SciELO - Scientific Electronic Library Online

vol.14 número2Actividad larvicida de la toronja, Citrus paradisi (Rutaceae) sobre dos vectores del denguePrimer Registro para el Perú de Brachycaudus schwartzi (Bórner) (Hemiptera: Aphididae) índice de autoresíndice de materiabúsqueda de artículos
Home Pagelista alfabética de revistas  

Servicios Personalizados




  • No hay articulos citadosCitado por SciELO

Links relacionados


Revista Peruana de Biología

versión On-line ISSN 1727-9933

Rev. peru biol. v.14 n.2 Lima dic. 2007




Finding of Blastocystis sp. in bivalves of the genus Donax
Hallazgo de Blastocystis sp. en bivalvos del género Donax

Gregorio Pérez-Cordón1, María J. Rosales1, María del Mar Gavira, Renzo A. Valdez2, Franklin Vargas2 y Ofelia Córdova2

1 Departamento de Parasitología, Instituto de Biotecnología, Universidad de Granada (España).
2 Universidad Nacional de Trujillo (Perú).



Although commonly detected in humans, microorganisms identified as Blastocystis have also been isolated from a wide range of animals, such as primates, pigs, cattle, birds, amphibians and, less frequently, rodents and insects. In the present paper, we describe the detection of Blastocystis sp. in bivalve mollusks of the genus Donax from the Peruvian northern coast. This finding extends the host range of this pathogen, opening the possibility of Blastocytis transmission to human beings by marine mollusks.

Keywords: Blastocystis, Donax, Peru, Trujillo.



Aunque es detectado generalmente en seres humanos, los microorganismos identificados como Blastocystis han sido aislados de un amplio rango de hospedadores, tales como primates, cerdos, ganado, aves, anfibios y menos frecuentemente roedores e insectos.En el presente trabajo, se describe la detección de Blastocystis sp. en bivalvos del género Donax de la costa norteña peruana. Este hallazgo amplía el espectro de hospedadores para este enteropatógeno y abre la posibilidad de considerar la posible transmisión de Blastocystis en el hombre a partir de moluscos marinos.

Palabras clave: Blastocystis, Donax, Perú, Trujillo.



Blastocystis hominis is one of the most common protozoan parasites of the human intestinal tract (Windsor et al.2002). Although many symptomatic cases, without any other detected causative agent, have been reported in many countries, Blastocystis infections are very common in many healthy people without any symptoms. Therefore, the pathogenic potential of this parasite remains controversial (Boreham and Stenzel, 1993; Tan, Singh and Yap, 2002).

Considered and classified for a long time as a yeast (Zierdt, 1978), classified Blastocystis hominis in the subphylum Sporozoa, suborder Blastocystina and more recently in the subphylum Sarcodina (Zierdt, 1988). In studies carried out by Johnson, Thanou, Boreham and Baverstock (1989), with the ribosomal RNA of this organism, they neither found similarity with Saccharomyces nor sporozoans, suggesting that Blastocystis is not related to those groups.

From molecular epidemiology studies and traditional epidemiology results from family members and small communities, the fecal-oral route is considered the main transmission route for Blastocystis hominis infections in humans. Circumstantial evidence of several zoonotic strains identified from a wide range of mammals and birds suggests that transmission can occur between animals and humans (Doyle et al., 1990). This route is also suggested because animal handlers show a high infection level by B. hominis (Salim et al., 1999), Blastocystis has previously been isolated from a wide range of animals, such as primates, pigs, cattle, birds, amphibians, and less frequently, rodents and insects (Boreham and Stenzel, 1993; Tan, Singh and Yap, 2002).

Several new species have been differentiated from B. hominis, but without a major confirmation by using molecular analysis, B. hominis defines the parasite isolated from humans and Blastocystis sp. the parasite isolated from animal hosts. In the present paper, we describe the finding of Blastocystis sp. in bivalves of the genus Donax.

