Dirofilaria repens Railliet and Henry, 1911
ETYMOLOGY: Diro = dread + filaria = thread along with repens = creeping
SYNONYMS:Filaria acutiuscula Molin, 1858; Dirofilaria conjunctivae (Addario, 1885) Desportes, 1940.
HISTORY: The parasite first was described from the dog by Railliet and Henry (1911a&b). Desportes (1940) first recognized that the worm Filaria conjunctivae Addario, 1885, may have been the same species as that found in the dogs. Skrjabin (1917) described a human case under the name of Loa extraocularis, and Skrjabin et al. (1930) attributed a second human case to Dirofilaria repens. In 1948, Skrjabin and Schikhobalova recognize Loa extraocularis as a sysnonym of Dirofilaria repens. Cacrini et al. (1990) felt that the laws of priority were such that the worm should be called Dirofilaria conjunctivae (Addario, 1885); but this designation has not been currently adopted..
GEOGRAPHIC LOCATION: Chauve (1990) presents the distribution of Dirofilaria repens in dogs as including Nigeria and Uganda in Africa, along with Turkey, Italy, and France in Europe. Human cases have been reported from Italy, Greece, France, and other Mediterranean countries (Pampiglione et al., 1995; Pampiglione et al., 1996), parts of Russia (Avdyukhina et al, 1997), Africa (O’Grady et al,. 1962); Israel (Zweig et al,m 1981), Sri Lanka (Dissanaike et al., 1972), and Okinawa (MacLean et al., 1979).. Cats have been found to be infected in Malaysia (Chang et al, 1992; Mak et al, 1985; Rohde, 1962) and on the Pate island off the coast of Kenya (Heisch et al 1959). Cats and dogs have also been found infected in India (Patnaik, 1989) and Indonesia (Palmieri et al., 1985). Interestingly, the cats in the Mediterranean do not seem to support infections with this parasite in this locality, although Pampiglione et al (1995) cite a personal reference from Dr Genchi that a cat has been observed infected in Italy. .
LOCATION IN HOST: The adult worms are rather large, males are 5 to 7 cm and females are 10 to 17 cm long, and are found in the subcutaneous connective tissues of their hosts.
LIFE CYCLE: The adults live in the subcutaneous tissues. Microfilariae (about 300 μm long) are found in the blood and seem to be slightly periodic being more common in the peripheral blood at night (Webber and Hawking, 1955). Mosquitoes of several different genera serve as the intermediate hosts (Bernard and Bauche, 1913; Fülleborn, 1908), and it takes about 9 to 21 days for the larvae to become infective depending on the temperatures at which the mosquitoes are held. Gunewardene (1956) recovered infective larvae from mosquitoes (Aedesalbopictus) by 12 days after infection. Mosquitoes incriminated as potential hosts (acc. To Manotovani and Restani, 1965) include Aedes alpopictus, Aedes aegypti, Aedes albifasciatus, Psorophora cyanescens, Anopheles maculipennis, Anopheles petragnanii, Anopheles claviger, Anorpheles atroparvus, Anopheles hyrcanus, Anopheles stephensi, Anopheles barbirostris, Mansonia uniformis, Mansonia annulifera, Mansonia titillans, and Armigere sobturbans. Bain (1978) studied the development of the larvae in Aedes detritus and Aedes caspius. She described the morphology of the larval stages developing within these mosquitoes. Webber and Hawking (1955) inoculated dogs with infective larvae and found the prepatent period to be about 6 months, 25 to 34 weeks. Microfilariae would circulate in the blood of infected dogs for 2 to 3 years.
CLINICAL PRESENTATION AND PATHOGENESIS: There are a few reports regarding pathology or clinical presentation in cats infected with this parasite. Tarello (2011) reviews what he saw in a case series of 31 cats:
“Among 31 cats with subcutaneous dirofilariasis [4, 5, 12–14], symptoms observed more often were pruritus (100%), alopecia (77.4%), erythema (74.2%), papulae (51.6%), and crusting (29%).
Symptoms and signs other than dermatological were as follows: anorexia (35.5%), lymphadenomegaly (32.3%), pale mucous membranes (29%), lethargy (16%), conjunctivitis (16%), pain (16%), and fever (10%) [4, 5, 12–14]. Concurrent infection with haemobartonellosis (Mycoplasma haemofelis infection), or Feline Infectious Anemia, which is transmitted by fleas or ticks, was recorded in 25 (80%) out of 31 cats examined and its therapy with doxycycline (10mg/kg, for 20 days) greatly contributed to the clinical resolution [4, 5, 12–14]. Doxycycline is important in the therapy of dirofilariasis because it also eradicates the Wolbachia spp. bacteria symbiotic of adult worms, causing their sterilization and death .” (The references in the preceding quote can be found in the original paper.)
TREATMENT: There have been no descriptions of treatment in the cat.
EPIZOOTIOLOGY: The most intriguing aspect of the epizootiology of infections with this parasite is the fact that it seems much more common for cats to be infected in southeast Asia than in southern Europe. This could be due to either different strains of the parasite or host being present in these two parts of the world, or it may be that the mosquitoes in southeast Asian are more likely to feed on both dogs and cats and thus, transmit the parasite between these two hosts.
HAZARDS TO OTHER ANIMALS: The cat really poses no threat to other animals. In southeast Asia where cats have circulating microfilariae, it is possible that cats could serve as reservoirs for canine or human infections.
HAZARD TO HUMANS: There have been numerous infections with Dirofilaria repens. An excellent review of human infections by Pampiglione et al. (1995). There have been nearly 400 cases in people, with most cases, slightly less than half, occurring in Italy. Most of the cases have occurred as worms appearing in subcutaneous nodules on the head, thoracic wall, or upper limbs. Occasionally, worms may cause lesions in deeper tissues, and on rare occasions lesions in the lungs have been mistaken for malignancies. Of course, human infections are acquired by the bite of a mosquito in a fashion similar to that by which dogs and cats become infected.
CONTROL/PREVENTION: Marconcini et al (1993) have shown that monthly ivermectin at the heartworm preventative dose of 6 μg/kg is capable of preventing dogs from becoming infected with Dirofilaria repens. Thus, it is to be expected that the use of monthly ivermectin in the cat would also prevent infection of cats with Dirofilaria repens.
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