The evolution of pyrimethamine resistant dhfr in Plasmodium falciparum of south-eastern Tanzania: comparing selection under SP alone vs SP+artesunate combination

BACKGROUND\ud \ud Sulphadoxine-pyrimethamine (SP) resistance is now widespread throughout east and southern Africa and artemisinin compounds in combination with synthetic drugs (ACT) are recommended as replacement treatments by the World Health Organization (WHO). As well as high cure rates, ACT has been shown to slow the development of resistance to the partner drug in areas of low to moderate transmission. This study looked for evidence of protection of the partner drug in a high transmission African context. The evaluation was part of large combination therapy pilot implementation programme in Tanzania, the Interdisciplinary Monitoring Programme for Antimalarial Combination Therapy (IMPACT-TZ) METHODS: The growth of resistant dhfr in a parasite population where SP Monotherapy was the first-line treatment was measured for four years (2002-2006), and compared with the development of resistant dhfr in a neighbouring population where SP + artesunate (SP+AS) was used as the first-line treatment during the same interval. The effect of the differing treatment regimes on the emergence of resistance was addressed in three ways. First, by looking at the rate of increase in frequency of pre-existing mutant dhfr alleles under monotherapy and combination therapy. Second, by examining whether de-novo mutant alleles emerged under either treatment. Finally, by measuring diversity at three dhfr flanking microsatellite loci upstream of the dhfr gene.\ud \ud RESULTS\ud \ud The reduction in SP selection pressure resulting from the adoption of ACT slowed the rate of increase in the frequency of the triple mutant resistant dhfr allele. Comparing between the two populations, the higher levels of genetic diversity in sequence flanking the dhfr triple mutant allele in the population where the ACT regimen had been used indicates the reduction in SP selection pressure arising from combination therapy.\ud \ud CONCLUSION\ud \ud The study demonstrated that, alleles containing two mutations at the dhfr have arisen at least four times independently while those containing triple mutant dhfr arose only once, and were found carrying a single unique Asian-type flanking sequence, which apparently drives the spread of pyrimethamine resistance associated dhfr alleles in east Africa. SP+AS is not recommended for use in areas where SP cure rates are less than 80% but this study reports an observed principle of combination protection from an area where pyrimethamine resistance was already high

Functional Hierarchy of Herpes Simplex Virus Type-1 Membrane Proteins in Corneal Infection and Virus Transmission to Ganglionic Neurons

© 2014 Informa Healthcare USA, Inc. All rights reserved. Purpose: To determine the relative importance of viral glycoproteins gK, gM, gE and the membrane protein UL11 in infection of mouse corneas and ganglionic neurons. Methods: Mouse eyes were scarified and infected with herpes simplex virus (HSV)-1(F), gE-null, gM-null, gK-null, or UL11-null viruses. Clinical signs of ocular disease were monitored daily. Virus shedding was determined at 24, 48 and 72h post infection. Viral DNA within trigeminal ganglia (TG) was quantified by quantitative PCR at 30d post infection. Results: The gE-null virus replicated as efficiently as the parental virus and formed viral plaques approximately half-the-size in comparison with the HSV-1(F) wild-type virus. The UL11-null and gM-null viruses replicated approximately one log less efficiently than the wild-type virus, and formed plaques that were on average one-third the size and one-half the size of the wild-type virus, respectively. The gK-null virus replicated more than 3-logs less efficiently than the wild-type virus and formed very small plaques (5-10 cells). Mice infected with the wild-type virus exhibited mild clinical ocular symptoms, while mice infected with the mutant viruses did not show any significant ocular changes. The wild-type virus produced the highest virus shedding post infection followed by the gM-null, gE-null and UL11-null viruses, while no gK-null virus was detected at any time point. All TG collected from mice infected with the wild-type virus and 6-of-10 of TG retrieved from mice infected with the UL11-null virus contained high numbers of viral genomes. The gE-null and gM-null-infected ganglia contained moderate-to-low number of viral genomes in 4-of-10 and 2-of-10 mice, respectively. No viral genomes were detected in ganglionic tissues obtained from gK-null eye infections. Conclusions: The results show that gK plays the most important role among gM, gE and UL11 in corneal and ganglionic infection in the mouse eye model