[Dengue, zika, chikungunya and the development of vaccines]. / Dengue, zika, chikungunya y el desarrollo de vacunas.

Dengue (DENV), zika (ZIKV) and chikungunya (CHIKV), three arbovirosis transmitted by Aedes mosquitoes, have spread in recent decades in humid tropical and subtropical zones. Dengue is epidemic in subtropical areas of Argentina. DENV infection confers lasting immunity against the infecting serotype but increases the risk of serious disease upon reinfection by any of the other three. The recombinant tetravalent vaccine Dengvaxia® prevents severe dengue and hospitalization in seropositive subjects. In 2017, Dengvaxia was approved in Argentina, for ages 9 to 45, but is not included in the national vaccination calendar. Two other vaccines are in Phase III evaluation: one developed by NIAID / Instituto Butantan and the other by Takeda. ZIKV, a virus associated with microcephaly in newborns in Brazil, circulates since 2016 in Argentina. There is still not effective treatment nor vaccine with proven activity against ZIKV. There has been no active circulation of CHIKV in Argentina in 2017. Outbreaks of CHIKV fever have a complication: the development of chronic post-disease rheumatism. There are not approved vaccines for humans nor effective antiviral therapies. The seriousness of these virosis has contributed to a rapid progress in the knowledge of the infection processes and the immune response. For now, Aedes aegypti and A. albopictus vectors continue to expand, suggesting that the vaccine will be the most effective means of controlling these viruses. Here we summarize information about these arbovirosis in Argentina and Brazil and describe advances in the development and evaluation of vaccines.

[One hundred years after the "Spanish" flu]. / A cien años de la gripe "española".

The "Spanish" flu pandemic, which occurred a century ago, is considered the most devastating in human history. An estimated one third of world population fell ill with flu and more than 2.5% of them died. The course of the epidemic had two main waves (1918 and 1919) and showed an unusual W-shaped morbidity/mortality distribution. Death was not a direct outcome of flu itself but rather a consequence of secondary bacterial bronchopneumonia, for which antibiotics had not yet been discovered. Pre-existing pulmonary tuberculosis was also accountable for increased flu death rates during the pandemic. As it happened in Europe, in Argentina the epidemic had two main waves, with ample variation in mortality by region. Available treatment at the time included diet, throat antiseptic rinses, low doses of quinine valerianate, salicylates, codeine as a cough suppressant, and camphor oil. Primitive anti-pneumococcal vaccines and immune sera were also applied. Upon the disclosure of the whole RNA sequence of the 1918 influenza virus genome, by means of reverse genetics it was possible to assemble viral particles resembling those of the deadly pandemic. The reconstituted virus proved to be extraordinarily virulent for mice. Current seasonal flu vaccines help to reduce, but not to abolish, the risk of another pandemic. The ongoing development of "universal" vaccines against influenza conferring reliable and long-lasting immunity may prevent its global spread in the future.

[Dengue, Zika and Chikungunya]. / Dengue, Zika y Chikungunya.

Arboviruses are transmitted by arthropods, including those responsible for the current pandemic: alphavirus (Chikungunya) and flaviviruses (dengue and Zika). Its importance increased in the Americas over the past 20 years. The main vectors are Aedes aegypti and A. albopictus. Dengue infection provides long lasting immunity against the specific serotype and temporary to the other three. Subsequent infection by another serotype determines more serious disease. There is a registered vaccine for dengue, Dengvaxia (Sanofi Pasteur). Other two (Butantan and Takeda) are in Phase III in 2016. Zika infection is usually asymptomatic or occurs with rash, conjunctivitis and not very high fever. There is no vaccine or specific treatment. It can be transmitted by parental, sexual and via blood transfusion. It has been associated with microcephaly. Chikungunya causes prolonged joint pain and persistent immune response. Two candidate vaccines are in Phase II. Dengue direct diagnosis is performed by virus isolation, RT-PCR and ELISA for NS1 antigen detection; indirect methods are ELISA-IgM (cross-reacting with other flavivirus), MAC-ELISA, and plaque neutralization. Zika is diagnosed by RT-PCR and virus isolation. Serological diagnosis cross-reacts with other flavivirus. For CHIKV culture, RT-PCR, MAC-ELISA and plaque neutralization are used. Against Aedes organophosphate larvicides (temephos), organophosphorus insecticides (malathion and fenitrothion) and pyrethroids (permethrin and deltamethrin) are usually employed. Resistance has been described to all these products. Vegetable derivatives are less expensive and biodegradable, including citronella oil, which microencapsulated can be preserved from evaporation.

