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Biomedical subjects

L Oskam

Publications and source records attributed to L Oskam.

At least 19 recordsLinked to original sources

Direct detection of Staphylococcus aureus mRNA using a flow through microarray.

The direct detection of mRNAs from bacterial cultures on a DNA array without amplification and labelling would greatly extend the range of applications suitable for microarray analysis. Here we describe the direct detection of 23S rRNA and seven mRNA species from total Staphylococcus aureus RNA prepared using commercially available RNA purification columns followed by fluorescent detection on a flow through microarray. RNA hybridisation was detected using paired secondary labelled probes directly 5' and 3' to immobilised 60 mers. In this way, we were able to detect the effect of 30-min exposure to antimicrobials on mRNA levels within 3 h after column purification of total RNA without the need for enzymatic manipulation. Specifically the expression of mecA was confirmed in a highly resistant strain and induction of katA and ile-tRNA synthetase genes after exposure to mupirocin could be detected.

Humans↗

High prevalence of vasomotor reflex impairment in newly diagnosed leprosy patients.

BACKGROUND: Initial nerve damage in leprosy occurs in small myelinated and unmyelinated nerve fibers. Early detection of leprosy in the peripheral nervous system is challenging as extensive nerve damage may take place before clinical signs of leprosy become apparent. PATIENTS AND METHODS: In order to determine the prevalence of, and factors associated with, peripheral autonomic nerve dysfunction in newly diagnosed leprosy patients, 76 Brazilian patients were evaluated prior to treatment. Skin vasomotor reflex was tested by means of laser Doppler velocimetry. Blood perfusion and reflex vasoconstriction following an inspiratory gasp were registered on the second and fifth fingers. RESULTS: Vasomotor reflex was impaired in at least one finger in 33/76 (43%) patients. The fifth fingers were more frequently impaired and suffered more frequent bilateral alterations than the second fingers. Multivariate regression analysis showed that leprosy reaction (adjusted odds ratio = 8.11, 95% confidence interval: 1.4-48.2) was associated with overall impaired vasomotor reflex (average of the four fingers). In addition, palmar erythrocyanosis and an abnormal upper limb sensory score were associated with vasomotor reflex impairment in the second fingers, whereas anti-phenolic glycolipid-I antibodies, ulnar somatic neuropathy and a low finger skin temperature were associated with impairment in the fifth fingers. CONCLUSIONS: A high prevalence of peripheral autonomic dysfunction as measured by laser Doppler velocimetry was observed in newly diagnosed leprosy patients, which is clinically evident late in the disease. Autonomic nerve lesion was more frequent than somatic lesions and was strongly related to the immune-inflammatory reaction against M. leprae.

Adolescent↗

Risk factors for the development of clinical leprosy among contacts, and their relevance for targeted interventions.

Existing knowledge on risk factors for the development of clinical leprosy among contacts of known leprosy patients is reviewed with the aim to identify factors associated with leprosy among contacts that have potential for developing effective targeted interventions in leprosy control. Different definitions of 'contact' have been used and most studies on this subject were among so-called household members. Yet several studies indicate that contacts found in other places than the household are also at risk of developing leprosy. The type of leprosy and the bacterial index are the main patient-related factors involved in transmission, but also contacts of PB patients have a higher risk of contracting leprosy as compared to the general population. The most important contact-related factors are the closeness and intensity of the contact and inherited susceptibility, while the role of age and sex of the contacts is not clear. The role of socio-economic factors is also vague. The significance of immunological and molecular markers in relation to risk of transmitting or developing leprosy is not yet fully understood, but there is an indication that contacts who are sero-positive for anti-PGL-I antibodies are at increased risk of developing clinical leprosy. The presence of a BCG scar is likely to be related to a lower risk. Analogies with tuberculosis suggest that the 'stone-in-the-pond' approach to control may be applicable to leprosy too. Sputum smear negative tuberculosis patients are known to spread the bacteria to others. This analogy strengthens the suggestion that the contacts of paucibacillary leprosy cases should also be included in contact tracing and examination. It is concluded that targeted interventions should be aimed at close contacts of both MB and PB patients inside and outside the household, particularly when genetically related.

Adolescent↗

A study on transmission and a trial of chemoprophylaxis in contacts of leprosy patients: design, methodology and recruitment findings of COLEP.

