Excretion/defecation patterns in Triatoma infestans populations that are, respectively, susceptible and resistant to deltamethrin

Pyrethroid resistance has been detected in Triatoma infestans (Klug) (Hemiptera: Reduviidae) specimens from different areas of Argentina and Bolivia. Genes conferring resistance can have a pleiotropic effect with epidemiological and evolutionary consequences. This research studied excretion/defecation patterns in deltamethrin-resistant T. infestans in order to elucidate its biological performance, adaptive consequences and role in the transmission of Chagas' disease. One deltamethrin-susceptible strain and two deltamethrin-resistant strains were used. Fifth-instar nymphs were fed ad libitum and their defecations recorded during and after the first or second feeding in the stadium. Resistant insects began to defecate later, defecated less, showed a lower proportion of defecating individuals and lower defecation indices compared with susceptible insects during the first hour after feeding. The number of bloodmeals in the stadium did not affect the main variables determining the pattern of defecation. The present study suggests that alterations in the excretion/defecation pattern in resistant insects entail an adaptive cost and, considering only this pattern, determine a lower capacity for transmission of Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) compared with susceptible insects.

The impact of antidepressant discontinuation versus antidepressant continuation on 1-year risk for relapse of bipolar depression: a retrospective chart review

BACKGROUND

Current treatment guidelines recommend discontinuation of an antidepressant within 3 to 6 months after remission of depression in patients with bipolar illness. Yet few studies directly compare the impact of antidepressant discontinuation versus antidepressant continuation on the risk for depressive relapse in patients with bipolar disorder who have been successfully treated for a depressive episode.

METHOD

In a retrospective chart review, patients with DSM-IV bipolar disorder who were treated for an index episode of depression by adding antidepressant medication to ongoing mood stabilizer medications were identified. The risk of depressive relapse in 25 subjects who stopped antidepressant medications after improvement was compared with the risk of depressive relapse in 19 subjects who continued antidepressants after improvement.

RESULTS

Termination of antidepressant medication significantly increased the risk of a depressive relapse. Antidepressant continuation was not significantly associated with an increased risk of mania.

CONCLUSION

While this study may have been limited by the retrospective nature of the chart review, nonrandomized assignment of treatment, and reliance on unstructured progress notes, it suggests that antidepressant discontinuation may increase the risk of depressive relapse in some patients with bipolar disorder. Further research is needed to clarify whether maintenance antidepressant treatment may be warranted in some patients with bipolar disorder, especially in those with frequent recurrent depressive episodes.