractile activity. Thiacetarsamide had a nonreversible, slow onset, inhibitory effect on contractile activity. Occurrence of spastic or flaccid paralysis was not correlated with gender or culture age and was never associated with the same compound. Submaximal stimulatory or inhibitory responses paralleled the type of maximal responses (spastic or flaccid paralysis) for most compounds. Concentration variations producing maximal effects suggested considerable variation in individual preparation sensitivity, which did not appear to involve cuticle defects or time in culture. Difference in gender sensitivity was noted only for levamisole, which caused greater stimulation of contractile activity in males than in females.     

Genetic polymorphism in Dirofilaria immitis

Dirofilaria immitis is the causative agent of heartworm disease. Reports of macrocyclic lactone inefficacy prompted an investigation of genetic polymorphism in D. immitis. Currently, there is a lack of genetic information for this parasite. Information on baseline levels of genetic heterogeneity in the dog heartworm would have important implications for the possible development of macrocyclic lactone resistance in D. immitis. Genetic variability was investigated to assess the extent of genetic polymorphism in D. immitis populations from the USA (field and laboratory samples) and Japan (field samples). Single nucleotide polymorphisms (SNPs) were investigated in a full-length β-tubulin gene and segments of genes encoding heat shock protein 60 (Hsp60), a P-glycoprotein (Pgp), sarco-endoplasmic reticulum Ca(2+)ATPase (Serca) and phosphofructokinase (PFK). Significant differences in SNP frequencies were found in all genes except PFK. A combined genotype built from two SNPs from β-tubulin, Hsp60, Pgp and Serca was analyzed in the US lab, US field and Japan field samples. Some combined genotypes were unique to each sample group while others were shared between groups. F coefficients calculated for 15 SNPs from β-tubulin, Hsp60, Pgp and Serca were not in equilibrium. Differences in F coefficients were observed between the groups. D. immitis was found to be genetically heterogeneous. This genetic heterogeneity has implication for the development of genetically selected strains of the parasite.     

Acute death in heartworm-infected cats: unraveling the puzzle

Although the acute death syndrome in feline heartworm disease is widely recognized, its pathogenesis remains a mystery. The most widely held hypothesis is that an acute anaphylactic reaction, perhaps precipitated by the death of the parasite, is the underlying cause. This study investigated the role of the physical form of antigen (Ag) in the ensuing reaction when Dirofilaria immitis-sensitized cats are challenged by intravenous (IV) administration of heartworm Ag. Healthy D. immitis-naive cats (n = 23) were sensitized using subcutaneous injections of adjuvanted D. immitis Ag administered weekly for 6 weeks. After sensitization, cats (n = 20) were anaesthetized and challenged with IV D. immitis Ag in various forms or with IV sterile 0.9% saline (n = 3). Systolic blood pressure, respiratory rate, degree of dyspnea, blood oxygen saturation, and heart rate were measured immediately before and at 10-15 min intervals after challenge until terminal apnea occurred or until euthanasia at 140 min after challenge. Blood samples were collected for complete blood count and measurements of serum serotonin immediately before and at 10, 20, and 35 min after challenge. Clinical observations were recorded as they occurred, or at 10-15 minute intervals, whichever was the more frequent. The most severe post-challenge reactions occurred in cats challenged with Ag from dead worms, live worms, and 20 ng/mL Ag. Dyspnea increased significantly after challenge in all three groups (p < 0.001; p = 0.04, and p = 0.002, respectively), and blood oxygen saturation dropped post-challenge in the Dead Worm (p < 0.001) and the 20 ng/mL Ag (p = 0.002) groups. In the 20 ng/mL Ag group, systolic blood pressure decreased (p <0.05) and respiratory rate increased (p < 0.05) post-challenge. Clinical observations included dyspnea, gastrointestinal signs (retching, defecation, or flatulence), urination, and less commonly, hemorrhage from the nostrils or anus, or cutaneous swelling (general or specifically facial). The 20 ng/mL Ag group had the highest rate of clinical signs, followed by the Dead Worm group. The most common and reliable hematologic change associated with severe clinical effects of D. immitis Ag challenge was increased hematocrit, which was statistically higher after challenge than at baseline in the Dead Worm group (p = 0.012). The model demonstrated that the physical form of heartworm Ag used for IV challenge in D. immitis-sensitized cats is an important factor for determining the characteristics of the post-challenge reaction, and the amount of exposed internal filarial Ag presented to the feline immune system may influence the severity of the response to challenge.     

