Human ocular infection with Dirofilaria repens (Railliet and Henry, 1911) in an area endemic for canine dirofilariasis.

Dirofilaria repens, which is usually found in canine subcutaneous tissues, is the main causative agent of human dirofilariasis in the Old Word. However, a relationship between animal and human cases of dirofilariasis caused by D. repens in a given area has never been demonstrated. The uneven distribution of D. repens in provinces in Sicily, Italy represented the foundation for this study. We report a human case of ocular infection with D. repens from Trapani Province, where canine dirofilariasis is endemic. The nematode was morphologically and molecularly identified and surgical removal of the parasite was documented. The relationship between the prevalence of D. repens in dogs and the occurrence of human cases of ocular dirofilariasis is discussed on the basis of a review of the historical literature.

Changing climate and changing vector-borne disease distribution: the example of Dirofilaria in Europe.

Climatic changes, together with an increase in the movement of dogs across Europe, have caused an increase in the geographical range of Dirofilaria infections. The present paper is focuses on northeastern European countries, where survey data have shown an increase of Dirofilaria repens infections both in animals and humans. A growing degree day-based forecast model has been developed to predict the occurrence. The model is based on evidence that there is a threshold of 14 °C below which Dirofilaria development will not proceed in mosquitoes, there is a requirement of 130 growing degree-days (GDDs) for larvae to reach infectivity, and there is a maximum life expectancy of 30 days for a mosquito vector. The output of this model predicted that the summer temperatures (with peaks in August) are sufficient to facilitate extrinsic incubation of Dirofilaria even at latitudes of 56 °N and longitudes of 39 °E. Despite the fact that both Dirofilaria immitis and D. repens have the same temperature requirement for extrinsic incubation in mosquitoes, empirical data has shown that D. repens is the main cause of dirofilarial infections in both humans and animals. Clinical signs are absent in most canine infections with D. repens. Furthermore, diagnosis is problematic and in-clinic serological tests, such as those for D. immitis, do not exist. Therefore, most infections go undiagnosed, allowing the infection to spread undetected.

Efficacy of moxidectin microsphere sustained release formulation for the prevention of subcutaneous filarial (Dirofilaria repens) infection in dogs.

A study was carried out to assess the efficacy of a moxidectin microsphere sustained release (SR) injectable formulation (Guardian SR Iniettabile, Fort Dodge) for the prevention of Dirofilaria repens infection in experimentally infected dogs. On day 0, 18 Beagle dogs, 9 male dogs and 9 female dogs, weighing 12-16 kg were ranked in ascending order of body weight (b.w.) and blocked into pairs. Within each pair, dogs were allocated to Group 1 or Group 2 at random. On the same day, dogs in Group 1 were injected with 0.05 ml/kg b.w. of saline solution and dogs in Group 2 were injected with moxidectin SR at the label dose 0.17 mg/kg b.w. (0.05 ml/kg b.w.). Six months after moxidectin SR or saline injection, on day 180, each dog in the two groups was challenged with 50 infective larvae of D. repens collected from laboratory-reared, experimentally infected Aedes aegypti. Dogs were humanely euthanized on day 380 of the study, approximately 7 months from D. repens challenge. At necropsy, no worms were found in dogs treated with moxidectin SR (Group 2) while adult worms were found in saline-treated dogs (total 90; 38 males and 52 females; arithmetic mean 10, standard error 0.96, median 9, range 7-15) (Group 1 vs Group 2 P<0.001). In this experimental study, moxidectin SR injectable showed full efficacy (100%) lasting at least 6 months, and is able to prevent subcutaneous D. repens patent infection throughout the entire transmission season in Europe.

Right atriotomy using total venous inflow occlusion for removal of heartworms in a cat.

Heartworm infection with caval syndrome was detected in a thirteen-year-old male cat. However, removal of the heartworms via a jugular venotomy was infeasible because the size of the jugular vein limited our ability to use flexible alligator forceps. Therefore, a right atriotomy using total venous inflow occlusion was performed to remove the heartworms. The procedure was accomplished successfully, and the cat recovered from its symptoms. The present case suggests that right atriotomy using venous inflow occlusion is practical for removal and prevention of rupture of heartworms.

