Host-parasite interactions and the immunobiology of cestodes

Transforming gastrointestinal helminth parasite identification in vertebrate hosts with metabarcoding: a systematic review

BACKGROUND

Gastrointestinal helminths are a very widespread group of intestinal parasites that can cause major health issues in their hosts, including severe illness or death. Traditional methods of helminth parasite identification using microscopy are time-consuming and poor in terms of taxonomic resolution, and require skilled observers. DNA metabarcoding has emerged as a powerful alternative for assessing community composition in a variety of sample types over the last few decades. While metabarcoding approaches have been reviewed for use in other research areas, the use of metabarcoding for parasites has only recently become widespread. As such, there is a need to synthesize parasite metabarcoding methodology and highlight the considerations to be taken into account when developing a protocol.

METHODS

We reviewed published literature that utilized DNA metabarcoding to identify gastrointestinal helminth parasites in vertebrate hosts. We extracted information from 62 peer-reviewed papers published between 2014 and 2023 and created a stepwise guide to the metabarcoding process.

RESULTS

We found that studies in our review varied in technique and methodology, such as the sample type utilized, genetic marker regions targeted and bioinformatic databases used. The main limitations of metabarcoding are that parasite abundance data may not be reliably attained from sequence read numbers, metabarcoding data may not be representative of the species present in the host and the cost and bioinformatic expertise required to utilize this method may be prohibitive to some groups.

CONCLUSIONS

Overall, using metabarcoding to assess gastrointestinal parasite communities is preferable to traditional methods, yielding higher taxonomic resolution, higher throughput and increased versatility due to its utility in any geographical location, with a variety of sample types, and with virtually any vertebrate host species. Additionally, metabarcoding has the potential for exciting new discoveries regarding host and parasite evolution.

Imaging of neurocysticercosis and the influence of the human immunodeficiency virus

AIM

To review the literature on the imaging appearances of neurocysticercosis (NCC) and human immunodeficiency virus (HIV) co-infection and compare it with the local cases.

MATERIALS AND METHODS

Data from both published and local cases were analysed. HIV-infected cases were divided into "low" (<200 cells/mm³) and "high" (≥200 cells/mm³) CD4 groups. These groups were compared and the effect of treatment was evaluated.

RESULTS

Thirty-three cases were evaluated: 20 of the local cases and 13 published cases. The published cases had parenchymal brain cysts, whereas the local cases had both parenchymal and subarachnoid cysts (p=0.0050). The published cases also had intra-axial cysts, whereas the local cases had both intra- and extra-axial cysts (p=0.012). The published cases had predominantly cystic lesions, whereas the local cases had both cystic and granulomatous lesions (p=0.019). There were no differences between cases with a CD4 count of <200 cells/mm³ and cases with a CD4 count of ≥200 cells/mm³, but interestingly, 3% of the cases with a CD4 count of <500 cells/mm³, compared with 50% of the cases with a CD4 count of ≥500 cells/mm³, had racemose cysts.

CONCLUSION

NCC is very prevalent in South Africa and may complicate the diagnosis and treatment of patients with concomitant HIV infection. Patients with a "low" CD4 count may present with atypical lesions, delaying the diagnosis of NCC. Early initiation of highly active anti-retroviral therapy (HAART) may result in patients presenting with more classical symptoms and imaging appearances, thus improving outcomes.