Infectivity and virulence in a serodeme of Trypanosoma vivax

The course of infection by a mouse-adapted Trypanosoma vivax was studied. Serological variants were isolated from sheep and their infectivity and virulence were studied in mice and sheep. Isolates obtained in the early stage of the infection were highly virulent while isolates obtained at the terminal stage of the infection were found to be extremely virulent in both mice and sheep. Trypanosoma vivax organisms isolated in between these series of parasitaemias were of low to moderate virulence in both groups of animals. The degree of virulence exhibited by each isolate was closely related to the viability of the organisms. The success of making clones was equally found to be related to the virulence of the isolates.     

Morphological changes of Trypanosoma vivax in mice

Morphological changes were observed in the blood forms of Trypanosoma vivax strain Y486 in mice on Days 12-13 of infection, following the peak parasitaemia. During this period elongate trypomastigotes, 25-40 micron long, were observed, most showing an anterior movement of the kinetoplast towards the nucleus and some having a blunt posterior end. In a few parasites a complete transformation to the epimastigote form, 40-42 micron long, was observed. Small sphaeromastigotes were also present, especially in the fine capillaries of various organs. Smears and electron microscopy suggested the presence of extra-vascular forms in the spleen.     

Effect of isometamidium on Trypanosoma congolense infectivity

Isometamidium chloride (Samorin, RMB, England) is a widely used and highly effective trypanocide for the treatment of bovine trypanosomiases. However, the appearance of isometamidium-resistant populations of T. congolense in Africa makes it necessary to develop methods for the rapid and reliable detection of drug resistance in the laboratory. Currently available tests are time-consuming and/or expensive. In the present study, the short-term in vitro incubation of trypanosomes in a range of isometamidium concentrations and the infectivity of the parasites in mice has been assessed. A series of T. congolense isolates were used which were known to differ in their in vivo sensitivity to the drug. The results showed a close correlation between the known level of resistance and the capability of trypanosomes to remain infective after incubation in isometamidium. Thus isolates displaying a high level of resistance in vivo remained infective following incubation in higher concentrations of drug. This assay may provide a simple and reliable method for detecting drug resistance in T. congolense.     

Association of infectivity, parasitaemia and virulence in a serodeme of Trypanosoma congolense

Quantitative methods were adopted to study the course of Trypanosoma congolense infection in mice and goats. The ease of initiating infection with a single organism (clone) was found to show a smooth correlation with the virulence of 24 isolates. Virulence of T. congolense was found to be directly related to the degree of viability of the parasite but inversely proportional to the capacity of the host to limit parasitaemia. Isolates obtained from the goat in the early stage of the infection were found to be highly infective but moderately virulent; subsequent isolates were of low infectivity and low virulence. Organisms obtained at the terminal stage of the infection were highly virulent. Generally, the highly virulent clones produced rapidly high parasitaemia and mortality in the host. The low virulence clones were characterised by low parasitaemia but very pronounced remission of trypanosomaemia.     

Effect of Trypanosoma vivax infection on semen characteristics of Yankasa rams.

Twelve Yankasa rams aged between 2 1/2 and 3 years with good semen characteristics were used in this 15-week study. Six rams were infected with Trypanosoma vivax, while six served as controls. The infected rams developed chronic trypanosomosis accompanied by fluctuating pyrexia, lethargy, anaemia, scrotal oedema and cachexia. There was a drastic and progressive deterioration in semen quality in all infected rams manifested by a decrease in volume or cessation of semen production, oligozoospermia, a sharp decrease in progressively motile sperm, elevated numbers of dead (eosinophilic) sperm and 100% morphological abnormalities of sperm in most animals. The rams were all deemed unfit for breeding by 3 weeks post-infection. Uninfected rams were healthy and had good semen characteristics throughout the investigation. The results show that rams infected with T. vivax may become infertile within a short interval due to rapid deterioration of semen characteristics and this trypanosome species may be an important causative agent of infertility in endemic areas.     

Effect of Trypanosoma vivax infection on energy and nitrogen metabolism of west African dwarf goats

A study was conducted using 32 mature 22-kg West African Dwarf Goats to measure the effect of Trypanosoma vivax infection on energy and nitrogen metabolism. Sixteen goats were infected intravenously with 14 X 10(6) T. vivax. Sixteen control goats were sham-injected. Digestibility and metabolizability of energy and N balance were measured for each goat. Heat production and energy balances were measured per treatment group from 1 wk before infection to 6 wk after infection. Goats were fed alfalfa pellets (10% above maintenance). Treated goats had a reduced (P less than .05) packed cell volume (38 to 40% before infection vs 20 to 25% 6 wk after infection) and an increased (P less than .05) rectal temperature. Log parasitemia/ml was about 6.0 to 6.2. Parasitized goats showed increased urine creatinine excretion at wk 2 postinfection. After infection, feed intake was reduced (about 15%; P less than .05) and greater variability in intake was noted. Treated and control goats had similar N output and energy output in urine. Metabolizability of energy intake was similar at 42.7 vs 42.1% in treated vs control goats, respectively. Heat production in infected goats was increased by about 15%. Treated goats lost more weight and had a lower N balance than control goats (P less than .05). The calculated maintenance energy requirement for infected goats (464 kJ ME/kg.75) was 25% greater than for control goats (375 kJ ME/kg.75).     

