Early stage leucocytosis in Nigerian pigs experimentally infected with <i>Trypanosoma brucei</i>

Abstract

Sequential leukocyte changes associated with early phase of Trypanosoma brucei infection were investigated in indigenous Nigerian pigs. This was with the view to providing further hematological basis for effective chemotherapy of natural porcine trypanosomosis and to assessing the possible roles of leukocytes in determining tolerance to infecting trypanosomes in this early phase of infection, earlier believed to be a crisis period for most infected animals. The parameters measured included, daily body temperatures and weekly body weights as indicators of onset of clinical aspect of the disease as well as total and differential white blood cell (WBC) counts. After infection, parasitemia was first detected in the pigs on day 3 post-infection (PI) which was accompanied by onset of hyperthermia, manifested as rise in rectal temperatures on the same day and afterwards by undulating increase throughout the 40 day observation period. The weekly body weights however showed fluctuating increase throughout this period. The total WBC counts of infected pigs increased
progressively from the pre-infection value of 13.2±1.4 x 109 /L to the peak value of 38.5±12.6 x 109 /L (which corresponded to 191.7% increase above pre-infection values) on day 40 post infection (PI) while that of the control group only fluctuated within normal range. This was accompanied by an overwhelming, fluctuating surge in lymphocyte counts from the pre-infection value of 8.2±0.4 x 109 /L from day 1 to the peak value of 33.5±11.2 x 109 /L (corresponding to 308.5% increase above pre-infection values) on day 40 PI (P<0.05). The neutrophil counts also increased, though with a lesser intensity from the pre-infection value of 4.8±1.1 x 109 /L
to the peak value of 6.6±3.3 x 109/L (corresponding to 37.5% increase above pre-infection values) on day 17 PI (P<0.05) which is at variance to the known hematological derangement patterns in most trypanosome infections. These were also accompanied by persistent eosinopenia but fluctuating monocytosis in the infected group. It was concluded that leukocyte derangement in the early phase of T. brucei infection of pigs was characterized by overwhelming lymphocytosis and was attributed to strain specific trypanosome antigenic challenge leading to an  increased proliferation of immunocompetent cells into antibody and or lymphokine
producing cells. This is believed to be beneficial to the host as it could serve as determinant of host tolerance to infecting trypanosome and ability to survive this crisis phase of T. brucei infections.

Keywords: Pigs, leukocytosis, lymphocytosis, Trypanosoma brucei, early phase.