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Trombiculiasis: clinical contribution

European Journal of Dermatology. Volume 15, Number 6, 495-6, November-December 2005, Clinical report

Summary

Author(s) : Fabrizio Guarneri, Antonio Pugliese, Elisabetta Giudice, Claudio Guarneri, Salvatore Giannetto, Biagio Guarneri , Dipartimento di Medicina Sociale del Territorio, sezione di Dermatologia, University of Messina, ItalyFax: (+39) 090 2927691., Dipartimento di Scienze Mediche Veterinarie, University of Messina, Italy.

Summary : Neotrombicula autumnalis is an arthropod usually living in the soil, except for the short period of the larval stage when it becomes a real parasite of warm-blooded hosts. We present a case of human trombiculiasis, which is unusual because of the parasite transmission from animals to humans, as in a typical synanthropic dermatosis.

Keywords : neotrombicula autumnalis, trombiculiasis, synanthropic dermatosis

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ARTICLE

Auteur(s) : Fabrizio Guarneri¹, Antonio Pugliese², Elisabetta Giudice², Claudio Guarneri¹, Salvatore Giannetto², Biagio Guarneri¹

¹Dipartimento di Medicina Sociale del Territorio, sezione di Dermatologia, University of Messina, ItalyFax: (+39) 090 2927691.
²Dipartimento di Scienze Mediche Veterinarie, University of Messina, Italy

accepté le 2 Février 2005

Neotrombicula autumnalis is an organism belonging to the phylum Arthropoda, class Arachnida, subclass Acarina. Unlike many phylogenetically related species, Neotrombicula autumnalis parasitizes animals only in its larval stage.The life cycle of Neotrombicula autumnalis starts from eggs, which, after deposition on soil, hatch in about ten days as six-legged larvae. Larvae then climb onto warm-blood hosts (either humans or animals) and feed for 2-10 days, using chelicerae to inject lytic enzymes in the upper layers of the skin and, subsequently, to ingest digested cells. In this phase, larvae are reddish-orange, 0.2-0.4 mm long.After this short period in the host, larvae return to the soil, where in 5-6 weeks they develop into eight-legged nymphae, very similar to the adult stage of the parasite, which they will quickly reach. Both nymphae and adults are host-independent and live in the soil, feeding on plant fluids or small insects.Similar to other mites, Neotrombicula autumnalis prefers a heated and humid environment. Depending on climatic conditions, one to five complete life cycles can take place in a single year. Adults usually deposit eggs in spring and summer and, consequently, larvae are particularly abundant in late summer and autumn; the parasite is inactive in winter. In certain geographical areas, heavy infestations are frequently observed [1, 2].As mentioned above, human and animal disease caused by Neotrombicula autumnalis is due to larvae: consequently, trombiculiasis mostly frequent occurs between late August and late October, and mainly affects subjects who live in the countryside. Since larvae live in the soil and have no wings, they climb on body parts of the host which are in direct contact with the soil. The animals most frequently infested are small rodents and dogs, but several different species such as domestic animals, birds, and reptiles are not spared. Farmers are at particular risk, especially if they walk barefoot.When the parasite climbs onto its host, it moves on the surface to find areas where skin is thinner or where clothing fits tightly. In humans, the preferred feeding zones are ankles, armpits, popliteal fossae, antecubital fossae, lower half of legs, groin, or around the belt line, waistline, under a girdle.Insertion of chelicerae in the skin is painless. Clinical skin manifestations of Neotrombicula autumnalis consist of severe itching and skin inflammation of variable degrees and are due to the digestive enzymes of the parasite. If untreated, itch can persist for more than a week, and cause violent scratching (in animals, also biting) with consequent superinfection.In animals, massive infestations may cause neurological involvement, with paresis of the posterior limbs, asthenia, limping and continuous headshaking.Moreover, recent studies [3] showed that Neotrombicula autumnalis could be a vector for some infections: Ehrlichia phagocitophila was detected in 10% of the larvae before their contact with hosts, suggesting transovarian transmission of bacteria.

Case report

Two brothers, aged 38 and 42, came to our observation in October 2002, because of suspicious allergic urticaria. They reported the presence of intensely itching wheals on the trunk and limbs, that had appeared 3 days earlier. Clinical examination showed, in both brothers, wheals, often with a raised, whitish, hard area; some wheals contained pus. Most skin lesions were abdominal, particularly in areas subjected to tighter contact with clothes (elastic bands, belt); scratching-related lesions were also present ( (figure 1) ). Acariasis was suspected, so that we questioned the patients more carefully. One of them reported that, three days before the onset of the symptoms, he went hunting in a forest in the Nebrodi mountains (Messina, Sicily, Italy), with two female Italian sleuthhounds, aged 5 and 7 years. The younger dog belonged to his younger brother, who had remained at home that day and the subsequent seven days because of fever. Back home, the dogs were restless because of intense itching. The two dogs got worse on the two following days, so a veterinarian was consulted.

