Dirofilariosis
Pathogen
Dirofilaria repens -nematod (roundworm)
Vector
Mosquitoes (e.g. Aedes, Culex, Anopheles)
Geographical distribution
Throughout Europe, reaching as far north as Estonia and Latvia. In Finland, one indigenous human infection has been reported. No indigenous infections in dogs have been reported in the Nordic countries.
Transmission
Dirofilaria repens is transmitted through mosquito bites. Its lifecycle is similar to that of D. immitis. Mosquitoes ingest microfilariae (the immature stages of the worm) from the bloodstream of an infected dog or cat during a blood meal. These microfilariae migrate to the mosquito’s body cavity, where they undergo development and transformations. Eventually, they move to the mosquito’s mouthparts and develop into an infectious larval stage. During a subsequent blood meal, the mosquito transmits the larvae into a new host—usually a dog or cat (or more rarely, a human). The infectious larvae enter the host’s skin through the mosquito bite and migrate through the subcutaneous and muscle tissues for several months. D. repens settles in the subcutaneous tissue, where it begins producing microfilariae that enter the bloodstream approximately six months after infection.
Symptoms
Dirofilaria repens does not cause systemic disease in dogs or cats but often results in relatively harmless skin changes. In severe infections, the parasite can also be found during surgical procedures in locations such as muscle sheaths, fat surrounding the kidneys, the abdominal cavity, or even the conjunctiva of the eye. In heavy infestations, the skin may exhibit pustules, ulcers, and itching.
Prevention
Preventive treatment with microfilaricidal macrocyclic lactones (moxidectin, selamectin, ivermectin, milbemycin) is recommended once a month during mosquito season (in Southern Europe, from at least May to November, or year-round in high-risk areas). When traveling from Finland (a non-endemic area) to Eastern or Southern Europe (endemic areas) for a trip lasting less than a month, the animal should be treated at least once within 30 days of the start of exposure. If staying in the area for a longer period (over 1 month), treatment should be repeated every 30 days and again within 30 days after leaving the risk area upon returning home. In some European countries, there is an injectable formulation (moxidectin) available that provides protection for up to a year. This can be a useful alternative to monthly oral treatments for longer stays in high-risk areas. Mosquito-repellent products can also be beneficial, such as the Scalibor collar (deltamethrin) or Vectra 3D spot-on solution (permethrin + dinotefuran). However, these products must NOT be used on cats!
Other Considerations
Dirofilaria repens is a zoonosis, meaning it can also infect humans. However, it requires a mosquito as a vector and does not transmit directly from cats or dogs.
Lähteet:
Deksne G, Jokelainen P, Oborina V, Lassen B, Akota I, Kutanovaite O, Zaleckas L, Cïrule D, Tupïts V, Talijunas A, Krümina A. The Zoonotic Parasite Dirofilaria repens Emerged in the Baltic Countries Estonia, Latvia, and Lithuania in 2008-2012 and Became Established and Endemic in a Decade. Vector-borne and Zoonotic Diseases 2021, 21:1-5
ESCCAP 2019 (European Scientific Counsel Companion Animal Parasites). Guideline 05 Control of Vector-Borne Diseases in Dogs and Cats, Third Edition.
Pietikäinen R, Nordling S, Jokiranta S, Saari S, Heikkinen P, Gardiner P, Kerttula A- M, Kantanen T, Nikanorova A, Laaksonen S, Lavikainen A, Oksanen A. Dirofilaria repens transmission in southeastern Finland. Parasites & Vectors 2017, 10:561
Saari S, Näreaho A, Nikander S. Elinympäristönä koira, koiran loiset ja loissairaudet. 1. p. Fennovet Oy, Helsinki, Suomi 2016