Leucopenia in Trypanosoma vivax infection of sheep

Experimental Trypanosoma vivax infection of sheep produced a moderate leucopenia associated with a lymphopenia and eosinopenia. The total white blood cell counts of adult mice were not significantly depressed when inoculated with plasma from T. vivax-infected sheep. These observations suggested that the plasma of the infected sheep did not have a factor which could depress leucopoiesis in vivo.     

Experimental infection of the Guyanese zebu with Trypanosoma vivax

The Guyanese strain of Trypanosoma vivax is pathogenic for the local Brahman zebu; the experimental infection of 19 one-year old cattle was followed by a moderate and transitory fever, a drop in packed cell volume (PCV) and a quick and marked weight loss of 10 to 17 kg one month after as compared to the 16 non-infected animals. Other symptoms were associated with the parasitaemia: diarrhoea, swollen haematic glands on the neck and the flank, lachrymation, weakness. Despite a trypanocidal treatment injected one month post-infection, one animal died and the weight losses of others were not compensated for three months later. The particular susceptibility of weaning animals is discussed as well as its implications in the control of trypanosomosis.     

Babesia equi and Trypanosoma vivax infections in donkeys

Six donkeys (Equus asinus) were purchased locally. To screen them before and during Trypanosoma vivax infection, thin and thick blood smears, temperature, haematocrit centrifuge technique (HCT), packed cell volume (PCV), white blood cell counts, and indirect immunofluorescent antibody test (IFAT) were done for Babesia equi. For the IFAT, an anti-horse conjugate was used. In spite of patent B. equi or T. vivax parasitaemia, the donkeys' temperatures remained below 38.5 degrees C; PCV was depressed more in B. equi infection than in T. vivax infection. Four out of the 6 donkeys had B. equi antibodies while 2 of them had detectable parasitaemia. Treatment with either Berenil or Imizol cleared the detectable B. equi parasitaemia, and IFAT was negative at 35-45 days post treatment. However, relapses occurred within 60-70 days after the treatment. In 2 circumstances serological titres were below 1:40 (negative) while there was detectable parasitaemia.     

Effect of novidium (homidium chloride) chemotherapy on genital lesions induced by Trypanosoma vivax and Trypanosoma congolense infections in Zebu bulls

Zebu bulls chronically infected with Trypanosoma vivax and T. congolense were treated at the 12th week post-infection with novidium and slaughtered at different times after treatment to determine histological evidence of healing of the genital lesions. Though trypanosomes disappeared from the blood soon after chemotherapy, there was incomplete resolution of genital lesions even 10-18 weeks later. Where there is severe degeneration of the testes and epididymes chemotherapy may be ineffective in leading to regeneration and therefore infertility problems may persist in bulls with chronic trypanosomiasis which are later subjected to chemotherapy.     

Action of isometamidium chloride on the insect vector form of Trypanosoma vivax

The effect of isometamidium chloride upon developing and mature Trypanosoma vivax occurring in Glossina palpalis palpalis flies was evaluated. Newly emerged G p palpalis flies were infected with T vivax by allowing them to feed on parasitaemic animals. Two experiments were conducted and in each the flies were divided into two groups. One group of infected flies was fed in vitro through a membrane on defibrinated cow blood containing isometamidium chloride at 0.1 mg ml-1, after which they were dissected and examined for trypanosomes, and the other group was fed in the same way on unmedicated blood. The results showed that out of a total number of 129 flies which fed on medicated blood, none was infected, while 55 out of 127 flies which fed on unmedicated blood were infected. The results indicate that isometamidium chloride eliminated the insect vector form of T vivax. These findings are of potential significance in the control of trypanosomiasis in the field, particularly in the operation of the sterile insect technique.     

Comparative infectivity for axenic and specific-pathogen-free chickens of O2 Escherichia coli strains with or without virulence factors

Adhesion to epithelial respiratory cells, iron acquisition, and production of K1 polysaccharide capsules have been proposed as potential virulence factors of avian Escherichia coli. These factors were studied by inoculating groups of axenic or specific-pathogen-free (SPF) chickens intratracheally with O2 E. coli strains after previous challenge with a wild strain of infectious bronchitis virus (IBV). In all experiments, the association between IBV and an E. coli strain endowed with the three virulence factors previously mentioned resulted in the most severe pathological effects, as measured by mortality, weight gains, lesions, and reisolation of E. coli from internal organs. An E. coli strain devoid of virulence factors was able only to induce mild pathological effects restricted to the respiratory tract when combined with IBV. Both E. coli strains were more invasive in axenic chickens than in SPF chickens. These results confirm the probable involvement of the three factors studied in the pathogenic properties of avian E. coli. This model can be used to assess the role of virulence factors, by comparing pairs of positive and negative isogenic strains.     