[Tuberculosis 110 years after the Nobel Prize awarded to Koch]. / La tuberculosis a 110 años del Premio Nobel de Koch.

The Nobel Prize in Physiology or Medicine was awarded in 1905 to Robert Koch "for his investigations and discoveries in relation to tuberculosis (TB)". He discovered the causal agent of TB, described the four principles that since then have guided research in communicable diseases and also prepared the old tuberculin, a bacillary extract that failed as a healing element but allowed the early diagnosis of TB infection and promoted the understanding of cellular immunity. After his death, the most conspicuous achievements against TB were the BCG vaccine, and the discovery of streptomycin, the antibiotic that launched the era of the effective treatment of TB. Drug-resistance soon appeared. In Argentina, studies on drug resistance began in the 60s. In the 70s, shortened anti-TB drug schemes were introduced consisting in two-month treatment with four drugs, followed by four months with two drugs. The incidence of TB decreased worldwide, but the immune depression associated with awarded together with the misuse of anti-TB drugs allowed the emergence of multidrug resistance and extensive resistance, with the emergence of nosocomial outbreaks worldwide, including Argentina. New rapid diagnostic methods based on molecular biology were developed and also new drugs, but the treatment of multidrug resistant and extensively resistant TB is still difficult and expensive. TB research has marked several milestones in medical sciences, including the monumental Koch postulates, the tuberculin skin test that laid the basis for understanding cell-mediated immunity, the first design of randomized clinical trials and the use of combined multi-drug treatments.

[Syphilis in Argentina]. / Sífilis en Argentina.

Syphilis is a disease preventable through sexual protection barriers, and curable with a simple treatment. Despite this, between 2010 and 2019, its incidence almost tripled in Argentina, reaching 56.1/100 000. The most affected are young people (15-24 years old), with a higher percentage of women, especially among pregnant women, in whom it increased from 2.3% to 5.8%, with a peak of 7.7% between 15 and 24 years old. Cases of secondary or tertiary syphilis, detected by control tests, are on the rise. The increase in syphilis is linked to HIV. For this reason, rapid detection tests must be carried out jointly at the first level of care, which facilitates access to the diagnosis and treatment of positive cases, with the corresponding guidance and control. Treatment with penicillin, for which no resistance has been found, is the key component of control. Doxycillin is also used (not in pregnant women), or ceftriaxone. The resistance of Treponema pallidum to azithromycin is increasing, so its use should be avoided. In 2022, 696 cases of congenital syphilis were reported. The national rate is 1.3 per 1000 live births. The majority of reported cases come from the public sector. Maternal syphilis is, in low-income areas, the most common cause of stillbirths. Strict application of existing regulations, strengthening the primary care system, and prevention during pregnancy can contribute to controlling and eliminating the syphilis problem in Argentina.

La sífilis es una enfermedad prevenible mediante barreras de protección sexual, y curable por un sencillo tratamiento. A pesar de esto, entre 2010 y 2019, su incidencia casi se triplicó en Argentina, alcanzando 56.1/100 000. Los más afectados son los jóvenes (15-24 años), con mayor porcentaje de mujeres, especialmente entre las embarazadas, en que aumentó de 2.3% a 5.8%, con un pico de 7.7% entre 15 y 24 años. Los casos de sífilis secundaria o terciaria, detectados por pruebas de control, están en aumento. El aumento de sífilis va unido al HIV. Por ello las pruebas rápidas de detección deben hacerse conjuntamente en el primer nivel de atención, lo que facilita el acceso al diagnóstico y al tratamiento de los casos positivos, con la orientación y control correspondientes. El tratamiento con penicilina, para la que no se ha hallado resistencia, es el componente clave del control. También se usa doxicilina (no en embarazadas), o ceftriaxona. Está aumentando la resistencia del Treponema pallidum a la azitromicina, por lo que debe evitarse su empleo. En 2022 se notificaron 696 casos de sífilis congénita. La tasa de nacional es 1.3 por 1000 nacidos vivos. La mayoría de los casos notificados provienen del sector público. La sífilis materna es, en áreas de bajos recursos, la causa más común de nacidos muertos. La aplicación estricta de las normas existentes, el fortalecimiento del sistema de atención primaria, y la prevención durante el embarazo, pueden contribuir a controlar y eliminar el problema de la sífilis en Argentina.

