Human Oestrus sp. infection, Canary Islands.

To the Editor: Myiasis due to Oestrus ovis is a well known zoonosis that affects a variety of animals. Human myiasis has also been described and affects mainly persons in rural areas such as shepherds (1) and farmers (2). Although this disease has been reported in both humans and mammals in Spain (3,4), no human case has been described on the Canary Islands. We describe what we believe is the first confirmed case on the islands and discuss the potential utility of serologic diagnosis for this disease.

A 55-year-old farmer from the island of El Hierro, with a medical history of hypercholesterolemia, Q fever, and murine typhus, but currently not being treated, consulted a physician in August 2005 concerning a wormlike sensation in his nose and sinuses that had lasted 2 days. Three days before noticing this sensation, he had been working in his neighbor's barn, when he noticed that a passing fly "dropped" something in his nose. He also reported sneezing and watery rhinorrhea. These symptoms were self-treated with nasal anticongestants, which provided temporary relief. He finally sought medical attention when a severe cough developed and the wormlike sensation extended to his throat.

On physical examination, the patient's vital signs were normal, although a turbinate hypertrophy and mild redness of the throat were noted. No foreign objects or insects were seen on otorhinolaryngologic examination. The patient's blood count showed 8,480 leukocytes/[micro]L with 6.1% (520/[micro]L) eosinophils. Because of his stated symptoms, myiasis was suspected, and symptomatic treatment was started, consisting of antihistamines, nasal anticongestants, cough suppressants, and asphyxiant methods, i.e., swallowed olive oil. The patient was monitored closely and had complete remission of his symptoms after 6 days. No relapse has occurred.

In the meantime, we discovered that a serologic test for O. ovis was available (5). We requested and obtained a convalescent-phase serum sample from the patient on day 14 of his illness. Blood was also obtained from different "healthy" animals in the patient's neighborhood, including 2 dogs, 4 sheep, and 5 goats. This serologic assay had not previously been used in testing humans. Excretory and secretory antigens from O. ovis L2 (OL2ES) were obtained as previously described (6), and samples were analyzed by an immune enzymatic assay technique (7). Appropriate testing with different dilutions of the antigens, sera, and immunoconjugates was conducted. Immunoglobulin G (IgG) was detected in the patient, sheep, goats, and dogs following a similar protocol. OL2ES concentrations were 1, 1, 3, and 5 [micro]g/mL, respectively. Serum samples were diluted 1:100 for the patient and the dogs and 1:50 for the goats; immunoconjugates were diluted 1:1,500 for all species. O. ovis IgG was found in the patient's sera, as well as in sera of the 2 dogs, 2 of 4 sheep, and all 5 goats (Table).

Human infection by O. ovis is generally considered to be an accidental occurrence (8). This case confirms, however, that myiasis caused by O. ovis must be considered in the differential diagnosis of a patient with typical symptoms and eosinophilia. Most farmers in this area have reported similar symptoms. Most, however, do not seek medical attention because they prefer to use homemade remedies, such as topical oil.

The diagnosis of oestrosis is usually made by direct visualization of the larvae, since the most frequent symptoms are pharyngeal myiasis and ophthalmomyiasis. Immunodiagnostic methods, however, could be a viable alternative to the clinical examination when no larvae are directly seen but a high degree of suspicion exists. The ELISA was noted to have a sensitivity of 96.1% and a specificity of 55.8% (positive predictive value of 86.7% and negative predictive value of 82.8%) in various investigations made with sheep and goats (6).

Although allergic symptoms are frequent in animals, the pathophysiologic process seems to be different in humans (8). Nevertheless, other authors have also described coughing and sneezing (1), probably attributable to irritation of the mucosa. In animals, a primary peak in eosinophil numbers has been noted 4 days after infection with a primary increase 48 hours after infection (9). In humans this pattern has not been described, but we did note a mild eosinophilia that disappeared after the patient recovered from his symptoms.

Outcome of the disease in humans is generally benign. Treatment includes removal of the larvae and, in some cases, prevention of local infections. Ivermectin has also been found useful in animal and human infections (10).

To our knowledge, this is the first case of human oestrosis on the Canary Islands, as well as the first human case described with eosinophilia. Physicians should be aware of the possibility of this disease in our region and of the fact that a serologic test is available for its diagnosis.

References

(1.) Masoodi M, Hosseini K. The respiratory and allergic manifestations of human myiasis caused by larvae of the sheep bot fly (Oestrus ovis): a report of 33 pharyngeal cases from southern Iran. Ann Trop Med Parasitol. 2003;97:75-81.

