A Study on the Nature of Association between Demodex Mites and Bacteria Involved in Skin and Meibomian Gland Lesions of Demodectic Mange in Cattle

Abstract

The nature of association between Demodex mites and bacteria involved in bovine demodectic mange lesions and the normal flora inhabiting the skin of noninfected animals was investigated. Demodex bovis and D. ghanensis mites were isolated from the infected purulent material extracted from skin and meibomian gland lesions, respectively. The mites could not be demonstrated in skin brushings or impression smears from the eyes of noninfected cattle. Pathogenic bacteria (Staphylococcus aureus and Streptococcus pyogenes (Group A)) and opportunistic organisms (Proteus vulgaris, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Trueperella pyogenes) were isolated from skin lesions of demodectic mange, and Moraxella bovis and Staphylococcus aureus were isolated from meibomian gland lesions. Bacillus subtilis, Escherichia coli, Proteus vulgaris, Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus pyogenes (Group A) were isolated from skin brushings from noninfected cattle. The nature of association between Demodex mites and bacteria in demodectic mange lesions is synergistic and of equal significance. Pathogenic and opportunistic bacteria facilitated the establishment of Demodex mites in the lesions produced and provided an excellent microclimate for the mites to propagate and reproduce, resulting in severe and progressive disease. The "high-turnover" granulomatous reaction which characterized the histopathological changes proved that Demodex mites and associated bacteria were persistent and immunogenic.

Figure 1

A cow infected with demodectic mange, showing pustules involving the neck, and nodules scattered over the whole body. Note folding of the skin at the base of the neck.

Figure 2

Pustules and crust-covered lesions of demodectic mange involving extensive areas of the body of a heifer. Note marked wrinkling and folding of the skin.

Figure 3

Simultaneous skin and meibomian gland demodicosis. Note swelling of the eyelids and nodules on the upper eyelid arranged in a linear fashion.

Figure 4

Numerous Demodex bovis mites and its different developmental stages, pus, and cell debris in a crushed specimen of infected purulent material extracted from skin lesions of demodectic mange. Scale bar: 70 μm.

Figure 5

Demodex ghanensis mite in infected material extracted from meibomian gland lesions of demodectic mange in a cow. 20% potassium hydroxide solution. Scale bar: 50 μm.

Figure 6

Section from the skin of a cow, showing invasion of a hair follicle with Demodex bovis. Note dilatation of the hair follicle bulb, mites (M), and slight infiltration by inflammatory cells in close proximity of the hair follicle. Haematoxylin and Eosin. Scale bar: 100 μm

Figure 7

Sections from the eyelid of a cow, showing invasion of the meibomian gland with Demodex ghanensis. Note hemorrhage, exudation, and damage of the proximal part of the main collecting tubule (asterisks), marked infiltration with inflammatory cells, dilatation of the main collecting tubules, and Demodex ghanensis mite in the main collecting tubule (black arrow). Haematoxylin and Eosin. Scale bar: 120 μm.

Figure 8

Saccular distension of adjacent hair follicles with Demodex bovis mites and associated bacteria, forming large colonies of demodectic mange (bladder-like cysts) in skin sections from an infected cow. Note extremely stretched and jagged epithelial lining (black arrows). Haematoxylin and Eosin. Scale bar: 200  μm.

Figure 9

Section from an infected meibomian gland, showing D. ghanensis mites (asterisks) in the glandular acini, granulomatous reactions in the infected acini, and proliferation of connective tissue surrounding the granulomas (white arrow head). Haematoxylin and Eosin. Scale bar: 200  μm.