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 degrees 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.

Myocardial fluid balance in dogs with naturally acquired heartworm infection.

OBJECTIVE: To determine the effect of naturally acquired heartworm (Dirofilaria immitis) infection on myocardial fluid balance as indicated by myocardial water content and the dynamics of transepicardial fluid flow. ANIMALS: 7 dogs infected with adult heartworms and 8 dogs free of heartworm infection. PROCEDURES: Infected dogs had heartworms in the right ventricle, pulmonary artery, or both but no evidence of cardiovascular disease on physical examination. A hemispheric capsule was attached to the epicardial surface of all dogs for determination of transepicardial fluid dynamics and permeability of the epicardium to water and protein. Myocardial water content and hydroxyproline content were assessed at necropsy. RESULTS: Myocardial water content was significantly lower in heartworm-infected dogs. No differences in myocardial hydroxyproline content, transepicardial fluid flow, or epicardial water or protein permeability were detected. CONCLUSIONS AND CLINICAL RELEVANCE: Heartworm infection significantly altered myocardial fluid balance in dogs, possibly because of a change in the myocardial interstitial pressure-volume relationship. These changes may be associated with increased vulnerability to cardiovascular stressors in heartworm-infected dogs.

Scanning electron microscopy of vascular corrosion casts and histologic examination of pulmonary microvasculature in dogs with dirofilariosis.

OBJECTIVE: To characterize structural changes in pulmonary vessels of dogs with dirofilariosis. ANIMALS: 8 dogs with dirofilariosis and 2 unaffected control dogs. PROCEDURE: Pulmonary artery pressure was measured in affected dogs, and dogs then were euthanatized. Scanning electron microscopy was used to examine vascular corrosion casts of pulmonary vasculature. Tissue sections of pulmonary vasculature were evaluated by use of histologic examination. RESULTS: Pulmonary artery pressure was higher in dogs with severely affected pulmonary vessels. In tissue sections, dilatation, as well as lesions in the tunica intima and proliferative lesions resulting in constriction or obstruction, were frequently observed in branches of the pulmonary artery. Numerous dilated bronchial arteries were observed around affected pulmonary arteries. Hyperplastic venous sphincters were observed in small pulmonary veins and venules. In corrosion casts, affected pulmonary lobar arteries had dilatation, pruning, abnormal tapering, constriction, and obstruction. In small arteries and arterioles, surface structures representing aneurisms and edema were seen. Bronchial arteries were well developed and extremely dilated, and they formed numerous anastomoses with pulmonary arteries at all levels, from the pulmonary trunk to peripheral vessels. Capillaries in the lungs were dilated with little structural change. Small pulmonary veins and venules had irregular annular constrictions that were caused by hyperplastic smooth muscle cells of venous sphincters. CONCLUSIONS AND CLINICAL RELEVANCE: Scanning electron microscopy of microvascular casts delineated links between the bronchial and pulmonary circulations in dogs with dirofilariosis. Results of scanning electron microscopy provided a structural explanation for the development of pulmonary circulatory disturbances and pulmonary hypertension in dogs affected by dirofilariosis.

The incrimination of Aedes (stegomyia) aegypti as the vector of Dirofilaria repens in Nigeria.