[Zoonotic tuberculosis in Argentina]. / La tuberculosis zoonótica en la Argentina.

There are significant achievements in the control of animal tuberculosis (tB) in Argentina. the percentage of bovines with apparent tB lesions at the slaughterhouse inspection decreased from 6.7% to 0.6% between 1969 and 2011. on the other hand, the mean percentage of human tB cases due to M. bovis among all those bacteriologically confirmed, was in Santa Fe, an agro-industrial province, 2.3% in the period 1977-2001. It fell to 1.6% by 2011. In the Cetrángolo Hospital (Buenos Aires), it was 0.34% in the period 2001-2005, and 0.36% in 2006-2011. At the Muñiz Hospital, these percentages decreased from 1.75% in 1971 to 0.22% in 2006. Frequency of HIV infection among M. bovis cases varied from 5.9% in santa Fe to 11.1% and 20.5% respectively, in Cetrángolo and Muñiz Hospitals (a reference institution for aids) in Buenos Aires. According to these data M. bovis infection predominates in agro-industrial/ rural areas, showing a slow decrease there as well as in Buenos Aires. Co-infection with HIV is more frequent among patients with M. bovis that in all cases of tB. The situation of M. bovis in Argentina is here compared with that in USA and in several European and Latin American countries. Trends followed by tB in cattle, in humans, and the percentages of M. bovis among them, are not always closely related to move towards the common goal of eradicating tB; the employment of appropriate strategies and the strengthening of control measures are critical in both programs.

One hundred years of BCG vaccine.

The BCG vaccine was given for the first time in 1921, in Paris, to a newborn of a mother with tuberculosis. Between 1924 and 1960, the Pasteur Institute delivered BCG cultures to more than 50 laboratories around the world. In 1925, Dr Andrés Arena introduced the BCG seed to Argentina, where the vaccine began to be produced and applied orally to newborns. The original strain underwent diverse genetic changes in different parts of the world, which did not seem to affect its protective efficacy. In Argentina, a study (1978-1985) showed that BCG prevents primary TB in general, and has 100% efficacy in meningitis and other extra-pulmonary TB locations. BCG effect is independent of TB control measures (case detection and treatment). Furthermore, BCG provides nonspecific protection from various infections and is used in the treatment of bladder cancer. By 2020, at least five technologies had already been established for the future development of anti-TB vaccines: cellular vaccines, protein subunits, nucleic acids, with adenovirus vector, and with recombinant influenza virus as a vector. There are currently more than 20 TB vaccine candidates under evaluation. History teaches, and the COVID-19 pandemic has confirmed, that vaccination is a fundamental instrument for the control of infectious diseases. Until a more effective vaccine becomes available, BCG will continue to be included in the Argentine National Vaccination Calendar for application to newborns.

La vacuna BCG fue administrada por primera vez en 1921, en París, a un recién nacido de madre tuberculosa. Entre 1924 y 1960, el Instituto Pasteur entregó cultivos de BCG a más de 50 laboratorios de todo el mundo. En 1925, el Dr. Andrés Arena lo introdujo en Argentina, donde se comenzó a producir y aplicar la vacuna a recién nacidos por vía oral. La cepa original sufrió múltiples cambios genéticos que, sin embargo, no parecen haber afectado su eficacia protectora, establecida aun sin que se conociera el mecanismo de acción. En Argentina, un estudio (1978-1985) demostró que la BCG previene la TB primaria en general, y en un 100% la meningitis y otras localizaciones extrapulmonares. Su efecto es independiente de las medidas de control de la TB (detección de casos y tratamiento). Además, se la usa en el tratamiento del cáncer de vejiga y provee protección inespecífica contra diversas enfermedades infecciosas. En 2020 ya se habían establecido por lo menos 5 tecnologías para el futuro desarrollo de vacunas anti-TB: vacunas celulares, de subunidades proteicas, de ácidos nucleicos, con vector adenovirus, y con virus influenza recombinante como vector. Actualmente hay más de 20 vacunas candidatas anti-TB. La historia enseña, y la pandemia de COVID-19 ha contribuido a revalorizar, que la vacunación es un instrumento fundamental para el control y la erradicación de las enfermedades infecciosas. Y hasta que haya disponible otra más eficaz, BCG seguirá figurando en el Calendario de Vacunación Nacional, para ser aplicada al recién nacido.

SARS-CoV-2 variants and the so-called resistance to vaccines.