Clinical examination of tegumentary elements of the two dogs revealed a vast erythematous dermatitis, with a vesicular and papular-crusty eruption. This markedly itchy eruption was localized particularly in areas with thin and glabrous skin, like the ventral portion of the abdomen, thighs, limbs, chin, and ears; desquamation, secondary alopecia, scratching-related lesions and several ticks were also present. Several small reddish-orange organisms, rapidly moving on the skin and on objects in contact with the skin, suggested the diagnosis of massive trombiculiasis to us. To confirm our clinical suspicion, we obtained some specimens from supraorbital areas, where concentration of the parasites was greater. Microscopic examination, after addition of mineral oil, showed 300-400 μm long, reddish-orange mites, characterized as follows:

– three pairs of long legs, carrying three strong claws (outer paired and medial), covered with several plumose setae;
– a small pentagonal sclerotized shield, with five ciliated setae (four angular and one anterior) and two sensilla, sensorial flagella, and paired eyes by the shield side;
– the feeding apparatus or gnatostoma with paired strong hooked chelicerae and paired segmented palps on sides: the second-last segment (palpal tibia) carrying a triple forked claw and the last one (palpal tarsus) covered with ciliated setae;
– a naked galeal seta.

On the basis of the above characteristics, parasites were identified as larvae of Neotrombicula autumnalis [6, 7].

The patient who had gone hunting complained that he had already suffered from similar clinical manifestations the year before, precisely the day after having hunted in the same forest; he thought that the symptoms were due to a “reddish pollen” falling from beech trees.

We prescribed a treatment with oral antihistaminic, topical steroids, and antibiotic creams for secondarily infected lesions. We also recommended to wash, at a minimum of 55 °C, garments and any material which could have been in contact with either brother or their animals.

For the dogs, the veterinary prescribed anti-parasite therapy with fipronil 0.25%, oral antihistaminic and local treatment with pyrethroids and phosphoric esters.

After a week of treatment, patients and dogs experienced complete healing of the cutaneous lesions and regression of itching. Both brothers were doing well at their last visit in December 2002.

Discussion

Human infestation by Neotrombicula autumnalis, although rarely reported in the literature, has a not-negligible incidence. Our observation points out a particular and often neglected way of transmission of the parasites. Since one brother had no direct contact with infested soil or plants, it is very likely that infestation was caused by his brother and/or by the dogs. The concentration of the lesions on the abdomen and thighs suggests to us the second hypothesis, considering that the dogs were frequently allowed to sit on the legs of our patients.

Based on our observation, human infestation from Neotrombicula autumnalis can then be considered, at least in part, a synanthropic dermatosis. This possibility is, in our opinion, currently underestimated, but should be appropriately considered for differential diagnosis in clinical practice.

In addition, the possible neurological involvement documented in massively infested animals [4, 5], and the preliminary data on the possible role of Neotrombicula autumnalis as a vector of pathogens, suggest that trombiculiasis is a parasitosis that deserves greater consideration by both physicians and veterinarians. The use of effective and well tolerated repellents on animals [8] and on clothes and limbs [9, 10] is recommended before hiking in areas “at risk”, particularly during periods of more intense larval activity.

References

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2 Vater G. Harvest mite Neotrombicula autumnalis in the Leipzig area. Angew Parasitol 1981; 22: 32-8.

3 Fernandez-Soto P, Perez-Sanchez R, Encinas-Grandes A. Molecular detection of Ehrlichia phagocitophila genogroup organism in larvae of Neotrombicula autumnalis (Acari: Trombiculidae) captured in Spain. J Parasitol 2001; 87: 1482-3.

4 Kampen H, Scholer A, Metzen M, et al. Neotrombicula autumnalis (Acari, Trombiculidae) as a vector for Borrelia burgdorferi sensu lato? Exp Appl Acarol 2004; 33: 93-102.

5 Mair TS. Headshaking associated with Trombicula autumnalis larval infestation in two horses. Equine Vet J 1994; 26: 244-5.

6 Prosl H, Rabitsch A, Brabenetz J. Trombiculid mite–Neotrombicula autumnalis (Shaw 1790)–in veterinary medicine. Nervous systems in dogs following massive infestation. Tierarztl Prax 1985; 13: 57-64.

7 Brennan JM, Jones EK. Key to the chiggers of North America with synonymic notes and descriptions of two new genera (Acarine: Trombiculidae). Ann Entomol Soc Am 1959; 52: 7-16.

8 Giannetto S, Canestri Trotti G. Trombicula (Neotrombicula) autumnals (Acarina: Trombiculidae) in Turdus musicus (Passeriformes) in Sicily. Atti della Società Italiana delle Scienze Veterinarie 1995(XLIX): 761-2.

9 Nuttall TJ, French AT, Cheetham HC. Proctor FJ Treatment of Trombicula autumnalis infestation in dogs and cats with a 0.25 per cent fipronil pump spray. J Small Anim Pract 1998; 39: 237-9.

10 Breeden GC, Schreck CE, Sorensen AL. Permethrin as a clothing treatment for personal protection against chigger mites (Acarina: Trombiculidae). Am J Trop Med Hyg 1982; 31: 589-92.

11 Frances SP, Yeo AE, Brooke EW, Sweeney AW. Clothing impregnations of dibutylphthalate and permethrin as protectans against a chigger mite, Eutrombicula hirsty (Acari: Trombiculidae). J Med Entomol 1992; 29: 907-10.