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Human gnathostomiasis, which is endemic in Mexico, is a worldwide health concern. It is mainly caused by the consumption of raw or insufficiently cooked fish containing the advanced third-stage larvae (AL3A) of Gnathostoma species. The diagnosis of gnathostomiasis is based on epidemiological surveys and immunological diagnostic tests. When a larva is recovered, the species can be identified by molecular techniques. Polymerase chain reaction (PCR) amplification of the second internal transcription spacer (ITS-2) is useful to identify nematode species, including Gnathostoma species. This study aims to develop a duplex-PCR amplification method of the ITS-2 region to differentiate between the Gnathostoma binucleatum and G. turgidum parasites that coexist in the same endemic area, as well as to identify the Gnathostoma larvae recovered from the biopsies of two gnathostomiasis patients from Sinaloa, Mexico. The duplex PCR established based on the ITS-2 sequence showed that the length of the amplicons was 321 bp for G. binucleatum and 226 bp for G. turgidum. The amplicons from the AL3A of both patients were 321 bp. Furthermore, the length and composition of these amplicons were identical to those deposited in GenBank as G. binucleatum (accession No. JF919679), corroborating our previous morphological finding that G. binucleatum is the etiological agent for human gnathostomiasis in the endemic area of Sinaloa, Mexico.

Several coastal lagoons and estuaries in Mexico receive untreated domestic and industrial discharges which contain complex mixtures of contaminants. In order to assess the effects of chemical contamination, we used the White mullet (Mugil curema) as biological indicator. We worked in two estuaries located in Northwest Mexico: Urias (highly polluted) and Teacapan (less polluted, therefore used as reference site). We measured several endpoints at different levels of biological organization: vitellogenin transcription in males as biomarker of estrogenic contamination, as well as reproductive, morphological (deformities), morphometric, and meristic parameters. Total RNA was isolated from the liver, and a partial sequence of the mullet vitellogenin gene was obtained; gene expression was analyzed by quantitative PCR. At the same time, gonad samples were analyzed by histologic techniques to determine sex ratios and the reproductive cycle stage. The reproductive season was detected from February to June in both sites, but the gonadosomatic index was consistently higher in Teacapan. Sex ratios were female-biased in both estuaries, and one intersex gonad and several malformations were found in fish from Urias. Vitellogenin gene transcription in males was detected in both sites, although gene expression was slightly higher in Urias. The results obtained in this study indicate that biological effects of contamination are evident in fish, environmental estrogens may be present in both estuaries, and the white mullet is useful as biological indicator to identify and characterize environmental stressors in tropical coastal ecosystems.

Gnathostomiasis is now recognized as a zoonosis with a worldwide distribution. In the Americas, it is caused by the third-stage larvae of Gnathostoma binucleatum and in Asia mainly by G. spinigerum. The availability and preparation of specific antigens are among the main obstacles for developing reliable immunodiagnostic tests. In this study, six immunodominant peptides were identified and characterized from G. binucleatum, somatic antigens (AgS: 24, 32, and 40 kDa) and excretory-secretory antigens (AgES: 42, 44, and 56 kDa) by two-dimensional immunoblot analysis. Among those immunodominant peptides, two AgS spots were characterized by mass spectrometric analysis (32 kDa; pI 6.3 and 6.5) and identified as type 1 galectins. In accordance with this finding, a fraction of AgS exhibited affinity to lactose and displayed a 100% specificity and sensitivity for the diagnosis of human gnathostomiasis.

Follicular apoptosis in the tropical mussel Mytella strigata was assessed in three coastal lagoons located in the southern Gulf of California, Mexico. Mussels were collected from three coastal lagoons associated with different scenarios of anthropogenic stress during one year. The gonad of each mussel was dissected, weighed, and sampled for histology and apoptosis analysis by TUNEL labeling. Two apoptotic indices were used: the apoptotic index of cells (AIC) based on the number of follicular cells in apoptosis in one thousand cells counted per gonad, and the apoptotic index of follicles (AIF) based on the number of follicular cells per follicle per gonad. Both indices showed high association with each other for all developmental stages, although AIF seemed to better discriminate among sites. Higher AIF and AIC were observed at the Urias Estuary (1.6 and 1.5 respectively) ranked as highly polluted, followed by Ensenada del Pabellon (0.82 and 0.95 respectively), ranked as moderately polluted, and the Teacapan Estuary (0.57 and 0.76 respectively) ranked as slightly polluted. Our data indicate that the apoptotic index in tropical mussels could be a useful indicator of environmental stress in coastal ecosystems; however, the ecological relevance of follicular apoptosis in polluted environments needs further investigation.

The relationship between parasites and environmental stress were studied in two tropical coastal lagoons of Northwest Mexico: Urias estuary (highly polluted) and Teacapan estuary (slightly polluted). Metazoan parasites were examined in 292 white mullet (Mugil curema) specimens collected bimonthly during a year from both systems. Haliotrema mugilinus, Metamicrocotyla macracantha, Ergasilus sp., Caligus sp., Holobomolochus sp., and Lernaeopodidae were found in gills, while Contracaecum sp. larvae III was found liver, hepatic portal vein and kidneys. Ecological indices were influenced by the slightly higher number of parasitic species in Urias compared to Teacapan, as well as the clear dominance of two species: Ergasilus sp. and Contracaecum sp. in both systems. In fact, Ergasilus sp. showed considerably higher abundance in Urias, possibly indicating that its success was a result of adverse conditions affecting the host, while Contracaecum sp showed higher abundances in Teacapan, suggesting that the environmental conditions occurring in Urias could have produced negative impacts on the nematode's infective potential.

Biomarkers have been useful tools to monitor some effects of pollution in coastal environments. Hepatic expression of heat-shock protein 70 (Hsp70) and cytochrome P450 1A (CYP1A) were analyzed in white mullet (Mugil curema) by RT-PCR from July, 2005 until July, 2006 in three coastal lagoons located in the southern Gulf of California, Mexico. These three coastal systems receive contaminants derived from local anthropogenic activities. Heat-shock proteins function to maintain protein integrity in the presence of stressors (such as heat or chemicals) and can be used as biomarkers of homeostatic alterations in polluted environments, whereas cytochrome P450 family members participate in steroid hormone synthesis and metabolism, and in xenobiotic transformation as a detoxification mechanism. The expression levels of both genes showed consistency in time and space, and presented a high overall correlation (r = 0.731, P < 0.001). Regardless of a high individual variability, both genes presented higher expression levels in the Urias Estuary (P < 0.001 and P < 0.05 for CYP1A and Hsp70, respectively), which was considered the most polluted among the three systems, especially during the rainy season (summer to fall). Gene expression levels were significantly associated with non-halogenated hydrocarbon concentrations in sediments during the sampling period (r = 0.686, P = 0.019 for CYP1A and r = 0.91, P < 0.001 for Hsp70), suggesting that both genes respond to chemicals in the environment. The results indicate that Mugil curema is a good candidate species to implement biomonitoring programs in tropical coastal environments.