In this article, we describe the design, methodology and recruitment findings of the COLEP study. The objectives of this study were to determine the effectiveness of chemoprophylaxis with a single dose of rifampicin in the prevention of leprosy among close contacts of leprosy patients, and to find characteristics of contact groups most at risk to develop clinical leprosy. These characteristics should be usable by routine leprosy control programmes. COLEP consists of a cluster randomized, double-blind and placebo-controlled trial, a cohort study to determine risk factors characterizing the sub-groups most at risk within the total contact group of a patient, and a cohort study using a reference group from the general population to determine the prevalence and incidence of leprosy in the total population of the study area. The follow-up period will be 4 years. A coding system was developed describing the physical and genetic distance of the contact person to the patient. This study in Bangladesh includes 1037 newly diagnosed and previously untreated leprosy patients and their 21,867 contacts. The prevalence of leprosy among contacts was 7.3 per 1000. A total of 21,708 contacts without signs and symptoms of clinical leprosy are included in a trial of chemoprophylaxis with single dose rifampicin, and randomized at contact group level in treatment and placebo arms. The results of this large field trial will become available in the years to come.

Adolescent↗

Simple and fast lateral flow test for classification of leprosy patients and identification of contacts with high risk of developing leprosy.

The interruption of leprosy transmission is one of the main challenges for leprosy control programs since no consistent evidence exists that transmission has been reduced after the introduction of multidrug therapy. Sources of infection are primarily people with high loads of bacteria with or without clinical signs of leprosy. The availability of a simple test system for the detection of antibodies to phenolic glycolipid-I (PGL-I) of Mycobacterium leprae to identify these individuals may be important in the prevention of transmission. We have developed a lateral flow assay, the ML Flow test, for the detection of antibodies to PGL-I which takes only 10 min to perform. An agreement of 91% was observed between enzyme-linked immunosorbent assay and our test; the agreement beyond chance (kappa value) was 0.77. We evaluated the use of whole blood by comparing 539 blood and serum samples from an area of high endemicity. The observed agreement was 85.9% (kappa = 0.70). Storage of the lateral flow test and the running buffer at 28 degrees C for up to 1 year did not influence the results of the assay. The sensitivity of the ML Flow test in correctly classifying MB patients was 97.4%. The specificity of the ML Flow test, based on the results of the control group, was 90.2%. The ML Flow test is a fast and easy-to-perform method for the detection of immunoglobulin M antibodies to PGL-I of M. leprae. It does not require any special equipment, and the highly stable reagents make the test robust and suitable for use in tropical countries.

Antibodies, Bacterial↗

Effect of secondary structure on single nucleotide polymorphism detection with a porous microarray matrix; implications for probe selection.

Oligonucleotide arrays capable of detecting single nucleotide polymorphisms (SNPs) from amplified nucleic acid have many applications. The expected SNP is usually placed approximately in the center of the probe to ensure the maximum shift in Tm between complementary and SNP sequences. Unfortunately, different short probes (< 30 bases) selected using widely accepted criteria do not perform consistently in this type of assay. Here we present a systematic study on the effect of secondary structure on the ability of oligonucleotide probes to detect an SNP, using real-time array monitoring of a porous microarray substrate that incorporates a novel intra-array mixing system. These results demonstrate that, although positioning of an SNP in the middle of the probe is highly destabilizing, the effect of stable secondary structure on the signal obtained is so dramatic that such probes may be very insensitive. Therefore, if the SNP flanking sequence contains significant secondary structure, then more sensitive probes with good specificity may be obtained by positioning the mutation towards one end of the probe.

Artifacts↗

Knowledge and use of prevention measures related to dengue in northern Thailand.

OBJECTIVE: To determine the frequency and determinants of knowledge of dengue infection in three sites in northern Thailand, and to compare prevention measures of people with and without knowledge of dengue. METHODS: In May 2001 we conducted an epidemiological survey among 1650 persons living in three areas in northern Thailand. Knowledge of dengue and the use of prevention measures were measured by means of a structured questionnaire. Differences in knowledge of dengue and the use of prevention measures between risk groups were calculated by chi-square test. Logistic regression was used to identify determinants of knowledge. RESULTS: Of the 1650 persons, 67% had knowledge of dengue. Fever (81%) and rash (77%) were the most frequently mentioned symptoms. Persons with knowledge of dengue reported a significantly higher use of prevention measures than persons without knowledge of dengue. In multivariate analyses, knowledge of dengue significantly differed by age, sex, occupation and site (P < 0.05). Younger people knew more about dengue than older persons: adjusted odds ratio (aOR) of 6.75 [95% confidence interval (CI): 4.32-10.6] for the 15-29 age group compared with people aged 60 and older. In comparison with farmers (reference group), knowledge of dengue was significantly higher among students (aOR: 10.6, 95% CI: 4.27-26.4), but lower among housewives or unemployed persons (aOR: 0.44, 95% CI: 0.31-0.64). CONCLUSION: The overall knowledge of dengue was high, but housewives, unemployed and old persons had relatively little knowledge of dengue. Therefore, these groups may need special attention in future dengue education programmes. Persons with knowledge of the disease more frequently reported the use of preventive measures, indicating the value of education programmes as a tool in dengue prevention.

