Uncinaria stenocephala

Adults of the nematode Uncinaria stenocephala live in the small intestine of dogs.  In Canada this hookworm is more common in northern areas than further south.  The life cycle is direct.  Third-stage larvae are infective and generally gain access to the host by ingestion, following which they undergo a mucosal migration.  Uncinaria can also use small mammal paratenic hosts.  It is generally considered to be non-pathogenic in dogs, although a dermatitis and protein losing enteropathies are possible. Uncinaria stenocephala is unknown.

Phylum: Nematoda
Class: Secernent
Order: Strongylida
Superfamily: Ancylostomatoidea
Family: Ancylostomatidae

Uncinaria stenocephala is the northern hookworm of dogs. It is related to the other hookworms of dogs (A. caninum, A. braziliense and A. ceylanicum), and to the hookworms of cats (A. tubaeforme and A. ceylanicum) and of people (A. duodenale and Necator americanus). The adult parasites and the eggs of these various hookworm species are morphologically similar, and the life cycles and pathology share many features. Some species of hookworm are able to infect several species of host, including people.

Adult U. stenocephala are up to approximately 15 mm in length and have a prominent buccal capsule, the opening into which has two cutting plates , one on each side of its ventral aspect. The exact structure of the buccal capsule is important in distinguishing between the various hookworm species.

Eggs measure approximately 65 to 80 µm by 40 to 50 µm, and are oval with a thin, smooth shell. When freshly passed, each egg contains a few cells grouped together - a "morula". Eggs of U. stenocephala are slightly larger than those of A. canium, and this is the basis for differentiation of the two parasites on fecal examinations.

Uncinaria stenocephala is common in dogs and other canids, but rare in cats and other felids, in cooler areas of the world, including northern Canada. In a recent national study of shelter dogs, prevalence was 3% nationally, 4% in western Canada (Villeneuve et al., 2015).  This hookworm is relatively common in arctic fox, red fox, coyote, and wolves in Canada.

The life cycle of U. stenocephala is direct. Eggs are passed in feces of a canine definitive host. In the environment, a first-stage larva develops within each egg. The larva then hatches and develops to the infective third stage - within 4-8 days under ideal conditions (temperatures greater than 7.5 C). Dogs generally become infected by ingestion of infective larvae, followed by a mucosal migration. The infective larvae of Uncinaria can penetrate the skin, but only very rarely develop into adults in the intestine. Dogs can also become infected by ingesting third stage larvae of Uncinaria in the tissues of small mammal paratenic hosts. Ther pre-patent period is 2-3 weeks. Pre-natal and transmammary infections are not thought to occur.

Eggs and larvae of Uncinaria stenocephala are more cold tolerant than those of Ancylostoma caninum, the southern hookworm of canids. 

Environmental stages of hookworms are not particularly robust (compared to other parasites) and do best in warm, moist environmental conditions that support the survival and rapid development of the infective larvae. Sub-optimal hygiene also favours the parasite by exposing susceptible dogs to these larvae. For animals in kennels or shelters, where host density enhances opportunities for transmission, effective treatments and maintaining a clean environment are key elements of all control programs.

Uncinaria stenocephala appears to be only mildly pathogenic, although large numbers of adults plug-feeding in the mucosa can cause protein losing enteropathy, mucousy diarrhea, and poor growth.  Although percutaneous invasion is rare dermatitis associated with infective larvae of Uncinaria has been reported in Canada. Adult animals with low intensity infections may be entirely subclinical.

Detection of Uncinaria stenocephala eggs (typical thin-walled, morulated, strongyle-type) in feces by centrifugation-flotation is often helpful, but in areas where A. caninum also occurs the eggs of the two genera cannot always be differentiated. Eggs of Uncinaria measure approximately 70-90 by 35-60 µm, whereas those of A. caninum measure approximately 50-80 by 30-60 µm but there is overlap in this size range.  When geographic clues are not helpful, PCR is necessary to definitively distinguish the two genera in dogs.   Note that fecal samples should be fresh, as larvae may begin to develop rapidly within the eggs, especially in warmer temperatures.  Newer coproantigen tests may detect hookworm infection even in the pre-patent period. For ventral dermatitis cases, larvae of Unicinaria can be recovered by deep skin scraping or biopsy, and distinguished from those of the free living nematode Pelodera strongyloides and the hookworm Ancylostoma caninum by their filariform pharynx and size respectively.

Several products are marketed in Canada that are effective against the stages of Uncinaria stenocephala in the GI lumen including benzimidazoles and macrocyclic lactones. Because of the low pathogenicity of U. stenocephala, however, specific treatment or control measures are rarely recommended. These hookworms can be problematic in kennels and shelters (largely due to rapid re-infection from the environment), and control should include enhanced environmental hygiene and improved management, as well as targeted treatment and repeat testing to monitor treatment efficacy.  Anthelmintic resistance, which is an increasing problem with Ancylostoma caninum, has not yet been described for Uncinaria stenocephala.

Uncinaria stenocephala is not thought to be a significant zoonosis

Chu, S., Myers, S. L., Wagner, B., & Snead, E. C. (2013). Hookworm dermatitis due to Uncinaria stenocephala in a dog from Saskatchewan. Canadian veterinary journal 54(8), 743–747.