Six local species of culicides were identified as the common mosquitoes in Zaria, out of 15 species captured using various adult and larval collection methods. These common culicides are Culex pipiens fatigans, Anopheles gambiae grp., Mansonia africana, Culex pipiens pipiens, Aedes (stegomyia) aegypti and Aedes vittatus. They were each fed directly on a local dog naturally infected with Dirofilaria repens to evaluate their refractoriness/susceptibility to dirofilarial infection. In a number of donor-feeding trials, 39. 4% Culex pipiens fatigans; 58.9% An gambiae grp.; 60.5% Mansonia africana; 1.8% of Culex pipiens pipiens; 23.4% Ae aegypti and 3.3% of Ae vittatus successfully fed on the microfilaraemic host. Only Aedes aegypti was susceptible to the infection as all 40 (100%) Ae aegypti reaching 10-14 day post-blood meal had infective (L(3)) larvae of D. repens. The remaining five species were refractory. The microfilariae in the five non-susceptible mosquitoes were always found trapped in the blood meal in the insects midgut (stomach). These trapped microfilaria were dead by the 2nd day in the insect's midgut. However, in the susceptible Ae aegypti, the microfilariae were set free from the blood meal in the midgut and within 24h migrated to the malpighian tubules (MT) of the mosquitoes. All Ae aegypti dissected 5-7 day post-infective blood meal showed the typical quiescent sausage stage (L(2)) larvae in the malpighian tubules. At day-10 post-blood meal, relatively active infective (L(3)) larvae of D. repens were found in the MT; and by day 12-14, highly motile infective larvae had reached the insect's head and proboscis, with infective larvae occasionally oozing out during dissection through the tip of the proboscis. The rate of development of D. repens to infective larvae was faster in mosquitoes infected in July when the environmental temperature was 24.5 degrees C than those infected in November when the temperature was 22.5 degrees C. The latter were delayed for 4 days. The breeding sources of Ae aegypti, the local vector implicated were also identified. As no particular vector of this zoonotic filaria has been identified previously in Nigeria, these findings could make any control programme more focussed and easier.

Microfilaremia from a Dirofilaria-like parasite in Greece. Case report.

In Europe, zoonotic filarial infections in humans are caused by two species, Dirofilaria immitis and Dirofilaria repens. These parasites are associated mainly with embolic infarcts of the pulmonary artery and subcutaneous nodules, respectively. An unusual dirofilarial infection in a Greek patient who showed marked eosinophilia and microfilaremia is presented. Although the identification of Dirofilaria species is not conclusive, this report is the first on a case of microfilaremia from a Dirofilaria infection in an immunocompetent patient.

The species of the genus Dirofilaria, Railliet & Henry, 1911.

Some authors divide the genus Dirofilaria into two subgenera. The subgenus Dirofilaria consists of 5 apparently valid species (D. ailure, D. freitasi, D. immitis, D. lutrae, D. spectans) and 7 species of questionable validity (D. fausti, D. indica, D. louisianensis, D. magalhaesi, D. nasuae, D. pongoi, D. spirocauda). The subgenus Nochtiella consists of 22 apparently valid species (D. acutiuscula, D. bonnei, D. cancrivori, D. corynodes, D. genettae, D. granulosa, D. incrassata, D. linstowi, D. macacae, D. macrodemos, D. magnilarvatum, D. minor, D. pagumae, D. panamensis, D. repens, D. sachsi, D. striata, D. subdermata, D. sudanensis, D. tawila, D. tenuis, D. ursi) and 8 species of questionable validity (D. aethiops, D. andersoni, D. conjunctivae, D. desportesi, D. hystrix, D. schoutedeni, D. spinosa, D. subcutanea). Actually, 10 species of the genus Dirofilaria (D. asymmetrica, D. digitala, D. kuelzii, D. ochmanni, D. pauliani, D. roemeri, D. scapiceps, D. timidi, D. uniformis, D. websteri) are attributed to other genus.

Importance in France of the infestation by Dirofilaria (Nochtiella) repens in dogs.

The presence of Dirofilaria repens has been mentioned in Europe, in Africa and in Asia, in different carnivores (dogs, foxes, cats, lions). In Europe the nematode has been reported in dogs, cats and foxes and the countries concerned by native cases are Italy, Spain, Greece, Yugoslavia and France. In France, until now, D. repens has been described, among animals, only in dogs. The first undoubted report dates back to 1953. Later, the prevalence was studied through widespread surveys (1986-1988-1989), focal surveys within some canine populations (military dogs) and some sporadic and fortuitous descriptions. The prevalence has been mainly assessed by pointing up the microfilariae in the blood and by identifying it after histochemical staining (for demonstration of the somatic distribution of acid phosphatase activity). The infestation rate was higher than 20% in some military dog populations. The cases occurred in nineteen French departments (Alpes-de-Haute-Provence, Aude, Bouches-du-Rhône, Corrèze, Corse, Dordogne, Gard, Gers, Gironde, Haute-Garonne, Loir-et-Cher, Nièvre, Pyrénées-Orientales, Rhône, Tarnet-Garonne, Var, Vaucluse, Vienne and Region Parisienne). The pathogenicity which is normally denied has to be reconsidered. The pathology of adult worms has not been clearly proved in dogs but the embolized microfilariae can bring about skin troubles. The potential pathogenicity, the necessity of the differentiation with D. immitis and above all, the zoonotic importance of D. repens must lead to search for it more often and to consider it with great interest.

