ABSTRACT
Starting in October 2021, quarterly malacological surveys have been undertaken in Malawi, with the sampling of 12 specified freshwater habitats throughout a calendar year. Each survey monitors the presence of aquatic intermediate snail hosts of medical and veterinary importance. In March 2023, the alien lymnaeid species Pseudosuccinea columella was encountered for the first time in the surveys, in Nsanje District. This species identity was later confirmed upon DNA analysis of mitochondrial ribosomal 16S sequences. In July 2023, P. columella was also noted at single sites within Mangochi and Chikwawa Districts, and again in Nsanje District, with an additional location observed. Of particular importance, our sampled location in Mangochi District was directly connected to Lake Malawi, which expands the species list of invasive molluscs in this lake. While P. columella is a well-known intermediate snail host for human and animal fascioliasis, screening collected snails for trematode cercariae, alongside molecular xenomonitoring, did not yield equivocal evidence of active fluke infection. However, the newly recognized presence of this alien intermediate snail host within Lake Malawi, and along the Shire River Valley, flags a new concern in altered local transmission potential for human and animal fascioliasis.
Subject(s)
Fasciola hepatica , Fascioliasis , Animals , Humans , Fasciola hepatica/genetics , Fascioliasis/veterinary , Malawi , SnailsABSTRACT
The freshwater amphibious snail Orientogalba viridis commonly occurs in eastern Asia, on certain Pacific islands and more importantly has recently dispersed into Europe. Since this snail is now considered an invasive species, its distribution is of growing parasitological interest as an alien intermediate host for various trematodes, particularly liver flukes. As part of ongoing surveillance for snail-borne diseases in Malawi, a population of O. viridis was first observed in May 2023, alongside an alarming presence of a human schistosome cercaria. This snail population later underwent detailed morphological characterisation with both snail and parasite identities confirmed upon DNA barcoding. This seminal observation triggered more extensive local snail surveys, finding 3 further populations in separated rice paddies, with further field-caught snails (n = 465) screened for infection and a selection used for repeated experimental challenges with miracidia from Schistosoma haematobium and Schistosoma mattheei. Although no field-caught (and experimentally exposed) snail was seen to shed schistosome cercariae, molecular xenomonitoring for schistosomiasis provided tangible evidence of putative transmission potential. Our first report of O. viridis here in Malawi, and more broadly in Africa, flags a need for increased vigilance for this invasive species alongside local clarification(s) of its transmission potential for trematodiases of either medical and/or veterinary importance.
ABSTRACT
BACKGROUND: Ocular surface squamous neoplasia (OSSN) is the most common cause of malignancy of the conjunctiva. Variable clinical presentation means that invasive malignant OSSN is often difficult to discriminate from other similarly presenting differential diagnoses which can be managed more conservatively. AIMS: Identification of clinical factors associated with a histopathological diagnosis of conjunctival squamous cell carcinoma (SCC). METHODS: Prospective consecutive case series of suspected OSSN cases presenting at two hospitals in Central Malawi over a 1 year period. A pro forma was completed assessing preidentified clinical variables. Suspected lesions underwent excisional biopsy followed by histopathological investigation. RESULTS: Fifty-eight patients were recruited. Mean age was 35.8 (range 22-62). 51 cases of histopathologically confirmed OSSN were found. 30 (50%) patients were confirmed HIV seropositive which rose to 86.67% in invasive SCC. Larger size of tumour (p=0.008), male gender (p=0.025) and HIV seropositivity (p=0.010) were associated with invasive SCC pathology. CONCLUSIONS: A clinicopathological study of OSSN has not previously been performed in Malawi. The association of HIV with SCC corresponds to previous reports from sub-Saharan Africa. A new finding in our study is a relationship between larger tumour size and invasive lesions confirmed by histopathology. When integrated into a clinical decision-making model, tumour area provides a simple clinical measure for ophthalmic practitioners to use in order to differentiate higher risk OSSN from more benign pathology. The higher risk lesions can subsequently be treated with greater surgical care and undergo closer follow-up.
