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The sensitivity of PCR and serology in different Theileria parva epidemiological situations in Rwanda
No full textTheileria parva is the causative agent of a lethal tick-borne disease of cattle occurring in eastern, central and southern Africa. Variations in the sensitivity of the serological and molecular tests with seasonal vector occurrence and discrepancies between low PCR prevalence and high T. parva vector density are a setback to estimate true prevalences. Therefore, the objectives of the present studies were to evaluate (1) the sensitivity of three serological tests (IFAT, ELISA and SELISA) and one molecular test (PCR) in the diagnosis of chronic T. parva infections in four different agro-ecological zones of Rwanda and (2) the effect of tick challenge and animal's age on the sensitivity of PCR. Blood samples from 635 bovines were collected in four agro-ecological zones of Rwanda. All sera were screened using the IFAT, ELISA, SELISA and PCR. The binary results of the four diagnostic tests were introduced separately for each agro-ecological zone in a Bayesian model to estimate the prevalence of T. parva infections and the sensitivity of the four diagnostic tests. All test specificities were set to 100%. The estimated T. parva prevalence was much higher (83-85%) than estimations based on single diagnostic tests. The estimated sensitivity of serological tests was relatively constant and ranged from 57 to 75% in the various areas. The sensitivity of PCR showed more pronounced variations, ranging from 66% in the low T. parva transmission (high land) zones compared to 24% in the highly vector infested (low land) zones. Calves and adult cattle (n=194) were also sampled in regularly and irregularly dipped herds in the low land region. The apparent T. parva prevalence detected by PCR was significantly higher in calves than in adult cattle and in herds regularly treated with acaricides, while no significant differences were found with IFAT. The conditional probability that a sample was positive at PCR while it was positive at IFAT was significantly lower in adults. The implication of these findings in the use of diagnostic assays for epidemiological studies is discussed
Serological responses in porcine cysticercosis: link with the parasitological outcome of infection
No full textAn oral infection model with Taenia solium whole proglottids was used to study host-parasite relationships and the mechanisms underlying resistance to infection in pigs. In addition, an attempt was made to link the parasitological findings to serological data. Groups of six piglets aged 1, 3 and 5 months were infected and slaughtered 3 months p.i. Circulating antibody and antigen levels were monitored weekly. At autopsy total cyst counts were performed. Although the detailed carcass dissection at necropsy revealed a high variation in the number of cysts, the trend was that the number of viable cysts decreased with the age at which the animals were infected. The kinetics of the antigen levels throughout the course of the infection differed markedly between the three age groups of the experimental infection model. In the younger animals, a fast increase in titres of circulating antigen was observed in most animals, reaching a plateau as early as 2 weeks p.i. Besides its faster increase, antigen levels in pigs infected at younger ages also reached higher levels than in older animals and were associated with weaker antibody responses. Results also demonstrated that a relationship exists between the number of cysts and the titre of circulating antigen. This is promising in view of the development of an assay to quantify the progress of an active T. solium infection and would be a useful tool in epidemiological studies to assess the infection burden and the risk of transmission of the disease. The use of specific antibody-detection assays combined with circulating antigen detection could improve our understanding of this relationship
Investigations on the transmissibility of Trypanosoma congolense by the tsetse fly Glossina morsitans morsitans during its development in mammalian host
No full textExperiments were conducted to investigate the effect of the developmental stage of a monomorphic T. congolense IL1180 strain, in a vertebrate host, on its transmissibility by the tsetse fly Glossina morsitans morsitans Westwood (Diptera: Glossinidae). Batches of 160 male teneral tsetse flies were given a single bloodmeal on mice infected with this T. congolense strain 4, 5, 6, 7 or 10 days post-infection. The proportion of infected flies in each of those batches showed that the stage of development of the trypanosome does affect the proportion of flies that develop a mature or immature infection with immature and mature infection rates of flies infected on days 5 or 10 significantly higher. The proportion of infected flies was not affected by the parasitaemia at the moment of infection. Results show that tsetse flies can become infected at any phase of the development of the T. congolense IL 1180 strain but the ease with which trypanosomes develop in the fly depends on the phase in the parasite's development in the host. Those observations suggest that in analogy with the pleomorphic T. brucei s.l. adaptation of the monomorphic T. congolense to development in the fly may also determine the parasite's transmissibility. Moreover, the findings stress the importance of standardising experiments in which the vectorial capacity of tsetse flies is determined and compared
The role of hygienic bathing after defecation in the transmission of Schistosoma mansoni