Research of canine filariasis in Trapani province (western Sicily). Morphology on SEM of male Dirofilaria repens.

The prevalence of canine filariasis was investigated in 4 municipalities of Trapani province (Campobello di Mazara, Castelvetrano, Marsala and Mazara del Vallo), an area where 8 human cases of dirofilariasis due to Dirofilaria (Nochtiella) repens have occurred during the last decade. Blood samples were collected late in the afternoon, during August and September 1995, and examined by Knott technique for the presence of microfilariae. Sixtythree (29.3%) out of 215 domestic dogs (98 males, 117 females; 40 sub-adults, 175 adults) proved to be positive for microfilariae: 55 (25.6%) for D. repens, 13 (6.0%) for Dipetalonema reconditum, 1 (0.5%) for D. immitis; 6 (2.8%) mixed infections (5 D. repens + D. reconditum and 1 D. repens + D. immitis) were also found. The surface topography via SEM of an adult male specimen of D. repens found in a dog during necroscopy is also described. The relatively large number of human cases of dirofilariasis appears to be related to the high prevalence of D. repens observed in dogs of Trapani province. This matter should be investigated more extensively in this area.

Development of Dirofilaria and Setaria nematodes in Aedes albopictus.

The development of Dirofilaria repens, D immitis and Setaria labiatopapillosa up to L3 stage was documented in a laboratory colony of Aedes albopictus originating from specimens collected in Civitavecchia (Central Italy). The susceptibility of Ae albopictus and its plastic trophic habits, strongly suggest that this mosquito may contribute to the spreading of these nematodes in the country. It is particularly emphasized the danger for human health of an increased probability of transmission of Dirofilaria in urban areas.

[Human dirofilariasis: discovery of a gravid female of Dirofilaria repens in a subcutaneous nodule]. / Dirofilariasi umana: ritrovamento di femmina gravida di Dirofilaria repens in nodulo sottocutaneo.

A case of human subcutaneous dirofilariasis occurred in a 53 years old woman from Scafati (Salerno province). It was localized in the left submammary region. The patient was operated 16 years ago for a papillary carcinoma of the thyroid. For this reason a metastasis was clinically suspected. The histological examination revealed the presence of a granulomatous nodule formed around a Dirofilaria repens gravid female in the subcutaneous tissue. The presence of microfilariae in the uterus of the nematode would suggest that also a mature male was present at the same time in the patient, although it was not possible to localise it. Haematic eosinophilia was observed.

[Human pulmonary dirofilariasis: parasitological aspects of the 2d case reported in Italy]. / Dirofilariasi polmonare umana: aspetti parassitologici del secondo caso segnalato in Italia.

The parasitological aspects of a case of pulmonary human dirofilariasis, recently reported by Fabbretti and collaborators (1990) in a 58 year-old man from Ferrara province, are described. This is the second case of pulmonary human dirofilariasis recorded in Italy. The nematode was rolled up inside a small pulmonary artery and was associated with a nodular infarcted lesion, discovered during an X-ray check as a "coin lesion". A pulmonary lobectomy was performed on the patient with a presumptive diagnosis of a malignant neoplastic nodule. The exact diagnosis was only made with the histological examination. In spite of the bad preservation of the nematode, it was possible to diagnose it as an immature female of Dirofilaria probably belonging to the species repens.

Ivermectin against larval stages of Dirofilaria repens in dogs.

The prophylactic efficacy of ivermectin against Dirofilaria repens infections in dogs was investigated. A first trial was carried out on 15 dogs exposed to four inoculations of L3 larvae at 15-day intervals and treated, in groups of five, with 0, 6 or 12 micrograms/kg body weight of ivermectin given per os 30 and 60 days after the first inoculation. Necropsy, performed about 9 months later, revealed that worm burdens were reduced by 86.6 and 92.8% for the 6 and 12 micrograms/kg dose levels, respectively. In a second trial with an otherwise identical protocol, a dose rate of 24 micrograms/kg of ivermectin was tested in 12 dogs. Only one of the six treated dogs was found worm free at necropsy. The worm burden was reduced by 87.9% in treated animals as opposed to controls. A lengthening of the prepatent periods, which might be considered dose related, was apparent in all treated groups. Ivermectin was not completely effective in preventing establishment of experimental infections with D. repens in dogs.

