Absence of shock-like reactions to ivermectin in dogs infected with Dirofilaria immitis

Six dogs infected with Dirofilaria immitis and known to develop shock-like reactions after administration of diethylcarbamazine (DEC) were given ivermectin 50 micrograms/kg orally. None of the dogs showed any adverse reaction and subsequently all reacted to DEC 20 mg/kg orally.     

Combined ivermectin and doxycycline treatment has microfilaricidal and adulticidal activity against Dirofilaria immitis in experimentally infected dogs

There is still a pressing need for effective adulticide treatment for human and animal filarial infections. Like many filarial nematodes, Dirofilaria immitis, the causative agent of canine heartworm disease, harbours the bacterial endosymbiont Wolbachia, which has been shown to be essential for worm development, fecundity and survival. Here the authors report the effect of different treatment regimens in dogs experimentally infected with adult D. immitis on microfilariemia, antigenemia, worm recovery and Wolbachia content. Treatment with ivermectin (IVM; 6 microg/kg per os weekly) combined with doxycycline (DOXY; 10 mg/kg/day orally from Weeks 0-6, 10-12, 16-18, 22-26 and 28-34) resulted in a significantly faster decrease of circulating microfilariae and higher adulticidal activity compared with either IVM or DOXY alone. Quantitative PCR analysis of ftsZ (Wolbachia DNA) and 18S rDNA (nematode DNA) absolute copy numbers showed significant decreases in Wolbachia content compared with controls in worms recovered from DOXY-treated dogs that were not, however, associated with worm death. Worms from IVM/DOXY-treated dogs, on the other hand, had Wolbachia/nematode DNA ratios similar to those of control worms, suggesting a loss of both Wolbachia and nematode DNA as indicated by absolute copy number values. Histology and transmission electron microscopy of worms recovered from the IVM/DOXY combination group showed complete loss of uterine content in females and immunohistochemistry for Wolbachia was negative. Results indicate that the combination of these two drugs causes adult worm death. This could have important implications for control of human and animal filarial infections.     

Experimental infection of cats with Dirofilaria immitis.

Natural and experimental infections of cats with Dirofilaria immitis have been reported. Experimental infections of D. immitis in cats with the subsequent detection of microfilaremia and immediate skin hypersensitivity to antigen to D. immitis were produced. Cutaneous nodules and chylothorax were also detected in some infected cats. Adult worm recoveries were low and dead worms were found in some cats indicating the unsuitability of the cat as a host for D. immitis. However, one successful mosquito passager of D. immitis from a cat to a dog was accomplished.     

Phosphatidylcholine synthesis in adult Dirofilaria immitis females

Crude homogenates of adult Dirofilaria immitis females were able to incorporate choline into phosphatidylcholine (PC) and also were able to methylate phosphatidyl (N,N-dimethyl)-ethanolamine, using S-adenosylmethionine as the methyl donor, to form PC. The finding of choline phosphotransferase (EC 2·7·8·2) and phosphatidyl (N,N-dimethyl) ethanolamine methyltransferase activity in the paniculate (mainly microsomal) fraction of the homogenates provided further evidence that adult D. immitis females can synthesize PC by way of choline and cytidine 5'-diphosphocholine (Kennedy pathway) and also by way of S-adenosylmethionine-mediated sequential methylation of phosphatidylethanolamine (Bremer-Greenberg pathway).     

Phosphatidylethanolamine synthesis in adult Dirofilaria immitis females

Srivastava Arvind K., Jaffe Julian J. and Lambert Roger A. 1985. Phosphatidylethanolamine synthesis in adult Dirofilaria immitis females. International Journal for Parasitology15: 429–433. Adult Dirofiliaria immitis females were found able to synthesize phosphatidylethanolamine (PE) by way of the following three pathways: (1) phosphorylethanolamine, cytidine diphosphoethanolamine and 1,2-diacylglycerol; (2) decarboxylation of phosphatidylserine (PS); and (3) direct exchange of ethanolamine for choline or serine in preformed phosphatidylcholine or PS. The latter two pathways were confined to the paniculate fraction of worm homogenates. Under stated assay conditions, the respective rates of PE formation by way of these pathways in the order given were around 250, 8500 and 2–3 pmol min^?1 mg^?1 protein.     

Treatment and prevention of natural heartworm (Dirofilaria immitis) infections in red pandas (Ailurus fulgens) with selamectin and ivermectin

Ten of the 48 red pandas in the Chengdu Research Base of Giant Panda Breeding, Sichuan province, China, died in 2006 after prolonged periods of depression, weight loss, and mucocutaneous membrane xanthochromia. During postmortem examination, live heartworms were found in the right cardiac ventricles and pulmonary arteries of all 10 animals. Selamectin and ivermectin were used for clinical prophylaxis in the remaining red pandas between December 2006 and November 2010. We observed a gradual decrease in morbidity and mortality during this period. As a consequence of our prophylaxis program, dirofilariosis did not occur in the remaining red pandas at Chengdu Research Base during 2010.     

