In some areas of Argentina endemic for human T-lymphotropic virus type 1 (HTLV-1), tropical spastic paraparesis is frequent in subjects who lack antibodies against the virus; however, the relevance of this seronegative status in the country has not been investigated. In neighboring countries, HTLV-1 seronegative status has been described in patients with different diseases; however, data regarding features of seronegative HTLV-1 carriers are scarce. We investigated the seronegative status in 124 relatives of 28 HTLV-1 infected subjects from an endemic area in Northwest Argentina. Blood samples and clinical/epidemiological data were collected. Human T-lymphotropic virus type 1 infection was diagnosed by serology and long terminal repeat (LTR) sequence, env and tax gene detection. IgG anti-Tax HTLV-1 antibody, tax gene sequence, and DNA proviral load were also evaluated. Seventy-five percent of the 124 relatives were negative for HTLV-1/2 antibodies; 35.5% were also negative by molecular assays and 64.5% were negative for HTLV-1 LTR and env sequences, but positive for two sequences of HTLV-1 tax gene. Also, 35.7% of these subjects had IgG anti-Tax antibodies. The seronegative HTLV-1 status was significantly associated with male gender, youth, and sensory symptoms/autonomic nervous system dysfunction. High rates of seronegative symptomatic and asymptomatic HTLV-1 carriers in Argentina are described. The evidence highlights that HTLV-1 prevalence may be underestimated worldwide. Larger cohort studies are required to assess disease outcome in these seronegative subjects. Also, the findings emphasize the limitations of ongoing screening assays for diagnosis and blood safety. Therefore, algorithms for HTLV-1 diagnosis should include not only serological but also molecular assays.

Argentina's agricultural frontiers have been expanding causing a fragmentation and simplification of ecosystems and, therefore, a decline of biodiversity, and conditions that affect amphibian populations. Morphometry is used as a support to explain biological processes and in anurans it allows to relate morphometric variations relation to different environmental contaminants. The objective of this study is to provide basic data about external morphometry and corporal conditions of adult individuals from both sexes of Physalaemus biligonigerus (Cope, 1861) that inhabit a highly disturbed environment. It's important to point out that amphibians' changes in size and corporal conditions has been proposed as a reference to estimate environmental deterioration. The specimens analyzed were in two different environments with different antropic perturbation (agroecosystem and forest). Their corporal mass was registered (MC) as well as nine morphometric variables: snout to vent lenght (LHC), mouth width (AB), eye width (DO), inter-orbital distance (DIO), eye-nose distance (DON), forearm length (LAB), femur length (LF), tibia length (LT) and hindlimb toe length (LP). A corporal condition factor has been estimated 3 throught the ecuation K=[MC/LHC ]*100.000 to evaluate the general condition of the individuals. Compared to individuals coming from the forest the agroecosystem's specimens showed significant lower values in seven morphometric variables in females (LHC, DIO, DON, LB, LF, LT y LP) and five in males (LHC, DIO, DON, LT y LP). Also, it was observed that in both sexes the corporal condition factor was lower in the individuals coming from the agroecosystem. It concludes that the differences found between the analyzed populations might be related to the level of antropic perturbation.