Apr

17

Dermatophilosis - Tick Borne

April 17, 2009 |

The description of the disease in this article has a strange familiarity.

From Here :
Dermatophilosis is an exudative dermatitis that affects mainly ruminants, but also other species including humans.
The aetiological agent of dermatophilosis is the branching filamentous actinomycete bacterium Dermatophilus congolensis.
Various forms of the disease are recognized in different species, and there is considerable variation in the clinical appearance of the disease and in the affected areas of the body.
AND
Dermatophilus congolensis itself is not highly pathogenic; combinations of factors predispose animals to infection. For example, malnutrition at the start of the rainy season can affect the course of infection, and infection is initiated at sites where the skin’s defensive barriers, comprising sebum, skin surface antibodies and stratum corneum, have been damaged by intense rainfall and/or by mechanical trauma.
Rainfall also has a role in dispersal of the organism from crusts to healthy skin and it triggers activity in arthropod populations.
Haematophagous flies cause skin damage and initiate inflammation at feeding sites.
The resulting exudate attracts flies that act as mechanical vectors for D. congolensis, and provides a growth medium for the bacterium.
The bacterium proliferates by growth of hyphae that undergo transverse and longitudinal division
to produce filaments containing cocci (see Poster, this issue).
Motile, flagellate cocci are released from wet crusts and these establish new sites of infection on the
same animal or are transmitted to new hosts.
Dermatophilosis crusts characteristically comprise alternating layers of keratinocytes, vesicles of serous exudate and infiltrates of neutrophils, giving a palisaded appearance in stained sections. This suggests that crusts are formed by repeated cycles of epidermal proliferation, bacterial invasion, release of exudate into vesicles and influx of neutrophils.

The dermis underlying chronically infected epidermis contains accumulations of neutrophilis, mononuclear cells and plasma cells (Fig. 2). The density of the cellular infiltrate correlates with lesion severity. This infection provides unique opportunities to examine immune responses in the skin and the influence of tick infestation on immune responses to a second pathogen.


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