Acanthocheilonema reconditum

Synopsis

CAPC Recommends:

• Microfilariae are present in the blood and can be mistaken for other parasites. Distinguish between Acanthocheilonema reconditum and Dirofilaria immitis microfilariae circulating in blood by modified Knott’s procedure.
• Protect susceptible dogs from infection by controlling the arthropod vectors, specifically fleas and lice.

Species

Canine

Acanthocheilonema reconditum

Acanthocheilonema reconditum microfiaria in canine blood

Overview of Life Cycle and Stages

• Microfilariae (237–288 um) are found in the blood and skin of most infected canines, most frequently in low numbers.
• During the blood meal microfilariae are ingested by fleas or lice where they undergo two molts to the infective stage (L3) in 6–15 days depending on environmental temperature.
• The transmission of the infective L3 stage likely occurs during either the blood meal or by ingestion of the infected arthropod vector. Currently the exact route of transmission is unclear.
• Very little information is known on the development within the host after transmission. After transmission, the larvae continue to develop into adults located most likely in the subcutaneous tissue primarily of the back, trunk and hind limbs.
• Gravid females release microfilariae which are believed to enter the circulation either by direct penetration or through the lymphatics.
• Microfilariae are first detected in the blood approximately 61–100 days post infection and must be distinguished from those of Dirofilaria immitis. (See Diagnosis)

Disease

• A. reconditum is considered to be non-pathogenic and there is no evidence to suggest that this infection causes disease.

Host Association and Transmission Between Hosts

• The cat flea (Ctenophalides felis) is the primary vector although other fleas (Ctenophalides canis, Pulex irritans, Pulex simulans, and Echidnophaga gallinae) as well as lice (Heterodoxus springer and Linognathus setosus) are all considered competent vectors.
• A. reconditum infected dogs that are not on routine prophylactic preventives for fleas/lice serve as reservoirs for infection between dogs in close proximity such as dogs within the same household, co-housing or in a kennel environment.

Prepatent Period and Environmental Factors

• The prepatent period, as determined by when microfilariae are first detected in the blood, ranges from 61–100 days and patency extending as long as 795 days.
• Ambient temperature affects the rate of development of ingested microfilariae in fleas to the L3 infective stage (6–15 days) based on experimentally acquisition fed fleas.

Site of Infection and Pathogenesis

• Adults are found in the subcutaneous tissues and muscle. Females release microfilariae which can be found in the blood as well as skin. All stages of A. reconditum are considered non-pathogenic.

Diagnosis

• Microfilariae must be distinguished from those of Dirofilaria immitis and are best found by modified Knott’s procedure.
• The direct smear is unlikely to find most infections due to the typically low numbers of microfilariae in circulation and low volume of blood utilized by the test procedure.

D. immitis

Number in blood: Few to numerous

Body movement (DS): Stationary

Cephalic end, shape: Tapered

Caudal end, shape: Straight

Body shape (K): Usually straight

Body length (K): 284–325 µm

Body width (K): 5–7.5 typically > 5.6 µm

A. reconditum

Number in blood: Few

Body movement (DS): Progressive

Cephalic end, shape: Blunt

Caudal end, shape: Usually curved or "button hooked"

Body shape (K): Usually curved

Body length (K): 237–288 µm

Body width (K): 4.5-5.6 µm

*DS = Direct Smear, K = Modified Knott test

*Pennington 1971 and Redington et al. 1977

Control and Prevention

• Routine prophylaxis whose labels include efficacy against fleas/lice should be employed to prevent infection.

Treatment

• Currently no approved products are labeled to include microfilaricidal or adulticidal efficacy against A. reconditum, prevention relies primarily on vector control.

Public Health Considerations

• There is only one report of a human subconjunctival infection by A. reconditum in Victoria, Australia.
• A. reconditum is not considered to be a zoonotic risk.

Selected References

• Huynh T, Thean J, Maini R. Dipetalonema reconditum in the human eye. British Journal of Ophthalmology. 2001 Nov 1; 85(11):1384-.
• Lindemann, B. A. (1982). The biology of experimental Dipetalonema reconditum Infections in beagles (Order No. 8225209). Available from ProQuest Dissertations & Theses Global. (303211951).
• Pennington, N. E. (1971). Arthropod vectors, cyclodevelopment and prepatent period of Dipetalonema reconditum (grassi) and the incidence of canine filariasis and ectoparasites in North-central Oklahoma (Order No. 7221970). Available from ProQuest Dissertations & Theses Global. (288064113).
• Redington BC, Jackson RF, Seymour WG, Otto GF. The various microfilariae found in dogs in the United States. GF Otto, Proceedings of the Heartworm Symposium77, KS, VM Publishing Co., Bonner Springs. 1978:14-21.