Adolescent↗

Leishmania donovani: intraspecific polymorphisms of Sudanese isolates revealed by PCR-based analyses and DNA sequencing.

Four polymerase chain reaction (PCR)-based approaches were used to analyze diversity within 23 Sudanese isolates of Leishmania donovani. Methods compared were fingerprinting with single nonspecific primers, restriction analysis of the amplified ribosomal internal transcribed spacer (ITS) locus, single-stranded conformation polymorphism (SSCP), and sequencing of the ITS region. When PCR fingerprinting and restriction analysis of ITS were applied, highly similar fragment patterns were observed for all strains of L. donovani studied. The ITS1 locus gave five different SSCP profiles among the 23 Sudanese isolates, whereas the ITS2 locus was highly conserved with the exception of 1 isolate. Strains of L. donovani derived from other geographical areas were found to have different ITS2 patterns. SSCP analysis correlated well with results of DNA sequencing and confirmed that SSCP was able to detect genetic diversity at the level of a single nucleotide. SSCP had advantages over the other methods employed for investigation of sequence variation within the species L. donovani. There was no correlation between the form of clinical manifestation of the disease and the PCR fingerprinting, ITS-RFLP, or ITS-SSCP characteristics.

Animals↗

Dipstick assay to identify leprosy patients who have an increased risk of relapse.

Classification of leprosy patients into paucibacillary (PB) and multibacillary (MB) determines the duration of treatment; misclassification increases the risk of relapse because of insufficient treatment if an MB patient is classified as PB. We explored the possibility of using a simple dipstick assay based on the detection of antibodies to the Mycobacterium leprae-specific phenolic glycolipid-I (PGL-I) as a tool for classification of patients into PB and MB for treatment purposes. The sensitivity of the dipstick test for detection of MB patients was 85.1%, the specificity 77.7%. We found that of the 71 dipstick negative PB patients 25 (35.2%) were clinically cured at the end of treatment, compared with only two (9.5%) of the 21 dipstick positive PB patients. Of 170 patients in the study population, nine (5.3%) relapsed within the 5-year follow-up period. Seven were MB patients, all dipstick positive. Two PB patients relapsed, one was dipstick negative and one was dipstick positive. Dipstick positivity is a risk factor for the future development of relapses, especially in those groups of patients who had received a shorter-than-usual course of treatment and the dipstick can be used as an additional, simple tool for classification of patients and for identification of those patients who have an increased risk of relapse.

Antibodies, Bacterial↗

Simplified PCR detection method for nasal Mycobacterium leprae.

We report here a simplified method for the detection of nasal carriage of Mycobacterium leprae. DNA extracted from nasal swabs was analyzed by PCR, and M. leprae specific amplicons detected by means of a novel peptide-nucleic-acid-ELISA (PNA-ELISA) method. Parameters for the method were established using swabs taken from untreated lepromatous leprosy patients. We have developed this method to study nasal carriage in endemic populations. However, due to the sensitivity of PCR based techniques, we wished to assess the possibility of false positive samples arising in our method. We therefore examined samples taken from individuals in Norway, a country non-endemic for leprosy, using our technique. A total of 219 nasal swabs were collected and tested in our laboratory in London. All of these were found to be negative by our criteria. In order to corroborate our results, and also to assess the specificity of the method, a small number of these samples were randomly selected, and a known amount of M. leprae DNA added to them. All 219 samples were then retested using the same techniques under "double blind" conditions in our laboratory in India. All of the samples to which M. leprae DNA had been added were successfully identified by this method whereas all other swabs were negative. Taken together, these results suggest that the technique described here is simple, sensitive, and specific for use in large-scale epidemiological studies. This study, part of the larger MILEP 2 study, represents the first use of a PNA-PCR method for an epidemiological study of infection. The method using PNA-ELISA is significantly simpler and more rapid than gel based detection methods. The supply of laboratory consumables and overall detection procedure were simplified and standardized by use of PCR Ready-to-Go beads.

