Filarial nematode Dirofilaria immitis. Adult males measure 12 to 18 cm, and females can measure up to 30 cm, with a diameter of 1 mm, and are whitish in colour. Females lay sanguiculous microfilariae, measuring around 300 µm long and 6 µm in diameter.
Female Culicidae: Culex, Aedes, Mansoni, Anopheles. Dirofilaria can be transmitted by all genera and all species, but the capacity of one species or another to act as vector varies from one region to another.
Learn more about the vectors: Mosquitoes
Other carnivores can also be infested: cats, mustelids (one of which is the ferret), sea-lions, seals etc. Cats are infested in areas where the disease is highly-endemic but they are less receptive than dogs.
Threadworm is most frequently found in inter-tropical areas (Africa, Asia, Australia, Central and South America, Pacific Islands) where the prevalence of infestation may range from 20% to more than 60% in dogs. But it can also be found in places such as Canada and Japan and in most of the United States (although to a greater extent in the South: Florida, Louisiana).
It is present in southern Europe and particularly around the Mediterranean: Spain, Italy, and Greece. It has been described in the southernmost part of France (Provence) although only sporadically (prevalence of less than 0.7%). It is endemic in Corsica and Sardinia. It is endemic in certain Eastern European countries (Romania).
General signs: development of heart failure with the progressive appearance of cardiorespiratory symptoms sometimes associated with other symptoms.
Dogs harbouring few worms do generally not present any clinical signs.
Cutaneous signs: pruritus, loss of hair, necrosis of the extremities (ears, tail).
Nervous signs: most often paresis, lack of motor coordination, sometimes convulsions, stages of aggressiveness, temporary loss of consciousness.
Haemorrhagic signs: melena, epistaxis, haemoptysis.
Sight-related signs: periodic ophthalmia
Kidney impairment: chronic renal failure
Clinical signs
(right-side heart failure confirmed by auscultation) + epidemiology
Laboratory
Blood tests reveal regenerative anaemia. Hypereosinophilia is possible, but not systematic.
Serology: tracing circulating filariae antigens (requires ELISA kits).
Confirmation of infestation comes from the appearance of blood microfilariae
Complementary tests
An echocardiogram, rather than an X-ray, helps diagnose cardiopulmonary threadworm by revealing the existence of parasites.
It is not advisable to treat asymptomatic infested dogs.
- Use of melarsomine (2 intramuscular injections 24 hours apart).
- Anti-thrombosis treatment (anti-coagulant).
Use of avermectins/milbemycins, oral administration
Cats are less receptive than dogs but still always have the potential to be hosts.
The infection is more difficult to detect, the length and number of worms in cats are smaller than in dogs. The clinical signs are more pulmonary (dyspnoea, coughing, oedema) and there are rarely cardiac signs. The diagnosis and the treatment is the same as for dogs.