RNA viruses (except retroviruses) replicate by the action of an RNA-dependent RNA polymerase, which lacks a proofreading exonuclease and, consequently, errors may occur in each replication giving place to viral mutants. Depending on their fitness, these mutants either become extinct or thrive, spawning variants that escape the immune system. The most important SARS-CoV-2 mutations are those that alter the amino acid sequence in the viral S protein because this protein holds the key for the virus to enter the human cell. The more viruses replicate, the more they mutate, and the more likely it is that dominant resistant variants will appear. In such cases, more stringent measures for community protection will be required. Vaccines and polyclonal antibodies, which induce a response directed towards several sites along the S protein, would maintain effective protection against SARS-CoV-2 variants. Furthermore, vaccines appear to induce an increased helper and cytotoxic T-cell response, which may also be a biomarker of protection. In densely populated areas with insufficient protection measures, the virus spreads freely, thus increasing the likelihood of generating escape mutants. India and Manaus exemplify this situation. Natural evolution selects the mutants that multiply most efficiently without eliminating the host, thus facilitating their spread. Contrastingly, the circulation of viruses of high virulence and lethality (Ebola, hantavirus) that eliminate the host remain limited to certain geographic areas, without further dissemination. Therefore, it would be expected that SARS-CoV-2 will evolve into more infectious and less virulent variants.

Los virus ARN, excepto los retrovirus, se replican por acción de una ARN polimerasa ARN-dependiente que carece de exonucleasa correctora y, en consecuencia, en cada replicación puede cometer errores. Así se originan mutantes que, según su menor o mayor fitness, se extinguen o bien prosperan y originan variantes que escapan al sistema inmune. Las mutaciones de SARS-CoV-2 más importantes son las que alteran la proteína viral S, porque ella tiene la llave de ingreso del virus a la célula humana. Cuanto más se replican los virus, más mutan, y se hace más probable que aparezcan variantes resistentes dominantes. En esos casos, se requerirá una aplicación más estricta de las medidas de protección de la comunidad. Las vacunas y los anticuerpos policlonales, que inducen una respuesta dirigida hacia toda la proteína S, mantendrían protección efectiva contra las variantes del SARSCoV-2. Además, las vacunas inducirían una mayor respuesta de células T helper y citotóxicas, lo que puede ser un biomarcador de protección. En áreas densamente pobladas con escasas medidas de protección, el virus se difunde libremente y aumenta la probabilidad de mutaciones de escape. India y Manaos ejemplifican esa situación. La evolución natural selecciona las mutantes que se reproducen con mayor eficiencia sin eliminar al huésped, lo que facilita la propagación. En cambio, la circulación de virus de alta virulencia y letalidad (Ebola, hantavirus), que eliminan al huésped, se circunscribe a determinadas áreas geográficas, sin mayor difusión. Por lo tanto, sería esperable que SARS-CoV-2 evolucione a variantes más infecciosas y menos virulentas.

[The seventieth anniversary of Medicina (Buenos Aires)]. / Setenta aniversario de Medicina (Buenos Aires).

The historical trajectory of Medicina (Buenos Aires) and the current challenges accompanying its seventieth birthday are briefly described. The initial objectives at its foundation were to contribute to the advance of medicine, and support both clinical and experimental research in Argentina. These objectives continue to be valid. The editorial presence of the journal continues to be necessary. It is published following the international quality standards, the peer review system, and it is indexed in the main international data bases for scientific journals.

[Measles]. / Sarampión.

In April 2019, UNICEF denounced that more than 20 million children worldwide had not been vaccinated and alerted on possible outbreaks of measles which, due to the high transmissibility of this virus, is the first disease preventable by vaccination to emerge. If the decline in vaccinations continues, pertussis, tetanus and other diseases, which require less coverage to achieve population protection, may also reappear. In Argentina, the current outbreak began in late August 2019. Measles virus is transmitted by air, infects multiple organs, and is associated with immunosuppression. Its genome consists of single stranded RNA. Genotyping is carried out by sequencing a 450-nucleotide fragment of the N protein, which contains the highest density of nucleotide variation. In South America, D8 is the circulating genotype and in North America, B3 accounts for 8% of the cases. Each person with measles infects, on average, another 12-18 people in a susceptible population. Vaccination confers direct and indirect protection, and induces both antibodies and cellular immunity. Newborns are protected by maternal antibodies transmitted via the placenta, up to 6 months. In Argentina, the Vaccination Calendar includes two doses of triple viral vaccine, at 12 months and 5 years, and a zero dose (6-11 months of age) in districts with disease cases. The protection conferred by the vaccine is 93% at 12 months with a dose, and with 2 doses 97% for life.

