| dc.description.abstract | Trypanosomiasis in animals is associated with immunosuppression that manifests
clinically as increased susceptibility to opportunistic infections. Although
immunosuppression has been shown to result from depression of antibody
production and suppression of cell-mediated immunity, in some cases there is no
obvious impairment of these functions. For effective immune response, all of the
three effector systems; the mononuclear phagocytic system, the polymorphonuclear
phagocytic system, and the complement cascade, must be intact. Polymorphonuclear
leucocyte (PMN) function was assessed in trypanosome-infected
sheep to establish its possible contribution to lowering of body defence.
Trypanosoma congolense (Broden, 1904) and T brucei (Plimmer and Bradford,
1899) were obtained from American Type Culture Collection, Maryland USA,
and amplified in rats. Fourteen castrated, eight-month old, male sheep were
purchased locally. Initially, four Suffolk x Finnish sheep were inoculated with
T congolense while two acted as controls. Later, six North Country Cheviot
sheep were inoculated with T brucei while two acted as controls. Each infected
sheep received eight million trypomastigotes intravenously. The sheep were
monitored daily for clinical disease and tests of PMN function were assessed
over two months. PMNs were isolated from ethylenediamine tetra-acetic acid
anti-coagulated blood obtained from each sheep and superoxide anion production
assessed by cytochrome C reduction, every second week in the first experiment
and weekly in the second experiment. In addition, heparinized blood was
obtained weekly and used to perform nylon wool adherence and phagocytosis of
opsonized zymosan in the second experiment.
Although sheep infected with T congolense developed parasitaemia, there were
no clinical signs of trypanosomiasis, no gross or microscopic lesions and results
of cytochrome C assay were not significantly different between infected and
control sheep. Sheep infected with T brucei developed parasitaemia, clinical
signs of trypanosomiasis and alteration in PMN function. PMNs obtained from
infected sheep had significant decrease in superoxide anion production (p<0.01)
and nylon wool adherence (p< 0.01), but enhanced phagocytosis of opsonized
zymosan (p< 0.01).
Clinical disease of T brucei infection in sheep was characterized by pyrexia,
anorexia, weight loss, anaemia, and inflammatory edema of skin of the head,
neck, brisket, distal limbs, and tail. At the end of the trial, the sheep were
euthanised and examined for lesions. There was edema of the skin and enlargement
and edema of superficial lymph nodes. Microscopic lesions were observed
in the skin, superficial lymph nodes, spleen and kidneys. Skin lesions consisted
of severe edema accompanied by diffuse perivascular and periadnexal dermatitis,
perineuritis, lymphangitis, distension of lymphatic vessels with fluid, and
lymphatic thrombosis in the dermis and subcutis. Inflammatory reaction
extended deep into subcutis leading to severe panniculitis and myositis. Inflammatory
cells were mainly macrophages, plasma cells, and lymphocytes although
polymorphonuclear leucocytes were also present. Numerous trypanosomes were
seen in skin lesions. Superficial lymph nodes had severe capsular lymphadenitis
and lymphoid hyperplasia. The spleen had lymphoid hyperplasia. Lesions in the
kidney consisted of mild to moderate glomerulonephritis and a few tubular casts.
In summary, sheep infected with T congolense for two months were not
clinically sick and had no alteration in PMN function. Sheep infected with T
brucei for two months .were clinically sick and had significant alteration in PMN
function. Such alteration may be responsible for the increased occurrence of
opportunistic infections in trypanosomiasis. Microscopic appearance of skin
lesions described in T brucei-infected sheep confirms that the inflammatory
reaction is similar to that previously described in other organs. | en |
