Are Alternative Sources of Parasitic (Cysticercal) Antigens Necessary for Diagnosis of Neurocysticercosis?

In their recent article, Bueno et al. (1) evaluated antigenic extracts from Taenia crassiceps (Tcra) and Taenia solium (Tso) metacestodes in cerebrospinal fluid (CSF) and serum samples of neurocysticercosis (NC) patients for diagnosis of NC and attempted to investigate whether serum alone could be used for seroepidemiological purposes in the diagnosis of NC. The authors observed a high specificity of the immunoassays when either Tcra or Tso in CSF was used but a significant difference when serum samples were used. The study concluded that Tcra could be used in immunoblotting for confirmation of enzyme-linked immunosorbent assay (ELISA) results.

Do we need alternative sources of parasites for preparing cysticercal antigens for the immunodiagnosis of NC? It is believed that obtaining Cysticercus cellulosae from naturally infected swine would be a simpler and more economical way to prepare antigens than obtaining cysticerci from T. crassiceps. In underdeveloped and developing countries, pig rearing is a common activity. Pigs become infected naturally by grazing in open areas where humans defecate. Cost-wise, a kilogram of (infested) pork would cost approximately Rs.25/- (US $1 = INR 45). Therefore, one could easily obtain infested pork and prepare cysticercal antigens. Earlier, several researchers evaluated various antigenic preparations (either purified, partially purified, or crude) of C. cellulosae only and obtained a high specificity (4, 6, 8). Qualitative differences between C. cellulosae from porcine and human sources and antigenic variation in C. cellulosae obtained from infested pigs from different regions of India have been observed (5). Moreover, both definitive and intermediate hosts are different in both Taenia species. Therefore, it would be appropriate and reasonable to employ antigens of C. cellulosae in the diagnosis of NC.

For immunodiagnosis of NC, detection of both antigen and antibody in CSF or in CSF and serum, and not in serum alone, has been suggested since de novo synthesis of anticysticercal antibodies in the central nervous system (CNS) compartment has been demonstrated in cases of NC (7). Therefore, the objective of Bueno et al. (1) to evaluate serum alone for seroepidemiological purposes may result in the detection of cases of systemic cysticercosis and the underdiagnosis of cases of NC in areas of endemicity in Brazil.

The differential diagnosis of chronic meningitis to determine whether the infection is NC or tuberculous, cryptococcal, or carcinomatous meningitis has always been problematic because these infections are highly endemic in many underdeveloped and developing nations and various clinical manifestations of NC overlap those of other diseases of the CNS (2). Therefore, it would have been ideal if the authors had assessed the specificity of Tso or Tcra antigens in CSF samples from patients with proven cases of tuberculous, cryptococcal, or carcinomatous meningitis.

Antigenic identity between peptides of ≤23, 39, 85 to 77, and 97 kDa of Tso and peptides of ≤62, 74, 109, 121, and 131 kDa of Tcra has not been elucidated. Therefore, studying the antigenic relationship between specific antigenic components of Tso and Tcra (see Table 2 in reference 1) would enhance the specificity of immunoassays in the immunodiagnosis of NC by purifying them.

It is essential that future studies offer appropriate measures of control and prevention of NC (3). For control of NC, it is necessary to diagnose the disease accurately by using purified parasitic antigens prepared from pools of cysts derived from different regions of endemicity of the world, since parasites are known to exhibit antigenic variation (5, 9). NC could be prevented by simply breaching the life cycle of the parasite, and that is achieved by the education of the population, the adoption of strict hygienic practices in their life style, the elimination of pig grazing in open areas where defecation has occurred and, finally, the cessation of pork consumption.