Introduction

Classification

Taxonomy

• Superfamily: Filarioidea
• Familie: Onchocercidae
• Genus: Dirofilaria
• Species: repens

Active Forms

Resting Forms

Clinical Effects

Epidemiology

Habitat

• The adults situated in nodules are found in the subcutaneous tissue and the perimuscular connective fasciae in the whole body, with a higher proportion in the trunk and less in the legs and head. Very often the nodules are randomly found and it can be assumed that many of them remain undetected.
• The larval stages in the subcutaneous tissue of dogs can be found close to the location where they will be situated as adults.
• Microfilariae are shed by the adult females and circulate in the blood.

Lifecycle

• For the development of D. repens two hosts final and intermediate - are obligatory . Dogs, cats and wild canids act as final hosts where the sexual maturation takes place. In these hosts the progeny, so called microfilariae, are shed into the circulation blood and await the uptake by a suitable intermediate hosts. Here mosquitoes act as hosts and vector for transmission at the same time. The uptake of the microfilariae is essential for the further development of the nematode to L2 and the infective L3 which situates in the cephalic region of the mosquito.
• During the blood meal of the mosquito, the L3 leaves the mosquito actively and uses the mosquito's bite to enter the final host. There it molts to L4 and the development into immature young adults occurs in the nearby subcutaneous tissue. After a development period of 6-8 months in the host tissue, the adults shed microfilariae again. These are released into the blood stream, where other mosquitoes take them up during the blood meal. In the mosquito the development to the infective L3 takes about 2-3 weeks. During a second mosquito bite L3 reaches other dogs.

Transmission

• The transmission only can take place during a bite of a mosquito harboring the infective L3 (3rd stage larvae) in the cephalic region.

Pathological effects

• Presumably the most common effects of an infection are asymptomatic.
• The painless subcutaneous nodules, in which the adults are found, normally do not produce any clinical signs. Therefore many infections remain undetected, especially when these nodules are situated deeper underneath the skin surface of the dog.
• In the rarely occurring case of a clinical manifestation two syndromes are described. One, leading to a nodular multifocal dermatitis, which is almost localized in the facial region. The other syndrome involves several pruritic papulae, similar to sarcoptic mange.
• Dermal swellings and dermatological signs (such as generalized dermatitis, localized alopecia, scratching and rubbing) are described in some cases.
• In dogs with heavy infections histopathological changes in organs (liver, spleen, kidney, lung, heart, brain) were found. It was assumed that a combination of mechanical and immunopathological effects caused by macro- and microfilariae lead to this changes, although this has not been proven.
• A cutaneous hyperpigmentation in a dog was attributed to D. repens infection.

Other Host Effects

• In some cases the nodules a situated at aberrant locations (conjunctiva) and can cause troubles due to tissue displacement and inflammatory reaction at these sites.

Host interaction

• D. repens has been described in cats, genet cats, lions, foxes and humans.
• Acute liver failure of a cat was described in a case report.
• In humans the nematodes rarely reach full maturity and the ability to shed microfilariae into the blood stream.

Control

Control via chemotherapies

• Prophylaxis is suggested to avoid an infection of dogs when living in or traveling to an endemic area. Macrocyclic lactones are recommended in various formulations and combinations. In southern Europe, 6 months of continuous treatment (mid May to mid November) is suggested.
• Treatment of dogs harboring adults is recommended since these act as reservoirs and could be responsible for further spreading of the nematode.
• The microfilaricide effects of avermectins interrupt the lifecycle of the worm by removing microfilariae from the circulation blood.
• An off-label use of the treatment against D. immitis (melarsomine Melarsomine combined with doramectin) was suggested for both adulticidal and microfilaricidal effects. This could lead to massive adverse effects due to the use of organic arsenical chemotherapeutic agent melarsomine dihydrochloride. Although a clearance of D. repens infection was shown, the risks for treatment of the dog (especially in subclinical cases) and the prevention of further spreading should be evaluated for each case. The latter can also achieved with microfilaricidal treatment without severe side effects.
• Recently a more convenient formulation for D. repens treatment was described. The use of moxidectin Moxidectin combined with imidacloprid Imidacloprid as spot on delivered satisfying results. The microfilaricidal effect could be confirmed and an adulticidal effect was suggested, based on the fact that microfilariae were not shed again 6 months to one year after the treatment of infected dogs. Further investigations are needed to confirm and understand these effects.

