Correlation between cardiac and skeletal muscle alterations produced by the presence of T. cruzi in these tissues

LO PRESTI MS; RIVAROLA HW; MICUCCI L; BUSTAMANTE JM; FRETES R; TRIQUELL MF; PAGLINI-OLIVA PA

Río de Janeiro. Brasil

Simposio; International Symposium The Centenary of Chagas disease discovery; 2009

It has been demonstrated that in the human body, T. cruzi can parasitize any tissue; however, the intensity of the infection varies from case to case, depending on the host condition and parasite genetic background. Since smooth and striated muscles are usually heavily invaded, we studied cardiac and skeletal muscle samples from different infected models in order to see the alterations produced by the infection and if the parasites were located in these organs. Albino swiss mice were infected with either Tulahuen strain (Tul, n=100) or SGO-Z12 isolate (Z12, n=100) and studied through parasitemia, electrocardiography and histopathology along the acute (Ac, 30-50 days post infection –d.p.i.), chronic indeterminate (In, 75-90 d.p.i.), early cardiac chronic (E-Ch, 135 d.p.i.) and late cardiac chronic phases (L-Ch, 365 d.p.i) of the experimental infection. Thirty mice from each group were reinfected (Tul-R and Z12-R) on days 10 and 20 p.i. with the same parasite strain as the first infection and studied at the same time points as the previous groups. Non-infected mice (NI, n=30) were also studied. Parasitemia was determined weekly in a Neubauer haemocytometer. Electrocardiographic tracings (ECG) were obtained with a digital electrocardiographic unit under Ketamine ClH anaesthesia (10 mg/Kg). For the histopathology studies, mice were sacrificed by decapitation, previous Ketamine anesthesia. Hearts and skeletal muscle samples from the posterior legs of the mice from the different groups were removed, fixed in buffered 10% formaldehyde (pH 7.0), and embedded in paraffin. Each sample was cut into 5mm sections and stained with Hematoxilin-Eosine. Similar sections were stained with an anti-T. cruzi fluorescent antibody and studied by inmunofluorescence. Parasitemia was higher in Tul than in Z12 from day 7 to day 42 p.i. (p<0.01), when parasites in blood became undetectable in both groups. Z12-R and Tul-R presented circulating parasites until 63 and 70 d.p.i respectively. The ECG alterations increased with the evolution of the infection, being the atrio-ventricular and intra-ventricular blockades the most common findings in the acute and cardiac phases respectively. Tul-R and Z12-R showed higher percentage of mice with ECG alterations (60-100% in the cardiac phase). The cardiac histopathological alterations also accumulated with the evolution of the infection in both infected groups: Ac: mild inflammatory infiltrates; In: moderate inflammatory infiltrates and fiber fragmentation; E-Ch: disperse inflammatory infiltrates, fiber dissolution and necrosis; L-Ch: necrosis, fiber fragmentation and inflammatory infiltrates. In this last stage, Tul also presented thickening of the epicardium. Tul-R presented fiber disorganisation and fibrosis in the acute phase and necrosis (as well as the Z12-R) from the chronic indeterminate stage. The alterations in the skeletal muscle samples were similar to the cardiac ones, but more intense, with structural disorganization, necrosis and intense inflammatory infiltrates in Tul and Z12. Amastigote nests were frequent in both infected and reinfected groups in the skeletal muscle samples throughout the infection. Present results show that the alterations found in the skeletal muscle are similar to those found in the heart, but more intense and with the presence of parasite nests. This finding demonstrates the presence of the parasite in the cardiac chronic phase of the infection and show the skeletal muscle as a reservoir of parasites, even when no circulating forms are detected. The differences between the infected groups can be attributed to the genetic variation and heterogeneity between the parasite strains.