Survey of giardiosis in household and shelter dogs from metropolitan areas of Curitiba, Paraná state, Southern Brazil

Giardia duodenalis is a protozoan parasite that causes a broad range of clinical symptoms varying from none--in asymptomatic carriers--to mild recurring diarrhea consisting of soft, light-colored stools to acute severe diarrhea. In different parts of the world this parasite has raised increased interest due to its possible zoonotic transmission. Among domestic animals, dogs can play an important role in environmental contamination. As there is little information on the frequency of giardiosis in dogs from the Metropolitan Area of Curitiba-State of Paraná, Southern Brazil, the aim of the present work was to evaluate the prevalence of G. duodenalis in two dog populations (household and shelter). To attain the proposed aim, we collected fecal samples from 200 dogs and utilized three diagnostic techniques: Faust's technique (Faust et al. 1939), Benbrook's technique (1963) and polymerase chain reaction (PCR). Faust's technique presented the best results, as it was able to detect a larger number of Giardia cases. Taking Faust's technique as the standard, Benbrook's technique presented 66% sensitivity and PCR demonstrated 69% sensitivity. The shelter dog population showed a 24% occurrence of G. duodenalis while the household population showed a 9% occurrence. Other epidemiological aspects like age, sex, environmental conditions and methodological aspects are discussed in the present article.     

Molecular survey of Dirofilaria immitis and Dirofilaria repens by direct PCR for wild caught mosquitoes in the Republic of Korea

Adult mosquito collections using New Jersey light traps and Black-hole light traps were conducted to determine the potential vectors and the relative mosquito infection rates of Dirofilaria immitis and Dirofilaria repens in Gyeonggi and Gangwon Provinces, Republic of Korea, 2005. Dirofilaria spp. were confirmed by polymerase chain reaction (PCR) using species-specific primers for D. immitis and D. repens. Minimum field infection rates (MFIR) [MFIR = (number infected pools/total number of mosquitoes) x 1000] of 12 pools/2059 total number mosquitoes (5.8) and 21 pools (10.1) of the wild caught mosquitoes were positive by PCR for D. immitis and D. repens, respectively. Dual infections of both D. immitis and D. repens were detected by PCR in eight pools (3.9). Anopheles sinensis sensu lato (includes An. sinensis s.s., An. pullus, An. kleini, An. belenrae, and An. lesteri), An. sineroides, Aedes vexans nipponi, Culex pipiens and Armigeres subalbatus were found to be infected and are potential vectors of D. immitis and D. repens in Korea. Infections observed in mosquitoes represent potential health risks for domestic animal and human populations.     

Prevalence of the Dirofilaria immitis infection in dogs from Merida, Yucatan, Mexico

The aim of the present study was to estimate the prevalence of Dirofilaria immitis infection, and to examine the relationship between host factors (gender, age and breed) and D. immitis infection in dogs. The study was designed as a cross-sectional study. A total of 676 dogs were examined for D. immitis infection. Adult worms (necropsy) and blood samples were collected from all animals for diagnosis of D. immitis. Blood samples were examined using a modified Knott's and thick drop techniques. Fifty-six of 676 dogs were diagnosed infected with D. immitis. The odds of infection were 2.85 times higher in female dogs, compared to male dogs (OR = 2.85, 95% CI = 1.5-5.5, P = 0.01). In addition, the odds of infection were 2.11 times higher in > or =3 years old dogs, compared with younger dogs (OR = 2.11, 95% CI = 1.1-4.2, P = 0.03). This information is important for a better understanding of the epidemiology of D. immitis in dogs in Yucatan, Mexico.     

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

The high prevalence of heartworm infection in shelter dogs creates a dilemma for shelter managers, who frequently operate with insufficient funding, staffing, and expertise to comply with heartworm guidelines developed for owned pet dogs. The purpose of this study was to survey canine heartworm management protocols used by 504 animal sheltering agencies in the endemic states of Alabama, Florida, Georgia, and Mississippi. Open-admission shelters, which tended to be larger and more likely to perform animal control functions, were less likely (41%) to test all adult dogs than were limited-admission shelters (80%), which tended to be smaller non-profit humane agencies, and foster programs (98%) based out of private residences. Open-admission shelters were more likely to euthanize infected dogs (27%) or to release them without treatment (39%), whereas limited-admission shelters and foster programs were more likely to provide adulticide therapy (82% and 89%, respectively). Of the 319 agencies that treated infections, 44% primarily used a standard two-dose melarsomine protocol, and 35% primarily used a three-dose split-treatment melarsomine protocol. Long-term low-dose ivermectin was the most common treatment used in 22% of agencies. Open-admission shelters were less likely (35%) to provide preventive medications for all dogs than were limited-admission shelters (82%) and foster programs (97%). More agencies used preventives labeled for monthly use in dogs (60%) than ivermectin products labeled for livestock (38%). The most common reason diagnostic testing and preventive medication was not provided was cost. These results indicate a lack of protocol uniformity among agencies and insufficient resources to identify, treat, and prevent infection. Sheltering agencies and companion animal health industries should develop guidelines that are feasible for use in sheltering agencies and provide improved access to preventive and treatment strategies for management of Dirofilaria immitis.     

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.