Rhipicephalus sanguineus (ACARI: IXODIDAE) BITING A HUMAN BEING IN PORTO ALEGRE CITY, RIO GRANDE DO SUL, BRAZIL

Abstract

We report the finding of a female brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae) on the scalp of a male patient in Porto Alegre, Rio Grande do Sul, Brazil. Human parasitism by this tick is rare and has seldomly been reported in the literature, despite its recognized importance since it can act as a vector of Rickettsia rickettsii, the agent of spotted fever.

Brown dog tick; Diagnosis; Ectoparasite; Vector-borne diseases

INTRODUCTION

The brown dog tick (or kennel tick) Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) has great medical and veterinary significance, since it is a vector and reservoir of many human and animal pathogens^1-5. Dogs are the main hosts of the adult and pre-adult parasitic stages of the tick. Adults of R. sanguineus can also feed on humans and many other mammals, such as goats, sheep, cattle, horses, wild carnivores, cats, hares and hedgehogs; pre-adult ticks have been found in shrews and many rodents^6-11.

The genus Rhipicephalus comprises 17 species that are morphologically similar and show intraspecific variations within populations whose taxonomic status is still uncertain¹². Nowadays, the molecular approach is used to investigate differences among the species of the R. sanguineus complex^13-15.

Although human parasitism by R. sanguineus is unusual, it has already been reported in different parts of the world^16-22. In Brazil, the first description of human parasitism by this species of ixodid tick was reported in 2005²³. Other cases have been recorded ever since in the country^24-27.

The ability of R. sanguineus to transmit pathogens such as Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, known in Brazil as Brazilian spotted fever (BSF), to humans is little understood^28-33. On the other hand, infestation by Rhipicephalus sanguineus (Latreille) in dogs has increased considerably in urban areas of the State of Rio Grande do Sul^34-36.

Here, we report the finding of an adult female of R. sanguineus on the scalp of an adult male patient in the city of Porto Alegre, Rio Grande do Sul, Brazil.

CASE REPORT

A 27-year-old male presented with bilateral erythematous macular inflammatory lesions, with a central bite spot, on the posterior region of the thigh (Fig. 1A). The lesions healed spontaneously. A week later, he reported other, similar lesions and minor allergic reactions including redness and swelling in the right ear (Fig. 1 B), face (Fig. 1 C), right thigh (Fig. 1 D), neck, and right hand. Some days later, the patient found a tick on his scalp. He consulted a physician, and no other remarkable findings were seen. Based on the skin lesions and the presence of the tick, serology tests for Rickettsia and Borrelia were requested, and a presumptive treatment for rickettsia with doxycycline for 21 days was started. The serology tests were negative.

Fig. 1
- A. The patient's skin lesions in the posterior area of the thigh; B. Right ear; C. Face; D. Right thigh.

While awaiting the serological results, the patient sent the tick specimen to the Parasitology Laboratory at ICBS-UFRGS for identification. The tick was identified as a female brown dog tick, Rhipicephalus sanguineus (Fig. 2A, B), based on the characteristics described by Guimarães et al.³⁷ The patient has improved and remains asymptomatic.

Fig. 2
- Rhiphicephalus sanguineus: FEMALE - A. Dorsal view; B. Ventral view.

DISCUSSION

Dantas-Torres & Otranto⁶ stated that some populations presently assigned to R. sanguineus in different parts of the world could belong to different species, and that this possibility may have been overlooked by taxonomists. However, it is also possible that this wide geographical distribution can be attributed to the adaptability of this tick species to different hosts and climate conditions.

Borsoi & Serra-Freire²⁸ found that R. sanguineus was the dominant species in some communities in the State of Rio de Janeiro. People in daily contact with dogs parasitized by R. sanguineus could be included in the risk group for this type of parasitism^24,25. These conditions could increase the risk of transmission of R. rickettsii to humans in Brazil. Future studies are needed to determine the incidence of R. rickettsii in local populations of R. sanguineus^29,30,39.

Information on human parasitism by R. sanguineus in Brazil is sparse. In 2005, Dantas-Torres et al.²³ provided the first, brief description of human parasitism by this species of tick in Brazil. In the following year, Dantas-Torres et al.²⁴ investigated the species of ectoparasites in domestic dogs from the metropolitan region of Recife, Pernambuco State, and reported that four dog owners were found to be parasitized by ticks identified as R. sanguineus. These were the first four cases of human parasitism by this tick species in Brazil. Louly et al.²⁵ described the first case of human parasitism by R. sanguineus in the State of Goiás.

Several species of ticks are vectors of viruses, protozoa and rickettsia that cause human diseases^4,30,40. This reinforces the need to increase the knowledge of the parasitic relationship between ticks and humans, as well as for the continuous implementation of control measures against this parasite^{17,29,31,32,41}.

In Brazil, a detailed study of the factors leading to human parasitism by ticks is needed, since most studies until now have examined only the species distribution and occurrence.

Brazilian spotted fever (BSF) is an infectious, febrile, and acute disease, with variable severity, which usually has an endemic character. This disease can be difficult to diagnose, especially in the early stages. Because it is multi-systemic, spotted fever can follow different clinical courses, ranging from the classical picture to atypical forms without exanthema. If not treated properly, mortality in the most severe cases reaches 80%³⁸.

This is the first report of a R. sanguineus tick biting a human being in Porto Alegre. In the case reported here, we presume, based on the skin lesions seen in the patient, that the female tick made several attempts to attach without success.

The public-health authorities must evaluate the incidence of R. sanguineus in dogs from urban areas, improving the monitoring of the distribution of these dogs and their contact with humans³⁴. Future control attempts must consider the limited knowledge of the tick behavior and other biological parameters in the State of Rio Grande do Sul.

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Publication Dates

• Publication in this collection
  2016

History

• Received
  25 May 2015
• Accepted
  28 Sept 2015