[The diagnosis of dengue in Mexico: an update and outlook]. / El diagnóstico del dengue en México: actualidad y perspectivas.

Few diseases have unique clinical findings sufficient to identify them. Dengue fever is not one of them, being necessary the clinical and laboratory support to confirm its diagnosis. Since dengue virus was first isolated, there has been a worldwide effort to develop cheaper and more accurate serologic diagnostic tests. Dengue hemorrhagic fever deserves closer attention because of its devastating clinical effects and lethal outcomes. In addition to the wide circulation of serotypes 1, 2 and 4 for over a decade in the Americas, the presence of Den-3 was detected again in 1994 since its last appearance in 1963 and 1977. Given the high rates of vectorial infestation and the presence of a susceptible population, the probability of circulation of this serotype in our continent is high. The present work defines the wide range of diagnostic methods available today, their advantages and disadvantages, and their importance in the epidemiological surveillance of dengue fever in Mexico.

[Immune response to poliovirus]. / Respuesta inmune a poliovirus.

General aspects on the immune response to poliovirus are described, considering it's molecular structure. Since the poliovirus is a cytocide agent, antibody immune response is the most important among those related to protection; however probably a minimum of helper T cells are required (more than 200 T lymphocytes with phenotype CD4) in order to get a best response. Phagocyte, NK cells and T lymphocytes probably take part in the viral clearance from the central nervous system, also in the host injure mechanisms. Some molecular aspects of the neutralizing antibodies combining site are described too. Activation particularities, of the common mucosal immune system confirm the importance of the secretory immune response in the control of the poliomyelitis.

Determinants and predictors of dengue infection in Mexico.

A national serosurvey was conducted in Mexico from March to October 1986 to identify predictors of dengue transmission and target areas at high risk of severe annual epidemics. A total of 3,408 households in 70 localities with populations less than 50,000 were randomly sampled, and serology was obtained from one subject under age 25 years in each household. When comparing exposure and infection frequencies across the 70 communities, the authors found that median temperature during the rainy season was the strongest predictor of dengue infection, with an adjusted fourfold risk in the comparison of 30 degrees C with 17 degrees C. High temperatures increase vector efficiency by reducing the period of viral replication in mosquitoes. The proportion of houses in a community with larva on the premises was significantly associated with the community proportion infected (odds ratio (OR)adj = 1.9; 95% confidence interval (CI) 1.4-2.5), as was the proportion of households with uncovered water containers present (ORadj = 1.9; 95% CI 1.4-2.7). Because these factors have effects beyond the individual household and subjects infected from them create a risk for other subjects, both analyses of effects and organization of control efforts must be at the community level. A predictive model was constructed using the community level risk factors to classify communities as being at high, medium, or low risk of experiencing an epidemic; 57% of these communities were correctly classified using this model.

[Immuno-epidemiologic considerations on the prevention of measles in Mexico]. / Consideraciones inmuno-epidemiológicas en la prevención del sarampión en México.

Study results of passive natural immunity anti-measles, and immune response to measles vaccine from different strains in Mexican children under one year old, are described in this paper. Mexican infants in these studies ended their maternal immunity at 8-10 months of age. Edmonston-Zagreb (EZ) vaccine strain had higher seroconversion rates comparing to Schwarz strain. Dose response effect was more closely related to Schwarz strain than EZ, since difference in seroconversion rates with standard, medium and high doses were statistically significant. However geometric mean post-vaccination titers were higher in children vaccinated with Schwarz strain, than EZ receptors.

[Seroconversion with trivalent Sabin vaccine in children less than four years of age]. / Seroconversión a la vacuna Sabin trivalente en niños menores de cuatro años de edad.

A group of 58 children under 4 years old, were vaccinated with trivalent oral poliovirus vaccine Sabin (OPV), in two sanitary areas of Chiapas, Mexico. The complement of procedures for the maintenance of the cold chain, and the changes in the potency of the vaccine prior and after the vaccination were evaluated. Nurses got a blood sample of 3cc and other one, four weeks after vaccination in order to evaluate the seroconversion rate attributable to Sabin vaccine, which was analyzed through neutralization serologic test. Moreover the investigation team got a sample of feces one day prior to vaccination and other one every week in the following three weeks to vaccination date in order to isolate the poliovirus in the feces of the children. The high pre-vaccination seropositivity suggests that in these areas exist a wide circulation of poliovirus, which probably were vaccine viruses and in less proportion wild viruses. The seroconversion rates were low for the three types of poliovirus, nevertheless 83% of the children had at least one of the three possibilities of seroconversion: unique, double or triple. Children with pre-vaccine seropositive probably had a secondary immune response.

[Saint Louis encephalomyelitis in Hermosillo, Sonora, Mexico. Its epidemiology]. / Encefalomielitis de San Luis en Hermosillo, Sonora, México. Su epidemiología.

In a warm desertic and irrigated region, with population 250 000 Northwest of Mexico, in Hermosillo, Sonora, along 8 weeks, 51 patients showed the following clinical data: fever, vomiting, neck rigidity, drowsiness and increase of cells and proteins in the CSF. In 12 patients good correlations were found between positive serologic results using SLE antigen by means of HI, CF and NT. Four paired sera showed fourfold increases in titers to SLE by means of HI or CF. With VEE antigen no such increases were found. The cases were scattered geographically, most of them occurred within an urban area, and affected people in 13 localities. The outbreak developed from August to September, 1974, the attack rate was 22/100 000, 69% of the patients being children under 15 years of age. The case fatality rate was 20%. A prosperous chicken industry existed in the region and epizootics were not reported in either domestic or wild animals at that time.

St. Louis encephalomyelitis in Hermosillo, Sonora, Mexico.

This report, which describes an epidemic of St. Louis encephalitis in northwestern Mexico, was prompted by the apparent infrequency of previous Mexican outbreaks of this disease. The site of the epidemic was the Municipality of Hermosillo in the State of Sonora. This municipality, with a population of about 273,000, is situated in a hot flat area which is naturally dry but which is also well-irrigated. Here, over an eithy-week period, 51 persons became ill and were hospitalized with symptoms including fever, vomiting, stiff neck, lethargy, and increased cell/protein levels in their cerebrospinal fluid. Sera from 12 of these patients were tested for SLE antibodies by hemagglutination inhibition, complement fixation, and neutralization. The results of these tests were positive and showed a fairly high degree of correlation. In addition, paired serum samples showed a significant rise in SLE antibody titers. Over half of the cases occurred in the City of Hermosillo, the municipal seat; the remainder occurred in 13 outlying areas, most of them quite nearby. Virtually all of the city dwellers affected were residents of low-income districts. The rate of hospital cases was roughly 19 per 100,000 inhabitants, and the case-fatality rate among these cases was approximately 20 per cent. The ratio of male to female patients was 1.3 to 1; sixty-nine per cent of the patients were under 16 years of age.