En abril de 2019, UNICEF denunció que más de 20 millones de niños en todo el mundo no habían sido vacunados y alertó sobre posibles brotes de sarampión que, por su alta contagiosidad, es la primera enfermedad en emerger entre las prevenibles mediante vacunación. De continuar el descenso en las vacunaciones, podrían reaparecer también pertussis, tétanos y otras enfermedades con menor requerimiento de cobertura para alcanzar protección poblacional. A fin de agosto de 2019 se inició en la Argentina el actual brote de sarampión. Este virus se transmite por vía respiratoria, infecta múltiples órganos e induce inmunosupresión. Su genoma consiste en ARN de cadena simple. La genotipificación se efectúa por secuenciación de un fragmento de 450 nucleótidos de la proteína N que contiene la mayor densidad de variación de nucleótidos del genoma. En Sudamérica circula el genotipo D8, y en Norteamérica hay, además, un 8% de genotipo B3. Cada persona con sarampión infecta, en promedio, otras 12-18 en una población susceptible. La vacunación confiere protección directa e indirecta, e induce tanto anticuerpos como inmunidad celular. Los recién nacidos tienen protección hasta los 6 meses por anticuerpos maternos transmitidos vía placentaria. En la Argentina, el Calendario de Vacunación incluye dos dosis de triple viral, a los 12 meses y a los 5 años, y una dosis cero (6-11 meses de edad) en distritos con casos de enfermedad. Una dosis protege al 93% de los vacunados a los 12 meses y dos dosis al 97%, de por vida.

[Is the tuberculin skin test still suitable to diagnose tuberculosis infection ?]. / ¿Es suficiente la prueba tuberculínica para el diagnóstico de la infección tuberculosa ?

Tuberculosis (TB) infection is currently being diagnosed by the tuberculin skin test (TST) with PPD. Some Mycobacterium tuberculosis PPD components are present in BCG, which can be the cause of false positive TST results in BCG vaccinated persons. New IFN-g release assays (IGRAs) are based on the ex vivo release of IFN-g by peripheral blood cells in presence of M. tuberculosis antigens ESAT-6 and CFP-10, which should be absent in BCG. These assays consist in either quantifying released IFN-g or enumerating IFN-g producing cells. In principle, IGRAs should differentiate true TB infection from vaccination and results of several studies suggest that these assays display lower positivity than TST. Whether the lower positivity could be attributed to higher specificity or to lower sensitivity as compared with PPD is still unclear. BCG vaccination, if not recently applied, cannot be blamed for false positive TST reactions. Strong TST reactions (> or = 10 mm or > or =15 mm) are highly correlated with TB infection. In settings where TB continues being a serious health problem, cost-effectiveness evaluations would privilege TST under certain conditions: supply of quality-assured PPD reagent, standardized criteria for TST application, reading and interpretation, and regular availability in health centers countrywide. In view of current limitations in the supply of imported PPD in Argentina, its production/quality assurance should be considered a public health priority. Still, key questions remain to be addressed concerning the role of IGRAs and TST in predicting risk of TB disease, in other words, in identifying persons who will benefit most from chemoprophylaxis.

Human Mycobacterium bovis infection in ten Latin American countries.

The aim of this work was to obtain the best possible estimate of the relevance of bovine tuberculosis (BTB) in humans in Argentina, Brazil, Chile, Colombia, Costa Rica, Dominican Republic, Ecuador, Peru, Uruguay and Venezuela. Sources of information were a questionnaire filled by the participant laboratories, and a search of published literature (1970-2007). Only four of these countries reported bacteriologically confirmed cases of BTB in humans. Most of these were diagnosed in Argentina, where the mean percentage of Mycobacterium bovis cases in relation to those due to Mycobacterium tuberculosis (2000-2006) ranged from 0.34% to 1.0%, according to the region. A slowly decreasing trend was observed in non HIV as well as in HIV/AIDS patients in Buenos Aires. In most of these countries, the low coverage of culture methods, especially of those including pyruvate-containing media, appropriate to isolate M. bovis, contributes to an underestimate of the problem. It was confirmed that BTB in humans exists, even though its relevance seems to be low. Milk pasteurization, sanitary controls to dairy products, and meat inspection at slaughterhouses contribute to the protection of human health. However, occupational aerogenous exposure to TB cattle and their carcasses remains a source of infection in the region.