DNA, Bacterial↗

A survey on canine leishmaniasis in western Turkey by parasite, DNA and antibody detection assays.

Human visceral leishmaniasis (VL) caused by Leishmania infantum is found throughout the Mediterranean Region, including Turkey, where dogs are considered to be the main reservoir host for this parasite. In the district of Manisa, western Turkey, 37 human VL cases were reported from June 1993-August 1997. Twenty-four villages in this district were chosen for a survey of disease prevalence in dogs. The dogs, 490 in total, were examined using either the indirect immunofluoresence assay (IFAT) or direct agglutination test (DAT). Anti-Leishmania antibodies were found by at least one test in 5.3% (26/490) of the dogs. Infections were confirmed by parasitological examination of or polymerase chain reaction (PCR) on lymph node aspirates in 65% (13/20) and 76.4% (13/17) of the seropositive dogs tested, respectively. The confirmation rate was 85% by combining the results of PCR and microscopy. Our results demonstrate that canine VL is wide spread in western Turkey where human VL is endemic, and that serodiagnosis is a valuable tool for monitoring the infection.

Animals↗

Detection of Leishmania in immunocompromised patients using peripheral blood spots on filter paper and the polymerase chain reaction.

The aim of the present study was to investigate whether the polymerase chain reaction could be used to detect Leishmania infantum in peripheral blood spots of immunocompromised patients. Although visceral leishmaniasis in immunocompromised individuals is routinely diagnosed by direct microscopy or by culture of biopsy material, both methods have disadvantages. In order to evaluate an alternative method of diagnosis, blood spots were collected on filter paper from 24 immunocompromised individuals with visceral leishmaniasis diagnosed by bone marrow microscopy or culture. The samples were tested using the polymerase chain reaction. Leishmania DNA was detected in 15 of 20 patients who had not yet begun treatment for Leishmania infection and in two of four patients undergoing treatment. Using microscopy or culture, parasites were detected in 5 of 19 and 8 of 19 fresh blood samples, respectively. The results suggest that the polymerase chain reaction can be used with blood spots on filter paper as an initial screening method for immunocompromised patients suspected to have Leishmania infection.

Animals↗

Leishmaniasis in the Sudan: a literature review with emphasis on clinical aspects.

The literature on the leishmaniases in the Sudan is reviewed with an emphasis on clinical aspects and on literature related to the recent outbreaks in the south and east of the country. The numbers of cases of subclinical infection and post-kala azar dermal leishmaniasis in the recent outbreaks are remarkable. New diagnostic techniques have been introduced and evaluated, notably the direct agglutination test and polymerase chain reaction technology. The latter gives very promising results and further research into application of the technique is warranted. Treatment with pentavalent antimony is still satisfactory. The reservoir host has not been identified definitely.

Agglutination Tests↗

Detection and quantification of Plasmodium falciparum in blood samples using quantitative nucleic acid sequence-based amplification.

A quantitative nucleic acid sequence-based amplification (QT-NASBA) assay for the detection of Plasmodium parasites has been developed. Primers and probes were selected on the basis of the sequence of the small-subunit rRNA gene. Quantification was achieved by coamplification of the RNA in the sample with one modified in vitro RNA as a competitor in a single-tube NASBA reaction. Parasite densities ranging from 10 to 10(8) Plasmodium falciparum parasites per ml could be demonstrated and quantified in whole blood. This is approximately 1,000 times more sensitive than conventional microscopy analysis of thick blood smears. Comparison of the parasite densities obtained by microscopy and QT-NASBA with 120 blood samples from Kenyan patients with clinical malaria revealed that for 112 of 120 (93%) of the samples results were within a 1-log difference. QT-NASBA may be especially useful for the detection of low parasite levels in patients with early-stage malaria and for the monitoring of the efficacy of drug treatment.

Animals↗

Use of ML dipstick as a tool to classify leprosy patients.

