Relapse infection after chemotherapy in dogs experimentally infected with Trypanosoma brucei brucei

Studies on relapsing Trypanosoma brucei brucei infections in dogs after Berenil treatment revealed that the first relapse occurred 13 to 64 days after chemotherapy and 36 to 79 days after inoculation. A second relapse infection was observed in two dogs 43 and 60 days after a second Berenil treatment. During the aparasitaemic period following chemotherapy in four dogs, successful transmission (as evidenced by subsequent parasitaemia) following the intraperitoneal inoculation of homogenate of brain from two of the dogs into recipient rats was obtained. Transmission with blood collected just before the animals were sacrificed was, however, negative. Hornogenates of other organs (liver, spleen, eyes, testes, kidneys, heart and lymph node) were also non-infective. One dog inoculated with relapsed trypanosomes and treated with Berenil soon after showing parasitaemia was completely cured of the infection. It was considered that the brain is the source of relapse in T b brucei infection after Berenil therapy and that the relapse was not due to drug resistance.     

Pathogenicity of Trypanosoma brucei brucei in experimentally infected pigs.

An experimental infection of 4-to 5-month old pigs with a stock of Trypanosoma brucei brucei resulted in a high parasitaemia, anorexia, pyrexia and a decline in the packed cell volume by one third. Nervous sign of circling and wobbling of the hind legs occurred in one of the pigs which at necropsy revealed a very severe meningo-encephalitis and the presence of trypanosomes in the brain. These results confirm that T. b. brucei might cause a severe disease in pigs.     

Diminazene aceturate residues in the tissues of healthy, Trypanosoma congolense and Trypanosoma brucei brucei infected dogs

The tissue distribution and residue profile of diminazene aceturate was investigated in healthy dogs and in dogs infected with Trypanosoma congolense and Trypanosoma brucei brucei. The drug was administered at 3.5 mg/kg i.m. and tissue samples were taken post mortem from the animals at 48, 72, 120, 168 and 240 h after injection. The drug was distributed to various organs and tissues of the body with the highest concentrations occurring in liver and kidney. Higher drug levels were obtained in the tissues of healthy dogs compared with trypanosome infected animals except in the brain. The levels of residues in the healthy animals were significantly different (P less than 0.05) from those of the infected dogs. The drug residues were still detectable in the tissues of the animals 10 days after drug administration.     

Suppression of immune response to sheep red blood cells in rats experimentally infected with Trypanosoma brucei gambiense

A direct haemagglutination assay for antibodies to sheep red blood cells (SRBC) was used to assess the response of rats infected with Trypanosoma brucei gambiense. Whereas uninfected rats showed an efficient primary and secondary immune response to SRBC, trypanosome-infected rats displayed depressed antibody response starting about six days after infection. Infected rats failed to respond to a challenge dose of SRBC given 14 days after infection while uninfected control animals responded with an increased level of antibody production. These observations showed that T. b. gambiense infection inhibited both primary and secondary immune response to SRBC in rats. The result of this experiment is very important with regard to serological methods used to detect increasing levels of antibody production for diagnosis of diseases caused by bacterial and viral pathogens. In a concurrent trypanosome infection such increasing antibody levels would not be observed, leading to inaccurate diagnosis. Thus trypanosomiasis infection should be excluded under field conditions before the value of a serological diagnosis can be fully utilized.     

Parasitaemia and clinical manifestations in Trypanosoma brucei infected dogs.

Four dogs were infected with Trypanosoma brucei (Mkar strain) while another four were used as uninfected controls. Two of the dogs showed acute disease and died in the first wave of parasitaemia on days 7 and 8 post infection (PI) while the other two died from the sub-acute disease on days 24 and 28 PI corresponding to the second wave of parasitaemia. In the first wave of parasitaemia there was a sharp decrease in the packed cell volume, red blood cell, haemoglobin, total leucocytes, eosinophil, neutrophil and lymphocyte values, but during the period of low parasitaemia there was a slight recovery of the values of total leucocytes and lymphocytes although these and the other values showed a continuous decrease during the second wave of parasitaemia. In contrast, there was a consistent monocytosis in both acute and sub-acute diseases. The general picture was that of loss of condition, anaemia, leucopenia, monocytosis, ocular impairment, elevated temperature, pulse and respiratory rates, the difference between the acute and sub-acute diseases being in the degree of intensity. The degree of anaemia noted and the circulatory disturbances associated with the infection could have caused the death of all the infected dogs.     