Isoenzyme variation in Aedes aegypti correlated with Dirofilaria immitis infectability

From the Vero Beach strain of the mosquito Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae), substrains were selected for susceptibility (SS) and refractoriness (RR) to the dog heartworm Dirofilaria immitis (Leidy) (Filarioidea: Onchocercidae). These two lines and their reciprocal F1 hybrids were analysed for genetic variation at 14 enzyme loci, using polyacrylamide gel electrophoresis. Six of the enzyme loci showed variation (sample size 48 alleles/locus/line). Three of these were monomorphic in the refractory line but polymorphic in the susceptible, i.e. aconitase hydratase (Acoh), isocitrate dehydrogenase-1 (Idh-1) and phosphoglucomutase (Pgm). The other three loci, glucose-6-phosphate isomerase (Gpi), hexokinase-1 (Hk-1) and isocitrate dehydrogenase-2 (Idh-2), were polymorphic in both SS and RR lines and their hybrids. At two loci (Hk-1, Pgm) three alleles were detected, whereas the other polymorphic loci had only two alleles. For Hk-1, the most frequent allele was Hk-1(80) (0.563) in refractory and Hk-1(100) in the susceptible (0.521) and F1 hybrids. For Pgm the most frequent alleles were Pgm125 in the susceptible line (0.646) and Pgm100 in the F1 hybrids (0.563 and 0.604) and refractory line (1.000). The mean observed heterozygosity (Ho), the mean Hardy-Weinberg expected heterozygosity (He) and the mean number of alleles per locus in the refractory line were lower, but not significantly so, than in the susceptible line and their reciprocal F1 hybrids; the proportion of polymorphic loci was significantly lower in the refractory than in the susceptible line and their F1 hybrids. Within both lines all polymorphisms were in Hardy-Weinberg equilibrium, whereas significant departures from predicted frequencies were observed in SS x RR hybrids at four polymorphic loci (Acoh, Gpi, Hk-1, Pgm) and at three polymorphic loci (Acoh, Hk-1, Pgm) in RR x SS hybrids. The average Nei's and modified Rogers' genetic distances between the lines were 0.024 and 0.139, respectively. These electrophoretic data show that the refractory line (putatively lacking fi allele) can be distinguished from the susceptible line (fi/fi) and their hybrids (heterozygous fi) by isozyme marker frequencies, but it remains to be seen whether this difference is causal or chance linkage. In any case, this model system of Ae. aegypti/D. immitis provides opportunities to better understand and manipulate the molecular biology of filariasis transmission.     

Experimental infection of Dirofilaria immitis in raccoon dogs

Canine heartworm (Dirofilaria immitis) is a nematode that naturally parasitizes in the pulmonary arteries and the right ventricle of domestic dogs (Canis familiaris) as final hosts. Japanese raccoon dogs (Nyctereutes procyonoides viverrinus) also are known to be susceptible to infection by the parasite. However, prevalence of this infection among free-ranging raccoon dogs is low and so is the worm burden. To examine the susceptibility of the raccoon dog to D. immitis infection, 3 raccoon dogs and 2 beagles were inoculated 4 times with 25 third-stage larvae (L3s) of D. immitis at 3-wk intervals. Worms were recovered from 2 raccoon dogs and both domestic dogs. The average percentage of recovery (2.3%) of the raccoon dogs was almost 10 times lower (24.5%) than that of the domestic dogs, but there was no significant difference in the body length of worms recovered from 2 types of hosts. To examine microfilaremia, 2 raccoon dogs were infected with 100 L3s. Microfilaremia was observed for 180 days postinoculation (PI) but disappeared at about 300 days PI. The raccoon dog was mildly susceptible to infection with D. immitis, but surviving worms developed and matured normally.     

Dirofilaria immitis in coyotes and foxes in Missouri

Wild canid carcasses were obtained during the 1986-1987 and 1987-1988 trapping seasons in Missouri. Hearts and lungs from 293 coyotes (Canis latrans), 85 red foxes (Vulpes vulpes) and 70 gray foxes (Urocyon cinereoargenteus) were examined for Dirofilaria immitis. Age of hosts was determined by radiographic and histologic techniques. Nineteen coyotes (7%) had from 1 to 100 D. immitis and five red foxes (6%) had from 1 to 7 D. immitis, whereas gray foxes had none. This study indicates that heartworm prevalence differs by wild canid species within the same area and during the same time period.     

Spontaneous flight activity of Aedes trivittatus infected with Dirofilaria immitis

Spontaneous flight activity of Dirofilaria immitis-infected Aedes trivittatus was evaluated by using an acoustic activity system. The activity of mosquitoes infected with low numbers of filarial larvae (1-4) was similar to that of uninfected mosquitoes. However, mosquitoes infected with more than 4 larvae became more active than uninfected mosquitoes 8 days after infection. Peak flight activity (circadian) occurred at the same time in both infected and uninfected mosquitoes, but infected mosquitoes were much more active during normal periods of quiescence. Flight activity of mosquitoes infected with more than 4 larvae was suppressed on days 10 and 14 postinfection, corresponding to times of greatest disruption of the Malpighian tubules by the developing larvae.     

Thermotaxis in third and fourth-stage Dirofilaria immitis larvae

Third-stage and fourth-stage Dirofilaria immitis larvae exhibited positive thermotaxis when placed in a thermal gradient. Negative thermotaxis was not observed. Positive thermotaxis may be important for the successful transmission and for directing third and fourth-stage larval migration toward predilection sites in the host.     

Inference of population structure and patterns of gene flow in canine heartworm (Dirofilaria immitis)

Understanding the genetic variation within a parasitic species is crucial to implementing successful control programs and preventing the dispersal of drug resistance alleles. We examined the population genetics and structure of canine heartworm (Dirofilaria immitis) by developing a panel of 11 polymorphic microsatellite loci for this abundant parasite. In total, 192 individual nematodes were opportunistically sampled from 9 geographic regions in the United States and Mexico and genotyped. Population genetic analyses indicate the presence of 4 genetic clusters. The canine heartworm samples used in this study were characterized by low heterozygosity, with eastern and central North America experiencing high levels of reciprocal gene flow. Geographic barriers impede the movement of vectors and infected hosts west of the Rocky Mountains and south of the Central Mexican Plateau. This, combined with corridors of contiguous habitat, could influence the spread of drug resistance alleles.