(2.) Fathy FM, El-Barghathi A, El-Ahwal A, El-Bagar S. Study on human ophthalmomyiasis externa caused by Oestrus ovis larva, in Sine-Libya: parasite features, clinical presentation and management. J Egypt Soc Parasitol. 2006;36:265-82.

(3.) Beristain X, Alkorta M, Egana L, Lacasta A, Cilla G. Nasopharyngeal myasis by third stage larvae of Oestrus ovis. Enferm Infecc Microbiol Clin. 2001 ; 19:86-7.

(4.) Lucientes J, Ferrer-Dufol M, Andres MJ, Peribanez MA, Gracia-Salinas MJ, Castillo JA. Canine myiasis by sheep bot fly (Diptera: Oestridae). J Med Entomol. 1997;34:242-3.

(5.) Sanchez-Andrade R, Romero JL, Suarez JL, Pedreira J, Diaz P, Arias M, et al. Comparison of Oestrus ovis metabolic and somatic antigens for the immunodiagnosis of the zoonotic myasis oestrosis by immunoenzymatic probes. Immunol Invest. 2005;34:91-9.

(6.) Suarez JL, Scala A, Romero JA, Paz-Silva A, Pedreira J, Arias M, et al. Analysis of the humoral immune response to Oestrus ovis in ovine. Vet Parasitol. 2005;134: 153-8.

(7.) Scala A, Paz-Silva A, Suarez JL, Lopez C, Diaz P, Diez-Banos P, et al. Chronobiology of Oestrus ovis (Diptera: Oestridae) in Sardinia, Italy: guidelines to chemoprophylaxis. J Med Entomol. 2002;39:652-7.

(8.) Dorchies P. Comparative physiopathology of Oestrus ovis (Linne 1761) myiasis in man and animals. Bull Acad Natl Med. 1997;181:673-84.

(9.) Yacob HT, Jacquiet P, Prevot F, Bergeaud JP, Bleuart C, Dorchies P, et al. Examination of the migration of first instar larvae of the parasite Oestrus ovis (Linne 1761) [Diptera: Oestridae] in the upper respiratory tract of artificially infected lambs and daily measurements of the kinetics of blood eosinophilia and mucosal inflammatory response associated with repeated infection. Vet Parasitol. 2004; 126:339-47.

(10.) Macdonald PJ, Chan C, Dickson J, Jean-Louis F, Heath A. Ophthalmomyiasis and nasal myiasis in New Zealand: a case series. N Z Med J. 1999;112:445-7.

Marion Hemmersbach-Miller, * ([dagger]) Rita Sanchez-Andrade, ([double dagger]) Alicia Dominguez-Coello, ([section]) Adnan Hawari Meilud, * Adolfo Paz-Silva, ([double dagger]) Cristina Carranza, ([paragraph]) and Jose-Luis Perez-Arellano ([paragraph])

* Hospital Ntra. Sra. de los Reyes, Valverde. El Hierro, Spain; ([dagger]) Hospital San Roque Maspalomas, Gran Canaria, Spain; ([double dagger]) Santiago de Compostela University, Lugo, Spain; ([section]) Veterinarian of the Cooperativa de Ganaderos de El Hierro, El Hierro, Spain; and ([paragraph]) University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain

Address for correspondence: Jose Luis Prrez-Arellano, Departamento de Ciencias Medicas y Quirurgicas, Centro de Ciencias de la Salud. Universidad de las Palmas de Gran Canaria, 35080 Las Palmas de Gran Canaria, Spain; email: [e-mail]

Table. Results and interpretation, Oestrus sp. infection,
Canary Islands * ([dagger])

                 Human                               Dogs

   OD       Interpretation          OD          Interpretation

  0.658        Positive            0.677           Positive
                                   0.824           Positive

                 Sheep                               Goats

   OD       Interpretation          OD          Interpretation

  0.639        Positive            0.838           Positive
  0.685        Positive            0.535           Positive
  0.226        Negative            0.594           Positive
  0.187        Negative            0.673           Positive
                                   0.622           Positive

* Results are expressed as optical density (OD), and interpretation
(positive/negative) was made by using the following cut-offs: in
sheep: 0.369 (0.1718 + 3 x 0.066); goats: 0.406 (0.211 + 3 x
0.065); human 0.32 (0.17 + 3 x 0.049); dogs: 0.493 (0.37 + 3 x 0.041).

([dagger]) One sample of positive and negative control samples was
added to each plate. Sheep and goat sera from animals with a known
history of O. ovis exposure were used. When positive sera were not
available (human and dogs), we used only negative sera, and the
cut-off was estimated as the mean OD of the negative sera plus 3
SDs (7).