Sífilis en Argentina / Syphilis in Argentina

Resumen La sífilis es una enfermedad prevenible mediante barreras de protección sexual, y curable por un sen cillo tratamiento. A pesar de esto, entre 2010 y 2019, su incidencia casi se triplicó en Argentina, alcanzando 56.1/100 000. Los más afectados son los jóvenes (15-24 años), con mayor porcentaje de mujeres, especialmente entre las embarazadas, en que aumentó de 2.3% a 5.8%, con un pico de 7.7% entre 15 y 24 años. Los casos de sífilis secundaria o terciaria, detectados por pruebas de control, están en aumento. El aumento de sífilis va unido al HIV. Por ello las prue bas rápidas de detección deben hacerse conjuntamente en el primer nivel de atención, lo que facilita el acceso al diagnóstico y al tratamiento de los casos positivos, con la orientación y control correspondientes. El tratamiento con penicilina, para la que no se ha hallado resistencia, es el componente clave del control. También se usa doxicilina (no en embarazadas), o cef triaxona. Está aumentando la resistencia del Treponema pallidum a la azitromicina, por lo que debe evitarse su empleo. En 2022 se notificaron 696 casos de sífilis congénita. La tasa de nacional es 1.3 por 1000 nacidos vivos. La mayoría de los casos notificados provienen del sector público. La sífilis materna es, en áreas de bajos recursos, la causa más común de nacidos muertos. La aplicación estricta de las normas existentes, el fortalecimiento del sistema de atención primaria, y la prevención durante el embarazo, pueden contribuir a controlar y eliminar el problema de la sífilis en Argen tina.

Abstract Syphilis is a disease preventable through sexual pro tection barriers, and curable with a simple treatment. Despite this, between 2010 and 2019, its incidence al most tripled in Argentina, reaching 56.1/100 000. The most affected are young people (15-24 years old), with a higher percentage of women, especially among pregnant women, in whom it increased from 2.3% to 5.8%, with a peak of 7.7% between 15 and 24 years old. Cases of secondary or tertiary syphilis, detected by control tests, are on the rise. The increase in syphilis is linked to HIV. For this reason, rapid detection tests must be carried out jointly at the first level of care, which facilitates access to the diagnosis and treatment of positive cases, with the cor responding guidance and control. Treatment with penicillin, for which no resistance has been found, is the key component of control. Doxycillin is also used (not in pregnant women), or ceftriaxone. The resistance of Treponema pallidum to azithromycin is increasing, so its use should be avoided. In 2022, 696 cases of congenital syphilis were re ported. The national rate is 1.3 per 1000 live births. The majority of reported cases come from the public sector. Maternal syphilis is, in low-income areas, the most com mon cause of stillbirths. Strict application of existing regulations, strength ening the primary care system, and prevention during pregnancy can contribute to controlling and eliminating the syphilis problem in Argentina.

Susceptibility tests to second line drugs and re-treatment of tuberculosis revisiting early experiences.

The value of susceptibility tests in guiding antituberculous therapy with second-line drugs remains controversial. We reanalyzed three reports regarding the relationship between in vitro susceptibility of Mycobacterium tuberculosis and the clinical outcome of in-patients treated with these drugs at the Muñiz Hospital, Buenos Aires, during the sixties. These patients had been irregularly treated with a standard regimen consisting of isoniazid, streptomycin and PAS; they developed resistance to at least the first two drugs and persisted culture-positive. Susceptibility testing to ethionamide, cycloserine and kanamycin were performed by the proportion method on Löwenstein Jensen medium. Some level of resistance was detected among isolates from patients not previously treated with these drugs, that could be due to cross resistance with previously administered first line structural analogs. However, the studies evidenced significant association between resistance to ethionamide and cycloserine and prior treatment with these drugs. Increased resistance to all three drugs was detected within the first three months of treatment. In vitro resistance to ethionamide emerged earlier and was the most frequent followed by resistance to cycloserine and kanamycin. The low frequency of resistance to kanamycin could be related to the low dosage of this drug used at that time. Simultaneous resistance to the three agents, but not to two or one drug, appeared to be a marker of treatment failure. An apparent reversion of drug resistance was observed in near 6% of patients, for whom susceptibility tests were repeated on subsequent isolates, indicating this percentage of inconsistency in reproducibility of test results.