Growth inhibitory effect of selected medicinal plants from Southern Ethiopia on the mycelial phase of Histoplasma capsulatum var. farciminosum

Abstract

Background: Epizootic lymphangitis is an infectious and chronically debilitating disease of the equines. Histoplasma capsulatum var. farciminosum, a thermally dimorphic fungi, is the causative agent for the disease. In Ethiopia, the disease significantly affects carthorses, posing threats to animal welfare, and resulting in substantial economic losses. Limited availability of widely accessible antifungals in addition to the chronic nature of the disease is the major challenge against management of epizootic lymphangitis. This study aimed to assess the in vitro efficacy of specific local medicinal plant extracts against the mycelial phase development of H. capsulatum var. farciminosum in southern Ethiopia. The leaves of Xanthium strumarium, Kanda (Family Rubiaceae), Croton macrostachyus (Bisana in Amharic), and Centella Asiatica (Echere waye as a local name in Zeyissegna) that are traditionally used for the treatment of different skin ailments were collected and extracted for the in vitro trial.

Results: The study revealed that methanol extracts of Xanthium strumarium, Kanda, Croton macrostachyus, and Centella Asiatica, at minimum inhibitory concentrations of 1.25 mg/ml, 2.5 mg/ml, 2.5 mg/ml, and 5 mg/ml, respectively, inhibited the growth of H. capsulatum var. farciminosum.

Conclusion: This in vitro finding could serve as significant preliminary data in the exploration of effective alternative treatment options for epizootic lymphangitis. This study provides a crucial foundation for further research aimed at determining the chemical components and in vivo effectiveness of these plant extracts against both the mycelial and yeast forms of Histoplasma capsulatum var. farciminosum.

Keywords: Epizootic lymphangitis; Hawassa; Histoplasma; In vitro; Medicinal Plants; Mycelia.

Fig. 1

Characteristic Histoplsma capsulatum variety farciminosum yeast cells from clinical cases stained with Wright stain: (A) from Mid (black thin arrows shows yeast cells; flat arrows indicate macrophage engulfed yeast cells; flat and indented arrows shows neutrophils whereas red arrow indicates budding yeast cell); (B) Early (flat arrows indicate macrophage engulfed yeast cells whereas thin arrows indicate yeast cells and (C) advanced stages of the disease (arrows indicating yeast cells)

Fig. 2

Characteristic cutaneous epizootic lymphangitis lesion seen during the study: (A) donkey; (B) horse and (C) mule. Arrows showing ulceration, cording of the lymphatics and the skin with fistulation (in A) and ulcerating nodules as in B and C where most of the nodules coalesced

Fig. 3

Microscopy of Gram-stained smears of Histoplsma capsulatum variety farciminosum from 12th weeks of incubation (multiple small arrows indicating a septate hyphae bearing rounded (sometimes speculated) macroconidia whereas indented flat arrows show microconidia

Fig. 4

Pictorial representation of growth inhibitory effects of Xanthium strumarium (A), Kanda (B), Croton macrostachyus (C), Centella Asiatica (D), and positive control (ketoconazole) (E) at different concentrations. The 1–8 numbers (from A to D) indicates plant extract concentrations ranging from 10 mg/ml, 5 mg/ml, 2.5 mg/ml, 1.25 mg/ml, 0.625 mg/ml, 0.3125 mg/ml, 0.156 mg/ml, and 0.78 mg/ml, respectively whereas the 1–7 numbers (E) indicate the Ketoconazole concentration ranging from 0.8 mg/ml, 0.4 mg/ml, 0.2 mg/ml, 0.1 mg/ml, 0.05 mg/ml, 0.025 mg/ml, and 0.0125, respectively

Fig. 5

Portrayal of plants used in this study: (A) Kanda (family Rubiaceae); (B) Xanthium strumarium; (C) Croton macrostachyus (Bisana); and (D) Centella Asiatica (Echere waye)