Erythrocyte response to Trypanosoma brucei in experimentally infected dogs.

Trypanosoma brucei infection produced an acute and fatal disease in Nigerian mongrel dogs due to a rapidly developing anaemia. Infected dogs responded with increased reticulocytosis, which was not sustained with chronicity. In comparison the response to artificially-induced haemolytic anaemia was progressive, marked and sustained. The anaemia of T. brucei infection of dogs was either normocytic normochromic in acute infection or microcytic normochromic in chronic infection. Artificially-induced haemolytic anaemia was either macrocytic normochromic or normocytic normochromic. The erythropoietic potential of plasma in vivo in mice increased in T. brucei-infected dogs except at the terminal parasitaemia. The anaemia in Trypanosoma brucei-infected dogs is therefore initially responsive but becomes poorly involved with chronicity.     

Solubilization studies on the epicuticular antigens of Strongyloides ratti

Antigens on the epicuticular surface of Strongyloides ratti infective third-stage larvae (L3) were demonstrated by both ferritin-conjugated antibody and indirect fluorescent antibody techniques. The rat antibodies from immune serum that bind to these antigens were chiefly of the IgG2a subclass. Solubilization of these antigens by extraction with detergents, hypertonic salt, organic solvents and by freezing and thawing was limited as measured by the reduction in antibody binding to the epicuticle. The epicuticular antigens were resistant in situ to degradation by a variety of proteases, carbohydrases and lipase. Infectivity of the L3 in the rat was not reduced by prior sensitization with rat antibody. The epicuticular antigens are not completely species-specific since antibody from S. ransomi-infected pigs cross-reacted well with S. ratti L3 antibody. However, high levels of resistance to S. ratti could be induced in rats only by multiple inoculations of heat-killed S. ratti L3.     

Relapses in dogs experimentally infected with Trypanosoma brucei and treated with diminazene aceturate or isometamidium chloride

Twenty dogs of mixed local East African breeds were used. Five of the dogs were uninfected controls and 15 were infected with T. brucei (ILRAD 273). Five of the infected dogs were untreated controls, five were treated with a high curative dose of diminazene aceturate, (7 mg kg-1 body weight (wt.), and five were given a subcurative dose of isometamidium chloride (1 mg kg-1 body wt.). The drugs, given at 8 days post infection (d.p.i..), led to apparent recovery. The antibody titres, however, remained high in both groups and at 42-49 d.p.i. there was at least one relapse in each treatment group. Parasite populations from relapsed animals were more resistant to the drugs than the original infecting populations. The implications of these findings are discussed.     

The blood volumes and erythrokinetics of Ndama and Zebu cattle experimentally infected with Trypanosoma brucei.

The responses of susceptible Ndama and Zebu cattle to experimental infection with Trypanosoma brucei were compared using haematological, parasitological and radioisotopic methods. Animals of both breeds became anaemic, but this was more severe in the Zebu cattle, one of which died. Although the prepatent period was the same in animals of both breeds, the levels of the first and subsequent peaks of parasitaemia were higher in the Zebu. The anaemia was due to an accelerated rate of red cell break-down which was more marked in the Zebu cattle. Haemodilution was not a feature. There was no evidence of dyshaemopoiesis but iron reutilisation from degraded erythrocytes was impaired. The greater resistance of the Ndama to T brucei infection could not be attributed to the capacity of this breed to mount a more effective erythropoietic response than the Zebu.     

A soluble immunosuppressor substance in spleen in deer mice infected with Trypanosoma brucei.

A soluble substance that blocks B-cell response was extracted from spleen of deer mice (Peromyscus maniculatus) chronically infected with Trypanosoma brucei. Immunosuppressor activity of this substance was demonstrated by plaque-forming cell assays of spleen cells from Swiss/Webster mice inoculated with sheep red blood cells and simultaneously given the suppressor substance, and of spleen cell cultures treated with sheep red blood cells and suppressor substance. Studies by light and electron microscopy of spleen of immunosuppressed Swiss/Webster mice showed that the suppressor substance blocks germinal center formation and prevents plasma cell differentiation in the red pulp cords.     

