Abstract
Neurocysticercosis is a frequent parasitic infection of the human brain, occurring in most of the world, and requires imaging of the brain to diagnose. To determine the burden of disease and to simplify diagnosis, a field-friendly rapid lateral flow (LF) based antibody screening test was developed. The assay utilizes novel nano-sized up-converting phosphor (UCP) reporter particles in combination with a portable lightweight analyzer and detects antibodies in serum samples reactive with bacterial-expressed recombinant (r) T24H, a marker for detecting neurocysticercosis cases. Three sequential flow steps allow enrichment of antibodies on the Test (T) line and consecutive binding of protein-A coated UCP reporter particles. Antibody binding was determined by measuring 550 nm emission after excitation of the UCP label with a 980 nm infrared (IR) diode. Clinical sensitivity and specificity of the assay to detect cases of human neurocysticercosis with 2 or more viable brain cysts were 96% and 98%, respectively, using a sample set comprised of sera from 63 confirmed cases and 170 healthy parasite-naïve non-endemic controls. In conclusion: Proof-of-principle, of a rapid UCP-LF screening assay for neurocysticercosis was demonstrated. The assay utilized bacterial-expressed rT24H as a potential alternative for baculovirus-expressed rT24H. Performance of the UCP-LF assay was excellent, although further studies need to confirm that bacterial expressed antigen can entirely replace previously used baculovirus antigen. In addition, the increasing availability of commercial sources for UCP reporter materials as well as the accessibility of affordable semi-handheld scanners may allow UCP-based bioanalytical systems for point-of-care to evolve at an even faster pace.
Highlights
Cysticercosis is a tissue infection caused by hatched oncospheres, a larval form of the pork tapeworm Taenia solium
The general protocol applied for the up-converting phosphor (UCP)-lateral flow (LF) assay used for the majority of the experiments in this study, implied a dilution of sera in assay buffer such that 1 mL undiluted serum was delivered to the LF strips during the first flow step of the consecutive flow (CF) protocol (Fig. 1)
All assays were performed with the same amount of UCP label, and T-signal values were normalized to the highest Tsignal measured with the 100 units per mL (Units) sample; achieved with the LF strips containing an rT24H density of 100 ng, the 200 ng strips scored only a slightly lower signals
Summary
Cysticercosis is a tissue infection caused by hatched oncospheres, a larval form of the pork tapeworm Taenia solium. The eggs release oncospheres that are able to invade the intestinal wall and circulate through the bloodstream. This can result in neurocysticercosis, invasion of the nervous system and the formation of cysts in the brain, which is a major cause of adult acquired epilepsy and other neurological morbidity in many areas of the world [1,2]. Diagnostic imaging of the central nervous system is required to confirm the diagnosis and the type of disease [3]. The availability of a rapid serological diagnosis that targets stage-specific antibodies for human cysticercosis is considered very helpful in control programs for estimating the burden (sero-prevalence) of disease in susceptible population groups. A low-cost rapid diagnostic test could be applied to determine seroprevalence rates in pigs to assess interruption of transmission
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