Leprosy control services face the problem of leprosy patients being misclassified by the lack of or the poor quality of skinsmear examination services. Misclassification increases the risk of relapse due to insufficient treatment if a multibacillary (MB) patient is classified as paucibacillary (PB), thereby also prolonging the time that the patient is infectious. The World Health Organization (WHO) recommends at present an alternative classification based on the number of skin lesions. Its reliability, however, has been questioned. Our investigation sought to determine the usefulness of the ML Dipstick, a simple field assay to detect IgM antibodies to phenolic glycolipid-I of Mycobacterium leprae, for the classification of leprosy patients in addition to lesion count. In this study, 264 leprosy patients were investigated. Of 130 patients with a positive bacterial index (BI), 19 (14.6%) had less than 6 lesions and would have been classified as PB. Out of 134 patients with a negative BI, 26 (19.4%) had 6 or more lesions and would have been classified as MB patients if the lesion counting system would apply. Thus, the classification based on the number of lesions only was found to be 85% sensitive and 81% specific (using the BI as the gold standard) at detecting MB cases among the studied population. Sensitivity would have increased if patients would have been classified according to a combination of the number of lesions and the dipstick result. In that case patients are classified as MB when they are either dipstick positive (N = 16), have more than 6 lesions (N = 43), or both (N = 94). Patients negative for both dipstick and number of lesions would have been classified as PB (N = 111). The classification based on the number of lesions alone left 19 BI-positive cases classified as PB, while the combination method of the ML Dipstick and number of lesions left only 8 BI-positive cases classified as PB (5 borderline, 2 borderline lepromatous and 1 tuberculoid), thus preventing undertreatment. The combination method of the ML Dipstick and lesion counting was found to be 94% sensitive and 77% specific, which is an improvement of 9% (chi-squared test, p = 0.025) in sensitivity compared to lesion counting only. The results of this study indicate that testing all patients initially classified by lesion counting as PB (48% in our study population) with the dipstick can significantly contribute to improved classification of leprosy patients for treatment purposes.

Antibodies, Bacterial↗

Congenital transmission of visceral leishmaniasis (Kala Azar) from an asymptomatic mother to her child.

In this article, we report the case of a 16-month-old German boy who was admitted to the Children's Hospital of Stuttgart with a 4-week history of intermittent fever, decreased appetite, weakness, fatigue, and difficulty sleeping. He was healthy at birth and remained so for the first 15 months of his life. On admission, physical examination showed enlarged cervical, axillary, and inguinal lymph nodes, as well as hepatosplenomegaly. Laboratory data revealed pancytopenia, elevated liver function tests, and hypergammaglobulinemia. Blood, stool, and urine culture results were negative. Viral infections and rheumatologic and autoimmune disorders were ruled out, but a positive titer for Leishmania antibodies was noted. In a liver and bone marrow biopsy, the amastigote form of the parasite could not be seen in cells. The promastigote form of Leishmania was found and the diagnosis of visceral leishmaniasis was made by combining the cultures of both the liver and the bone marrow biopsy material in 5 mL 0.9% saline on brain heart infusion agar, supplemented with defibrinated rabbit blood and incubated at 25 to 26 degrees C for 5 days. The parasite was identified by Southern blot analysis as Leishmania infantum. Specific therapy with the antimonial compound sodium stibogluconate with a dose of 20 mg/kg body weight was begun immediately. Within 4 days, the patient became afebrile. The side effects of treatment, including erosive gastritis, cholelithiasis, worsening hepatosplenomegaly, elevation of liver enzymes, pancreatitis, and electrocardiogram abnormalities, necessitated the discontinuation of treatment after 17 days. On discharge 4 weeks later, the patient was stabilized and afebrile with a normal spleen, normal complete blood count, normal gammaglobulins, and decreasing antibody titers to Leishmania. During the next 24 months, the patient experienced intermittent episodes of abdominal pain, decreased appetite, recurrent arthralgia, and myalgia. But at his last examination in January 1998, he was well; all symptoms mentioned above had disappeared. Because the child had never left Germany, nonvector transmission was suspected and household contacts were examined. His mother was the only one who had a positive antibody titer against Leishmania donovani complex. She had traveled several times to endemic Mediterranean areas (Portugal, Malta, and Corse) before giving birth to the boy. But she had never been symptomatic for visceral leishmaniasis. Her bone marrow, spleen, and liver biopsy results were within normal limits. Culture results and polymerase chain reaction of this material were negative. A Montenegro skin test result was positive, indicating a previous infection with Leishmania. Western blot analysis showed specific recognition by maternal antibodies of antigens of Leishmania cultured from the boy's tissue. Visceral leishmaniasis is endemic to several tropical and subtropical countries, but also to the Mediterranean region. It is transmitted by the sand fly (Phlebotomus, Lutzomyia). Occasional nonvector transmissions also have been reported through blood transfusions, sexual intercourse, organ transplants, excrements of dogs, and sporadically outside endemic areas. Only 8 cases of congenital acquired disease have been described before 1995, when our case occurred. In our patient, additional evaluation showed that the asymptomatic mother must have had a subclinical infection with Leishmania that was reactivated by pregnancy, and then congenitally transmitted to the child. Visceral leishmaniasis has to be considered in children with fever, pancytopenia, and splenomegaly, even if the child has not been to an endemic area and even if there is no evidence of the disease in his environment, because leishmaniasis can be transmitted congenitally from an asymptomatic mother to her child.