A lambda gt11 cDNA recombinant that encodes Dirofilaria immitis paramyosin.

The cDNA synthesized from mRNA of Dirofilaria immitis female adult worms was cloned into the expression vector lambda gt11. Screening the library with a hyperimmune rabbit antiserum raised against adult worm homogenates yielded several antigen positive clones. One of these clones, lambda cDi2, was recognized by rabbit antisera raised against either D. immitis L-3, adult, Brugia malayi L-3 or Onchocerca volvulus adult worm antigen, as well as by antisera from humans naturally infected with O. volvulus or Wuchereria bancrofti. Affinity-purified anti-lambda cDi2 antibodies reacted with a 97-kDa protein on Western transfers of adult D. immitis antigen extracts that were reduced with beta-mercaptoethanol. The whole rabbit anti-D. immitis adult antiserum depleted of anti-lambda cDi2 antibodies exhibited decreased reactivity to this 97-kDa band. A monoclonal antibody (IA6) that specifically binds Schistosoma mansoni paramyosin also recognised a 97-kDa protein in D. immitis extracts upon Western transfer. The deduced amino acid sequence of partial DNA sequence from lambda cDi2 showed some similarity to nematode myosin, and gave a stretch of 82 amino acids that is 91.5% identical to Caenorhabditis elegans paramyosin: thus, lambda cDi2 encodes D. immitis paramyosin.

The effect of repeated blood meals on the larval development of Dirofilaria corynodes in the fat body of Aedes aegypti.

The objective of the study was to determine whether blood meals taken by a vector subsequent to the infective one have any influence on the course of development of a filarial parasite in its tissue. The filaria Dirofilaria corynodes (von Linstow, 1899) was selected for study and the black-eye strain of Aedes aegypti served as the experimental vector. The microfilaria of D. corynodes develops to the infective stage in the fat bodies of the vector. Following an infective blood meal, mosquitoes were maintained on 10% sugar water alone (group A) or received supplementary blood meals i.e., an uninfected blood meal prior to the first larval molt followed by another after it (group B), an early blood meal (group C) or a late blood meal (group D). It was observed that additional blood meals after the infective one enhance the rate of larval development regardless of the timing of the feedings. An early blood meal, even if it is the only one, has a long-term significant effect on development. Repeated blood meals do not have an additive effect but tend to result in greater uniformity in larval size. A late blood meal also has a positive effect on development although the larval filariae do not grow or mature as rapidly as in the groups already mentioned. Larvae from mosquitoes fed on sugar water alone tended to develop at a slower rate and with less uniformity. It is concluded that infected mosquitoes taking one or more additional blood meals will yield a larger number of infective larvae in a shorter period of time.

Efficacy of ivermectin against Dirofilaria immitis larvae in dogs 30 and 45 days after induced infection.

Forty-two Beagles, 14 to 15 weeks of age, were injected subcutaneously with 50 infective larvae of Dirofilaria immitis and were allotted by weight, within sex, to 6 treatment groups. Group 1 served as nonmedicated vehicle-treated controls; groups 2 through 5 were given an oral tablet form of ivermectin at dosages of 0.3 micrograms/kg, 1.0 micrograms/kg, 2.0 micrograms/kg, and 3.3 micrograms/kg at 30 days after inoculation; group 6 was given the 2.0 micrograms/kg dosage at 45 days after inoculation. Dogs were euthanatized and necropsied 154 days after treatment (day 139 for dogs in group 6) and examined for heartworms. On the numerical bases of helminths recovered in the groups, the efficacies for preventing heartworm maturation were 0% (group 2), 53.2% (group 3), 97.2% (group 4), 98.1% (group 5), and 63.8% (group 6). Drug-related adverse reactions were not detected.