No full textTransmission of Schistosoma mansoni depends on fecal eggs reaching water, but the way this happens is poorly understood. We studied the role of hygienic bathing after defecation in the contamination of water with S. mansoni eggs. Individuals in an endemic community in Northern Senegal (n=991) were examined for S. mansoni infection and a random sample (22%) was interviewed about stool disposal practices and hygienic behavior. We assessed the presence and viability of S. mansoni eggs adhering to the peri-anal region of 13 infected volunteers, by counting the miracidia in the water they had used for hygienic washing; for 10 of them (77%) miracidia were demonstrated. From the population infection distribution, average number of defecations per day, proportion of individuals bathing after defecation, and association between miracidial counts and infection intensity, we calculated a daily population miracidial output of approximately 30000 through hygienic bathing. For comparison, one complete stool reaching the water was calculated to yield approximately 2500 miracidia. Thus, 12 individuals in this population should defecate into the water every day to produce the same number of miracidia as through hygienic bathing. Our results suggest a major role of hygienic bathing after defecation in the transmission of S. mansoni
Risk factors associated with bovine tuberculosis in traditional cattle of the livestock/wildlife interface areas in the Kafue basin of Zambia
No full textWe conducted a cross-sectional study from August 2003 to February 2004 to identify risk factors for bovine tuberculosis (BTB) in the Kafue basin of Zambia. We investigated a total of 106 herds of cattle for presence of BTB using the comparative intradermal tuberculin test (CITT) while an interviewer-administered questionnaire was used to gather epidemiological data on herd structure, management and grazing strategies. BTB prevalence at herd level was estimated and possible risk factors were investigated using the multiple logistic regression model. The true herd level prevalence of BTB was estimated at 49.8% (95% CI: 37.9, 61.7%). The logistic regression model showed that cattle herd BTB status was highly associated with area and husbandry practices. When compared to Kazungula, cattle herds in Blue Lagoon were more likely to test positive for BTB when other factors such as management practices were controlled (OR = 10.5). In terms of grazing strategies, transhumant herds (TH) had higher odds (OR = 3.0) of being positive compared to sedentary herds (OR = 1.0). The results in this study provide preliminary information about potential risk factors that were found to be associated with BTB status in cattle
Evaluation of blood agar for susceptibility testing of Mycobacterium tuberculosis against first-line antituberculous drugs: results from two centers [letter]
No full text
The insecticide resistance status of malaria vectors in the Mekong region
No full textBackground: Knowledge on insecticide resistance in target species is a basic requirement to guide
insecticide use in malaria control programmes. Malaria transmission in the Mekong region is mainly
concentrated in forested areas along the country borders, so that decisions on insecticide use
should ideally be made at regional level. Consequently, cross-country monitoring of insecticide
resistance is indispensable to acquire comparable baseline data on insecticide resistance.
Methods: A network for the monitoring of insecticide resistance, MALVECASIA, was set up in the
Mekong region in order to assess the insecticide resistance status of the major malaria vectors in
Cambodia, Laos, Thailand, and Vietnam. From 2003 till 2005, bioassays were performed on adult
mosquitoes using the standard WHO susceptibility test with diagnostic concentrations of
permethrin 0.75% and DDT 4%. Additional tests were done with pyrethroid insecticides applied by
the different national malaria control programmes.
Results: Anopheles dirus s.s., the main vector in forested malaria foci, was susceptible to
permethrin. However, in central Vietnam, it showed possible resistance to type II pyrethroids. In
the Mekong delta, Anopheles epiroticus was highly resistant to all pyrethroid insecticides tested. It
was susceptible to DDT, except near Ho Chi Minh City where it showed possible DDT resistance.
In Vietnam, pyrethroid susceptible and tolerant Anopheles minimus s.l. populations were found,
whereas An. minimus s.l. from Cambodia, Laos and Thailand were susceptible. Only two An. minimus
s.l. populations showed DDT tolerance. Anopheles vagus was found resistant to DDT and to several
pyrethroids in Vietnam and Cambodia.
Conclusion: This is the first large scale, cross-country survey of insecticide resistance in Anopheles
species in the Mekong Region. A unique baseline data on insecticide resistance for the Mekong
region is now available, which enables the follow-up of trends in susceptibility status in the region
and which will serve as the basis for further resistance management. Large differences in insecticide
resistance status were observed among species and countries. In Vietnam, insecticide resistance
was mainly observed in low or transmission-free areas, hence an immediate change of malaria
vector control strategy is not required. Though, resistance management is important because the
risk of migration of mosquitoes carrying resistance genes from non-endemic to endemic areas.
Moreover, trends in resistance status should be carefully monitored and the impact of existing
vector control tools on resistant populations should be assessed
Molecular analysis of archived blood slides reveals an atypical human Trypanosoma infection
No full textIn 2003, a 10-month-old Ghanaian boy recovered from a Trypanosoma brucei infection, although the patient was not treated with antitrypanosomal drugs. Only T. brucei gambiense and T. brucei rhodesiense are able to infect humans, causing human African trypanosomiasis. The disease is considered 100% fatal if left untreated. The identity of the trypanosome was determined by DNA extraction from the archived stained blood slides followed by sequential application of polymerase chain reactions (PCRs) that are specific for the order, subgenus, species and subspecies, followed by genotyping with microsatellite PCR. Molecular analysis indicated that the parasites observed in the patient's blood in 2003 belong to the T. brucei subspecies brucei, which is normally not infectious to humans. Next to the clinical message, this article provides technical information to extract successfully DNA from archived blood slides for subsequent molecular analysis and to identify a trypanosome by taxon-specific PCRs and microsatellite genotyping
