The epidemiology and detectability of asymptomatic plasmodium vivax and plasmodium falciparum infections in low, moderate and high transmission settings in Ethiopia

BACKGROUND

As countries move to malaria elimination, detecting and targeting asymptomatic malaria infections might be needed. Here, the epidemiology and detectability of asymptomatic Plasmodium falciparum and Plasmodium vivax infections were investigated in different transmission settings in Ethiopia.

METHOD

A total of 1093 dried blood spot (DBS) samples were collected from afebrile and apparently healthy individuals across ten study sites in Ethiopia from 2016 to 2020. Of these, 862 were from community and 231 from school based cross-sectional surveys. Malaria infection status was determined by microscopy or rapid diagnostics tests (RDT) and 18S rRNA-based nested PCR (nPCR). The annual parasite index (API) was used to classify endemicity as low (API > 0 and < 5), moderate (API ≥ 5 and < 100) and high transmission (API ≥ 100) and detectability of infections was assessed in these settings.

RESULTS

In community surveys, the overall prevalence of asymptomatic Plasmodium infections by microscopy/RDT, nPCR and all methods combined was 12.2% (105/860), 21.6% (183/846) and 24.1% (208/862), respectively. The proportion of nPCR positive infections that was detectable by microscopy/RDT was 48.7% (73/150) for P. falciparum and 4.6% (2/44) for P. vivax. Compared to low transmission settings, the likelihood of detecting infections by microscopy/RDT was increased in moderate (Adjusted odds ratio [AOR]: 3.4; 95% confidence interval [95% CI] 1.6-7.2, P = 0.002) and high endemic settings (AOR = 5.1; 95% CI 2.6-9.9, P < 0.001). After adjustment for site and correlation between observations from the same survey, the likelihood of detecting asymptomatic infections by microscopy/RDT (AOR per year increase = 0.95, 95% CI 0.9-1.0, P = 0.013) declined with age.

CONCLUSIONS

Conventional diagnostics missed nearly half of the asymptomatic Plasmodium reservoir detected by nPCR. The detectability of infections was particularly low in older age groups and low transmission settings. These findings highlight the need for sensitive diagnostic tools to detect the entire parasite reservoir and potential infection transmitters.

Adaptive Immunity in Hypertension

PURPOSE OF REVIEW

In recent years, a vast body of evidence has accumulated indicating the role of the immune system in the regulation of blood pressure and modulation of hypertensive pathology. Numerous cells of the immune system, both innate and adaptive immunity, have been indicated to play an important role in the development and maintenance of hypertension. The purpose of this review was to summarize the role of adaptive immunity in experimental models of hypertension (genetic, salt-sensitive, and Angiotensin (Ang) II induced) and in human studies. In particular, the role of T and B cells is discussed.

RECENT FINDINGS

In response to hypertensive stimuli such as Ang II and high salt, T cells become pro-inflammatory and they infiltrate the brain, blood vessel adventitia and periadventitial fat, heart, and the kidney. Pro-inflammatory T cell-derived cytokines such as IFN-γ and TNF-α (from CD8+ and CD4+Th1) and IL-17A (from the γδ-T cell and CD4+Th17) exacerbate hypertensive responses mediating both endothelial dysfunction and cardiac, renal, and neurodegenerative injury. The modulation of adaptive immune activation in hypertension has been attributed to target organ oxidative stress that leads to the generation of neoantigens, including isolevuglandin-modified proteins. The role of adaptive immunity is sex-specific with much more pronounced mechanisms in males than that in females. Hypertension is also associated with B cell activation and production of autoantibodies (anti-Hsp70, anti-Hsp65, anti-Hsp60, anti-AT1R, anti-α1AR, and anti-β1AR). The hypertensive responses can be inhibited by T regulatory lymphocytes (Tregs) and their anti-inflammatory IL-10. Adaptive immunity and its interface with innate mechanisms may represent valuable targets in the modulation of blood pressure, as well as hypertension-related residual risk.