Study on the susceptibility of Sahel goats to experimental Trypanosoma vivax infection

Sahel goats, also known as Borno whites are found in the northern semi-arid, tsetse free Sahel region of Nigeria. They are transported alongside cattle from this zone to all other zones in the country, including the tsetse-infested zones, for commercial purposes and are kept for some time in these tsetse-infested zones until they are sold. This study therefore assessed the susceptibility of this breed of goats to trypanosome infection and its response to treatment with Berenil. Six bucks were inoculated intravenously with Trypanosoma vivax through the jugular vein while two served as uninfected control. The mean pre-patent period was 4.5 days and increasing parasitaemia followed the establishment of infection. Onset of parasitaemia was associated with increase in rectal temperature in all the infected goats and the temperature peak coincided with the only parasitaemic peak second week post-infection. The infected goats were treated with Berenil (Hoechst, Germany) 3.5mg/kg body weight at 4 weeks post-infection. The packed cell volume (PCV) continued to fall from a mean 30.73+/-0.01% pre-infection to a mean 13.21+/-0.18% at 1 week post-treatment. Deaths were recorded for 4 of the infected goats 1 week post-treatment while the remaining two died 2 weeks post-treatment, not responding to treatment.     

Pathological changes in male genitalia of cattle infected with Trypanosoma vivax and Trypanosoma congolense

Samples for histological studies were taken from the genitalia of 14 bulls (five infected with Trypanosoma vivax, five with T. congolense and four uninfected control animals), slaughtered 12, 22 or 30 weeks post-infection. Infection with Y58 strain of T. vivax and strain 2295 of T. congolense caused various grades of lesions in the male reproductive organs, especially the testes and epididymides. T. congolense produced more severe degenerative changes than T. vivax. It is concluded that in long-standing cases, the result of trypanosome infection is either serious infertility or even sterility.     

Susceptibility of N'Dama cattle to experimental challenge and cross-species superchallenges with bloodstream forms of Trypanosoma congolense and T. vivax.

Susceptibility to Trypanosoma congolense, T. vivax challenge and cross species-superchallenges, and related effects on health and productivity were assessed in N'Dama cattle. Twenty-five N'Dama bulls aged 3-4 years and previously primed with trypanosome infections through natural tsetse exposure over more than one year were used. The experimental herd was divided in five groups each composed of five randomly selected animals. Group 1 was challenged with T. congolense, Group 2 with T. vivax, Group 3 was inoculated with T. congolense followed by a cross-superchallenge with T. vivax, Group 4 was inoculated with T. vivax followed by T. congolense cross-superchallenge. Animals in Group 5 were used as controls. Both T. vivax and T. congolense cross-superchallenges were carried out on Day 14 subsequent to respective initial T. congolense and T. vivax inoculations. All challenges were performed by intradermal needle inoculation of stocks of trypanosome bloodstream forms. In challenged animals (Group 1 to 4), parasitaemia profiles and packed red cell volumes (PCV) were measured for four months. Weight changes were recorded monthly and daily weight gain (DWG) computed. All cattle challenged with T. congolense became parasitaemic. Conversely, one animal in Group 2 and two in Group 3 never displayed patent T. vivax parasitaemia. Both in single (Group 1), initial (Group 3) and cross-superchallenged (Group 4) cattle higher percentage of positive blood samples and higher parasitaemia level were obtained following T. congolense than T. vivax inocula (Group 2, 3 and 4) (P<0.04 or greater). Overall the pre-challenge period, PCV values and DWGs were nearly identical in the five groups. Conversely, over the post-challenge period, cattle singly, initially and cross-superinoculated with T. congolense (Group 1, 3 and 4) displayed lower PCV values and DWGs in comparison with both control animals (Group 5) and with singly T. vivax challenged cattle (Group 2) (P<0.05 or greater). No difference in mean PCV levels and DWGs was found between animals in Group 2 and cattle in Group 5. It was concluded that trypanotolerant N'Dama cattle suffered more from T. congolense and mixed T. congolensel T. vivax infections, while pure T. vivax infection did not produce appreciable negative effects on their health and productivity. Therefore, considering that tsetse and trypanosomosis control campaigns are costly and are justified only when derived economic benefits exceed those of control, and also that an ample mosaic of farming systems exists in West Africa, species-specific trypanosome prevalence and relative impact should be assessed in various cattle populations and breeds differing in trypanosome susceptibility before advising any intervention. Moreover, virulence and related effects of T. congolense and T. vivax endemic stocks on health and productivity in local cattle populations should also be estimated in order to counsel appropriate economic protection measures against trypanosmosis, i.e. vector control and/or strategic use of trypanocidal drugs.