Evaluation of an epitope-blocking enzyme-linked immunosorbent assay for the diagnosis of West Nile virus infections in humans.

An epitope-blocking enzyme-linked immunosorbent assay (b-ELISA) was evaluated for the diagnosis of West Nile virus (WNV) infections in humans. Sera from patients diagnosed with WNV infections from an outbreak in 2003 in Colorado and from patients diagnosed with dengue virus infections from Mexico and Thailand were tested with the b-ELISA. The b-ELISAs were performed using the WNV-specific monoclonal antibody (MAb) 3.1112G and the flavivirus-specific MAb 6B6C-1. Although the WNV-specific b-ELISA was effective in diagnosing WNV infections in humans from Colorado, it was not efficacious for diagnosing WNV infections in serum specimens from Mexico and Thailand. In serum specimens from patients from Colorado, the WNV b-ELISA and the WNV plaque reduction neutralization test showed an overall agreement of 91%. The sensitivity and specificity of the WNV b-ELISA were 89% and 92%, respectively, with a false-positive rate of 5%, based on receiver operating characteristic analysis. In contrast, false-positive rate results in specimens from the countries of Mexico and Thailand, where flaviviruses are endemic, were 79% and 80%, presumably due to the presence of antibodies resulting from previous dengue virus infections in Mexico and/or Japanese encephalitis virus infections or vaccination in Thailand. Thus, in regions where people have experienced previous or multiple flavivirus infections, the use of the b-ELISA for WNV diagnosis is contraindicated.

Hepatitis B virus DNA in blood donors with anti-HBc as a possible indicator of active hepatitis B virus infection in Yucatan, Mexico.

Hepatitis B virus (HBV) may be present in serum even when negative for HBV surface antigen (HBsAg). If routine screening of sera for anti-HBV core antigen (anti-HBc) is not done, low-level HBV viraemia may not be identified. A study was done on the presence of HBV DNA in serum samples from Mexican blood donors negative for HBsAg. Sera from 158 volunteer blood donors, negative for HBsAg and anti-HBs, but positive for anti-HBc, were analysed using nested polymerase chain reaction (PCR). HBV DNA was detected in sera from 13 (8.23%) of the 158. Specificity of the PCR-amplified products was corroborated using Southern blot. Single strand conformation polymorphism (SSCP) analysis showed identical SSCP-banding patterns for all 13 PCR products, suggesting similar cDNA sequences. Occult HBV infection was observed in approximately 8% of anti-HBc only donors. The absence of HBsAg in the blood of apparently healthy individuals may not be sufficient to ensure lack of circulating HBV, and blood containing anti-HBc only may be infectious until proven otherwise.

[A case of autoimmune thrombocytopenic purpura and dengue]. / Caso de púrpura trombocitopénica autoinmune y dengue.

Dengue fever was detected in Yucatan in 1979. Since then, about 17,000 clinical cases have been reported, of which 1169 were confirmed by the presence of specific antibodies (IgM and IgG) and/or virologic studies; 10 of the cases were classified as dengue haemorrhagic fever and four died. The disease is endemic in the region and serotypes 1, 2 and 4 have been observed. This paper describes a patient with chronic autoimmune thrombocytopenic purpura who developed a primary dengue infection with hemorrhagic manifestations and responded to corticosteroids. We discuss the physiopathogeny of thrombocytopenia and analyze the utility of treatment with corticosteroids in patients with autoimmune disease.

Epidemic dengue 4 in the Yucatán, México, 1984.

An outbreak of dengue 4 occurred in the Yucatán, México in 1984. During the course of the outbreak, 538 of 5486 reported cases of dengue-like illness were studied; 200 were confirmed as dengue serologically and/or virologically. Dengue 4 virus was isolated from 34 patients and dengue 1 from one. Severe haemorrhagic symptoms were observed in 9 laboratory confirmed patients, including four deaths. Thus, the outbreak in Yucatán is the second dengue epidemic in the Americas after the Cuban epidemic in 1981 in which a number of patients suffered from haemorrhagic complications. It was notable that 5 of 9 hospitalized, severe cases were young adults and that only one met the WHO criteria of DHF, in contrast to primary pediatric nature of DHF in Southeast Asia. In this paper we describe clinical, serologic, and virologic studies conducted during the outbreak.

[The incidence of dengue virus infection in children 8 to 14 years old residing in the urban and rural areas of the city of Mérida, Yucatán]. / Incidencia de infección por virus dengue en niños de 8 a 14 años de edad radicados en las áreas urbana y rural del municipio de Mérida, Yucatán.

A prospective type study was conducted with two school cohorts from the urban and rural municipal area of Mérida, with the purpose of finding the incidence of infection due to the dengue virus, in a 4 month period when transmission was expected to be the highest. The serologic tests of the paired samples were done using the inhibition hemagglutination technique (IHA). We found the incidence of dengue virus infections in the city of Mérida was 4.56%, while that for the rural area was 5.67%. The prevalence of serological reactive against the same virus during the second sampling was 56.84% for the urban area and 63.70% for the rural area. No significant statistical different were found among the urban and rural incidences nor among the prevalences. The average hematocrit value found in school children from the urban area was 41.7 mL/dL and 40.4 mL/dL in the rural area. When comparing the median results of the hematocrit values, were found that there was significant statistical differences.

[Allergological study of pollen of mango (Magnifera indica) and cross reactivity with pollen of piru (Schinus molle)]. / Estudio alergológico del pólen del mango (Magnifera indica) y reactividad cruzada con el pólen del pirú (Schinus molle).

With immediate skin test, we studied hypersensitivity to pollen of mango (Magnifera indica), and its probability cross-sensitivity to pollen of pirú (Schinus molle), from anacardaceae class. We have made one extract of Magnifera indica, with 0.485 mg per 100, of protein nitrogen. With this extract we carry out skin test on non-atopic subjects and atopic subjects with bronchial asthma and or allergy rhinitis and common stock of aerealergen. (Freeman stock). We studied seventy-one subjects, both sexes, from 14 to 40 years old. The prevalence of cutaneous sensitive to mango (Magnifera indica) were 66%, and sensitivity from Schinus molle were 31%. Those with sensitivity Schinus molle, were sensitivity from Magnifera, too. Statistical analyisis of correlation, with McNemar Test was p 0.001 under the conditions of the study we conclude that there are hypersensitivity to pollen of Magnifera, and there are cross-reactivity with Schinus molle. Therefore mangifera should be included within the stock of skin test in the areas were this anacardaceae is present.