As a part of a study on human intestinal parasites in mollusks, 637 bivalves of the genus Donax were acquired from a popular market in the Trujillo city (North of Peru), and transported to the Institute of Microbiology and Tropical Parasitology in National University of Trujillo, Peru. All the bivalves were opened by valve separation and the feces of 100 specimens were removed by using a Pasteur pipette and stored in 2% K2Cr2O7. The body of these specimens and all other specimens were stored in 70% alcohol for possible future studies by PCR. The valves were washed by using saline physiologic solution (0.85% NaCl). The resulting liquid from washing in the saline solution was centrifuged at 3000 rpm and the pellet was used to concentration by using Willis method (Willis, 1921), prior to optical microscope observation. Half the feces from the total volume in K2Cr2O7 were observed with an optical microscope by direct examination and the rest was concentrated by using the Ritchie technique (Ritchie, 1948). The microscopic observation of feces and the suspension from the washed valves showed the presence of stages of Blastocystis sp. but the latter with less concentration of Blastocystis (Fig.1).


The stages seen were espherical cysts with a variable diameter (5-30 µm), with a central vacuole surrounded by a cytoplasm ring that contained several nuclei. However, according to some researchers the vacuolar stage is also commonly observed (Requena-Certad et al; 1999). The finding of Blastocystis sp. in bivalves of the genus Donax increases the known host range of this parasite. It is the first report of Blastocystis in marine mollusks. The differentiation of new species of Blastocystis should be confirmed by using molecular studies, so we could not name this finding as a new species without the pertinent analysis. However, we can affirm that Blastocystis is present in bivalves frequently consumed not only in Peru but also in many areas worldwide. This adds a possible link to the epidemiological chain of this pathogen. The fecal-oral route is considered to be the main mode of transmission, but food-borne and waterborne transmission of Blastocystis via untreated water of poor sanitary conditions have also been suggested (Kain et al; 1987).

These bivalves normally are prepared by using high temperature prior to being consumed, but the manipulation of the bivalves by handlers and other people may pose a risk of transmission, as the during the opening of the bivalves may result in direct contact with the mollusks´ feces. Without clear diagnostic features that allow the differentiation of Blastocystis spp, we do not know the precise number of species that could infect humans from zoonotic transmission. This presents challenges to our understanding of the epidemiology of Blastocystis and its implications for public health.

Literature cited

Boreham, P. F. L., and D. J. Stenzel. 1993. Blastocystis in humans and animals: morphology, biology, and epizootiology. Adv. Parasitol. 32:1_70.

Doyle, P. W., M. M. Helgason, R. G. Mathias, and E. M. Proctor. 1990. Epidemiology and pathogenicity of Blastocystis hominis. J. Clin. Microbiol. 28:116_121.

Johnson, A.M., Thanou, A., Boreham, P.F.L. and Baverstock, P.R. 1989. Blastocystis hominis: phylogenetic affinities determined by rRNA sequence comparison. Experimental Parasitology 68:283-288.

Kain K, Noble M, Freedman H, Barteluk R. Epidemiology and clinical features associated with Blastocystis hominis infection. Microbiol Infect Dis 1987; 8: 235-44.

Ritchie LS. An ether sedimentation technique for routine stool examination. Bull US Army Med Dept 1948; 8:326.

Salim, H. R., Suresh Kumar, G., Vellayan, S., Mak, J.W., Khairul Anuar, A., Init, I., Vennila, G.D., Saminathan, R. and Ramakrishnan, K.. 1999. Blastocystis in animal handlers. Parasitology Research 85:1032-1033

Tan, K.S.W., Singh, M., Yap, E.H. 2002. Recent advances in Blastocystis hominis research: hot spots in terra incognita. International Journal for Parasitology 32:789-804.

Willis, H.H. A simple levitation method for the detection of hookworm ova. Med. J. Aust., v.11, p.375-376, 1921.

Windsor JJ, Macfarlane L, Hughes-Thapa G, Jones SKA, Whiteside TM 2002. Incidence of Blastocystis hominis in faecal samples submitted for routine microbiological analysis. Br J Biomed Sci 59:154_157.

Zierdt CH. 1978. Blastocystis hominis, an intestinal protozoan parasite of man. Public Health Laboratory 36:147-161.

Zierdt CH. 1988. Blastocystis hominis, a long misunderstood intestinal parasite. Parasitology Today 4:15-17.


Address for correspondence: Gregorio Pérez Cordón, N/Sto. Angel Guarda.Blq5-BajoA, CP:41010-Seville (Spain)
E-mail Gregorio Pérez-Cordón:

Presentado: 29/01/2007
Aceptado: 16/09/2007