Animals↗

Use of PCR for diagnosis of post-kala-azar dermal leishmaniasis.

Microscopy and PCR were compared for use in the diagnosis of post-kala-azar dermal leishmaniasis (PKDL) in 63 patients. Aspirates of lymph nodes (samples from 52 patients), skin (23 samples), and bone marrow (18 samples) were used. For 11 patients lymph node aspiration could be repeated 6 months after they recovered from PKDL. During active PKDL, PCR was positive for 42 of 52 (80.8%) lymph node aspirates and 19 of 23 (82.7%) skin aspirates, whereas microscopy was positive for only 9 of 52 (17.3%) lymph node aspirates and 7 of 23 (30.4%) skin aspirates. PCR was always positive when parasites were seen by microscopy. When the results obtained with lymph node and skin aspirates from the same patient (n = 16) were compared, there was complete agreement. Bone marrow samples were negative by microscopy and PCR for 16 patients and positive by both methods for 1 patient; for one sample only the PCR was positive. PCR confirmed the co-occurrence of visceral leishmaniasis and PKDL in one patient and confirmed the suspicion of this co-occurrence in the other patient. After recovery, no parasites were found by microscopy, but 2 of 11 (18.2%) samples were still positive by PCR. Thirty negative controls were all found to be PCR negative, and 15 positive controls were all PCR positive. Cross-reactions with Mycobacterium leprae could be ruled out. In conclusion, PCR with inguinal lymph node or skin aspirates is suitable for confirming the clinical diagnosis of PKDL. In some patients, lymph node aspirates are probably preferred because aspiration of material from the skin may leave scars.

Animals↗

Detection of Onchocerca volvulus DNA in pools of wild-caught Simulium ochraceum by use of the polymerase chain reaction.

The presence of Onchocerca volvulus DNA in experimentally infected flies can now be detected by use of the PCR, so that, for example, one infected Simulium damnosum can be detected in a pool of 100 uninfected flies or one S. ochraceum can be detected in pools of 20-40. As this PCR technique is specific for O. volvulus, the results are not confounded by the presence of other, unimportant, Onchocerca species, and the technique could replace time-consuming, manual dissection of flies. In 1996 and 1997, pools of 16-21 Simulium ochraceum were tested by the PCR technique. These flies had been collected biting man, between 1992 and 1994, from two hyperendemic coffee estates (fincas) in Guatemala, and stored in commercial (95%) ethanol. Collections at finca Buena Vista (869 flies in 52 pools) were made 1-2 weeks and 46 weeks after 45% of eligible subjects had been treated with ivermectin for the first time. At finca El Brote, collections (360 flies in 18 pools) were made 13 weeks before and 7 weeks after 97% of eligible subjects had received their first treatment. DNA was easily recovered from simuliids that had been stored in ethanol for up to 4 years. Of the nine pools of flies with visible blood collected at Buena Vista, each of 20 flies, eight tested positive for O. volvulus DNA. In flies without blood, 13 of 22 pools collected at Buena Vista just after treatment tested positive, whereas there were 14 positives in 22 pools taken 46 weeks later (P > 0.05). At El Brote, nine of 10 pre-treatment pools were positive, compared with three of eight taken 7 weeks post-treatment (P = 0.04), indicating that the treatments in this finca had reduced infection in the vector, and possibly transmission, by about 60%. A sub-sample of Buena Vista flies was divided into 19 sets of three separate sub-pools containing heads, thoraces and abdomens. Three pools of heads alone were positive, and had corresponding pools of positive abdomens. Three positive pools of thoraces had negative corresponding pools of heads and abdomens. These results show that PCR can be used to determine the prevalence of O. volvulus DNA in wild-caught S. ochraceum. As the infection rates observed were higher than expected from dissections reported by other workers, PCR-determined rates may not be directly comparable with traditional parameters based on the dissection of flies to reveal O. volvulus larvae.

Animals↗