Control via surgery

• Nodules in the skin of dogs are removed and subsequently diagnosed as D. repens infections.
• Surgical extraction of nodules is possible, but it is difficult to remove all nodules allocated in a patient. Therefore control for the presence of microfilariae is recommended and if larvae are found in the blood, microfilaricidal treatment to prevent further transmission is suggested.

Control via environment

• Mosquitoes as intermediate hosts and transmission vectors could be the major target for control of D. repens in the environment. Elimination of mosquitoes by using chemicals might help, but this is cumbersome and the effects on the ecosystem are unknown. Vector bites could be prevented by using nets and repellents on individual humans and pets. Repellents such as pyrethroids could be applied as collar, spot on etc. Furthermore the exposure of dogs to mosquitoes could be reduced if they are kept in locations free of mosquitoes.

Vaccination

• Not available.

Other countermeasures

• People traveling with dogs or importing them from endemic areas should be informed about the risk. If these pets are not treated, testing for microfilariae after the prepatent period is advised.

Diagnosis

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Fok E, Jacsó O, Szebeni Z et al (2010) Elimination of Dirofilaria (syn. Nochtiella) repens microfilariae in dogs with monthly treatments of moxidectin 2.5%/imidacloprid 10% (Advocate®, Bayer) spot-on. Parasitol Res 106 (5), 1141-1149 PubMed.
• Genchi M, Pengo G, Genchi C (2010) Efficacy of moxidectin microsphere sustained release formulation for the prevention of subcutaneous filarial (Dirofilaria repens) infection in dogs. Vet Parasitol 170 (1-2), 167-169 PubMed.
• Duscher G, Feiler A, Wille-Piazzai W et al (2009) [Detection of Dirofilaria in Austrian Dogs.] Berl Munch Tierarztl Wochenschr 122 (5-6), 199-203 PubMed.
• Duscher G, Peschke R, Wille-Piazzai W et al (2009) Parasites on paper-The use of FTA Elute® for the detection of Dirofilaria repens microfilariae in canine blood. Vet Parasitol 161 (3-4), 349-351 PubMed.
• Genchi C, Rinaldi L, Mortarino M et al (2009) Climate and Dirofilaria infection in Europe. Vet Parasitol 163 (4), 286-292 PubMed.
• Pantchev N, Norden N, Lorentzen L et al (2009) Current surveys on the prevalence and distribution of Dirofilaria spp. in dogs in Germany. Parasitol Res 105 (Suppl 1), S63-S74 PubMed.
• Miterpáková M, Antolová D, Hurníková Z et al (2008) Dirofilariosis in Slovakia - a new endemic area in Central Europe. Helminthologia 45 (1), 20-23 VetMedResource.
• Keller L, Hartmann K, Wess G (2007) Diagnostic approach to microfilaremia. Case report and review of cutanous dirofilariasis. Tierarztl Prax 35 (1), 31-34 VetMedResource.
• Kramer L H, Kartashev V V, Grandi G et al (2007) Human subcutaneous dirofilariasis, Russia. Emerg Inf Dis 13 (1), 150-152 PubMed.
• Hermosilla C, Pantchev N, Dyachenko V et al (2006) First autochthonous case of canine ocular Dirofilaria repens infection in Germany. Vet Rec 158 (4), 134-135 PubMed.
• Tilakaratne W M, Pitakotuwage T N (2003) Intra-oral Dirofilaria repens infection: Report of seven cases. J Oral Pathol Med 32 (8), 502-505 PubMed.
• Baneth G, Volansky Z, Anug Y et al (2002) Dirofilaria repens infection in a dog: diagnosis and treatment with melarsomine and doramectin. Vet Parasitol 105 (2), 173-178 PubMed.

Other sources of information

• Genchi C, Venco L, Genchi M (2007) Guideline for the laboratory diagnosis of canine and feline Dirofilaria infections. Genchi C, Rinaldi L, Cringoli G. Veterinary Parasitology and Parasitic diseases 8, Naples.
• Grandi G, Zivicnjak T, Beck R (2007) Pathogenesis of Dirofilaria spp. infections. Genchi C, Rinaldi L, Cringoli G. Veterinary Parasitology and Parasitic diseases 8, Naples.
• Manfredi M T, Cerbo Ad, Genchi M (2007) Biology of filarial worms parasitizing dogs and cats. Genchi C, Rinaldi L, Cringoli G. Veterinary Parasitology and Parasitic diseases 8, Naples.
• Pampiglione S, Rivasi F (2000) Human dirofilariasis due to Dirofilaria (Nochtiella) repens: an update of world literature from 1995 to 2000. Genchi C, Rinaldi L, Cringoli G. Veterinary Parasitology and Parasitic diseases 8, Naples.