The responses of a tropical breed of domestic rabbit, Oryctolagus cuniculus, to experimental infection with Trichostrongylus colubriformis.

Clinical, parasitological and pathological responses of a tropical out-bred domestic rabbit to experimental Trichostrongylus colubriformis infection were used to evaluate its suitability as a laboratory host and model for studying the host-parasite relationships of T. colubriformis. In the first experiment, three groups each of 16, predominantly juvenile male, 8- to 10-week-old rabbits were given a single pulse infection with 500, 5000 or 25000 infective larvae (L3) of T. colubriformis, to represent low, medium and high levels of infection, respectively. A fourth group of 16 rabbits of similar age formed the uninfected controls. In the second experiment, two groups of 10 juvenile (8- to 10-week-old) and 10 adult (8- to 10-month-old) rabbits were similarly infected with 20000 L3, with appropriate naive controls. Prepatency was 14 and 16 days and peak faecal egg counts occurred on days 24 and 20 after infection in young and adult rabbits respectively. Peak worm counts occurred on day 14 in both age groups and at all levels of infection. Subsequently, parasite burdens declined in a highly significantly dose- and age-dependent manner. At low and moderate levels of infection, approximately 83-98% of worms were recovered from the first 60 cm of the small intestine. Worm fecundity was also significantly influenced by host age and larval dose. Host age also had a significant effect on worm length. Infections with T. colubriformis were associated with a highly significant loss of body weight, accompanied by anorexia, diarrhoea and 25% mortality at high dose levels during the patent period of infection. There were no significant changes in packed cell volume and eosinophil counts at all ages and levels of infection but significant lymphocytosis occurred at the high dose level between days 7 and 21. Parasite-specific serum IgG responses were not related to worm burden. Overall, data showed that this miniature, docile and relatively inexpensive breed of rabbit is a potentially valuable laboratory host for studying T. colubriformis infections. The larval dose, duration of infection and host age were major determinants of host responsiveness to primary infections in this rabbit genotype.

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.

Acute dermatitis caused by Amblyomma variegatum larvae on chickens.

Acute dermatitis caused by Amblyomma variegatum larvae infestation was observed in adult local Nigerian chickens. Skin lesions containing numerous A. variegatum larvae were observed on gross examination. Histopathology showed skin haemorrhages, larvae, necrosis and infiltration of eosinophils. It was suspected that the free range life of the birds could have predisposed them to the infestation.

Effects of the timing of antigen stimulation on parasitaemia profile and subsequent immunodepression in an experimentally induced Trypanosoma brucei infection.

The influence of administering sheep red cells (SRC) as antigens, either after or before a trypanosome challenge, on parasitaemia profile and antibody response was assessed in albino Wistar rats. High levels of parasitaemia associated with significantly depressed antibody response and packed cell volume (PCV) values were observed when trypanosome challenge preceded antigen stimulation. In contrast, a clear delay in the onset and development of parasitaemia occurred when antigen priming preceded trypanosome challenge. At the beginning, PCV values and antibody response to the antigen were in the range of levels found in control rats. However, as infection progressed, parasitaemia rose and significant immunological hyporesponsiveness developed which at least reached levels found in rats that had received trypanosome challenge prior to antigen stimulation. These findings should be taken into consideration when evaluating serological tests used for assessing responses to specific vaccinations, or for the diagnosis of infections based on rising antibody titres in the host.

Seasonal changes in the prevalence of Haemonchus and Trichostrongylus hypobiotic larvae in tracer goats in Malaysia.

An investigation into the seasonal changes in the population structure of Haemonchus and Trichostrongylus in tracer goats was conducted over 12 months at Serdang, an area in southern West Malaysia with year-round tropical rainfall. Successive groups of parasite-free tracer goats were grazed for a month alongside naturally infected adult goats and necropsied for worm counts 14 days after their removal from pasture. No hypobiotic larvae of Trichostrongylus were recovered. Hypobiotic larvae of Haemonchus were evident during each month of the year but accounted for only a very small proportion of the total Haemonchus burden. Very low levels were encountered from December through to June. Comparatively higher levels of hypobiosis were observed thereafter with a peak of 7.4% in September. The factors responsible for hypobiosis were not clearly defined but the phenomenon was associated with increasing levels of soil moisture storage. Host resistance, adult worm population of tracers and population of ingested L3 were ruled out as possible inducing factors.