Evaluation of schistosomula lung antigen preparation and soluble egg antigen vaccines on experimental schistosomiasis mansoni

Abstract

Schistosomiasis causes significant morbidity and mortality worldwide. This study aimed to assess the effect of schistosomula lung antigen preparation (SLAP) and soluble egg antigen (SEA) on a murine schistosomiasis mansoni model. Ninety laboratory-bred male Swiss albino mice were divided into 6 groups. Two doses of the vaccine were given at 2-week intervals. All mice were subcutaneously infected with 80±10 Schistosoma mansoni cercariae 2 weeks after the last vaccination dose. They were sacrificed 7 weeks post-infection. Parasitological and histopathological studies were conducted to assess the effect of inoculated antigens (single or combined). The results showed that the combination of SLAP and SEA (combination group) led to a significant reduction in worm burden (65.56%), and liver and intestine egg count (59% and 60.59%, respectively). The oogram pattern revealed a reduction in immature and mature eggs (15±0.4 and 10±0.8, respectively) and an increased number of dead eggs in the combination group (P<0.001). In terms of histopathological changes, the combination group showed notably small compact fibrocellular egg granuloma and moderate fibrosis in the liver. A high percentage of destroyed ova was observed in the intestine of the combination group. This study demonstrates for the first time the prophylactic effect of combined SLAP and SEA vaccine. The vaccine induced a significant reduction in the parasitological and pathological impacts of schistosomiasis mansoni in hepatic and intestinal tissues, making it a promising vaccine candidate for controlling schistosomiasis.

Keywords: SEA; SLAP; Schistosomiasis; vaccine.

Fig. 1

Mean reduction rate of worm burden. Group I, non-infected non-immunized (Healthy control group); Group II, infected non-immunized; Group III, received Complete Freund’s adjuvant (CFA); Group IV, immunized with SLAP; Group V, immunized with SEA; Group VI, immunized with SLAP and SEA (combination group).

Fig. 2

Mean reduction rate of egg count per gram of liver and intestine tissues. Experimental conditions are indicated in the legend of Fig. 1.

Fig. 3

Histopathological study of the liver stained with hematoxylin and eosin stain (×200). (A) Normal hepatic lobular architecture. Bar=100 μm. (B) Cellular egg granuloma with intact central ovum (black arrow). (C–E) Egg granulomas with degenerated central ova (black arrows). (F) Fibrocellular egg granuloma with regular outline and degenerated central ovum (black arrow).

Fig. 4

Histopathological examination of the liver stained with Masson’s trichrome stain (×200). Bar=100 μm. (A) Deposition of fibrous tissue. (B) Mild fibrosis around the granuloma (+) (black arrow). (C) Marked fibrosis (+++) around the granuloma. (D–F) Moderate fibrosis (++) around the granuloma.

Fig. 5

Histopathological study of the intestine stained with hematoxylin and eosin (×400). Experimental conditions are indicated in the legend of Fig. 1. (A) Group I mice showing normal villus (black arrow). Bar=100 μm. (B) Group II mice showing many S. mansoni ova within the mucosa (black arrow). Bar=50 μm. (C) Group III mice showing S. mansoni ovum surrounded by a large number of inflammatory cells with a high percentage of eosinophils (yellow arrows). Bar=50 μm. (D) Group IV mice showing many S. mansoni ova within the mucosa with some intact (red arrow) and degenerated (yellow arrow) miracidia. Bar=50 μm. (E) Group V mice showing many S. mansoni ova within the mucosa (yellow arrow). Bar=50 μm. (F) Group VI mice showing many S. mansoni ova within the mucosa with mostly destroyed ova (yellow arrows). Bar=50 μm.