Suggested dosage rates of melarsoprol in the treatment of mice experimentally infected with Trypanosoma brucei gambiense

One group of BALB/c mice infected with a highly virulent strain of Trypanosoma brucei gambiense were treated intraperitoneally with three series of three injections (each injection of 10 mg/kg) of Mel-B separated by seven days of rest, while a second group was treated once by a single injection All the Mel-B treated mice in both experiments were negative for parasites when examined using either the wet blood film or buffy coat methods, but were intermittently PCR positive during the sampling period. We encourage the use of a repeat negative PCR test over a one month period in combination with corroborative clinical and parasitological investigation to be suggestive of cure in experimental animals previously infected with trypanosomosis. In view of the exorbitant costs of Mel-B and its extreme toxicity, we recommend that Mel-B be given as one course of two injections (each equivalent to 10 mg/kg) separated by 2 d of rest in experimentally infected rodent models.     

The pathogenesis of anaemia in goats experimentally infected with Trypanosoma congolense or Trypanosoma brucei: use of the myeloid:erythroid ratio

The present study examined the development of anaemia in Small East African goats experimentally infected with Trypanosoma congolense or Trypanosoma brucei. Experimental goats received a primary trypanosome challenge on day 0, treated with diminazene aceturate on day 49 and received a secondary trypanosome challenge on day 77 of the 136-day experiment. Both primary and secondary challenges were characterised by reduced peripheral erythrocyte counts, fall in packed cell volume (PCV), hypohaemoglobinaemia and reductions in the myeloid:erythroid ratios (M:E) compared with the uninfected goats. The progressive reduction in the M:E ratios denoted increased erythrogenesis in response to increased destruction of erythrocytes in blood by infecting trypanosomes or their products. The more rapid fall in M:E ratio in T. congolense infections shows that this parasite causes more severe clinical pathological effects in goats than T. brucei.     

Massive increase in splenic germinal centres of chickens experimentally-infected with Trypanosoma brucei brucei

Domestic chickens infected with Trypanosoma brucei brucei developed a latent parasitaemia which lasted for one year. Six distinct variable antigen types were isolated. Spleens from infected birds were studied histologically at different stages of the infection. Trypanosome infection produced a progressive increase in the number of germinal centres during the early stages of the infection. Peak numbers of germinal centres were reached in the spleen at Day 84 after which the numbers were maintained during an active infection. A tenfold increase in the number of germinal centres was found in trypanosome-infected birds compared to controls. No splenomegaly was observed. Lymphoid cells of the caecal tonsil and the thymus remained apparently normal during the course of infection. Chemotherapeutic termination of infection with berenil resulted in an initial increase in the number of germinal centres. A gradual return to normal level was observed on Day 100 post cure. It is suggested that the development of such a large number of germinal centres reflects the bird's response to the elaboration of a succession of trypanosome variable antigens.     

The response of pigs experimentally infected with Trypanosoma brucei to isometamidium chloride therapy and the relation to nutrition.

Growing pigs were placed on feeds with high (Group A), medium (B) and low (C) dietary energy and were infected with a virulent stock of T. brucei. Eight weeks later, the infected pigs were treated with isometamidium chloride at 1 mg/kg live weight and all pigs were subsequently placed on a high energy diet to investigate their response to therapy. Clearance of T. brucei from blood was completed 72h after treatment. There was no evidence of relapsed infection up to eight weeks after treatment. Red blood cell parameters returned to normal four to six weeks after treatment with responses being fastest in Group A, B and C had gained about two-thirds of the live weight gains of their non-infected pair-fed controls. It appears that the retarded weight gain as a result of the infection persisted after therapy since drug-treated pigs did not gain as much weight as their non-infected controls.     

Study on the antioxidant status of rats experimentally infected with Trypanosoma evansi

The antioxidant status of rats experimentally infected with Trypanosoma evansi isolated from a camel was studied using established parasitological, haematological and biochemical methods. The results indicated that infections in all rats resulted in a fulminating parasitaemia. Changes in blood parameters in T. evansi-infected rats indicated leukocytosis and a macrocytic hypochromic anaemia. A degree of anisocytosis was also observed. The activities of plasma glucose-6-phosphate dehydrogenase and glutathione peroxidase in whole blood of infected rats were significantly higher (p<0.05 and p<0.001, respectively) compared with control. No statistically significant difference was observed in the activity of superoxide dismutase in infected and control rats. Results obtained indicated that trypanosomosis caused oxidative stress and induced antioxidant enzymes.