Henk L Smits

Royal Tropical Institute, Amsterdamo, North Holland, Netherlands

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Publications (105)323.87 Total impact

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    ABSTRACT: Background: Human brucellosis is a preventable zoonoses that may become persistent, causing, if left untreated, severe localized disease. Occupational exposure to infected animals or animal products and consumption of fresh contaminated dairy are main risk factors. Methods: One hundred farmworkers employed at two cattle farms one in Khartoum North and one in Omdurman were screened for the presence of specific antibodies and seropositive workers were invited to donate a blood sample for blood culture. Molecular typing was used to characterize Brucella isolates. Results: Ten percent of farmworkers tested seropositive and while Brucella melitensis biovar 1 was isolated from the blood of three individuals, an isolate identical to the B. abortus S19 vaccine strain was isolated from a fourth person. All four bacteremic individuals were employed as milkers and did not have obvious disease. Conclusions: The isolation of the highly infectious pathogen B. melitensis from seropositive workers is consistent with the notion that the pathogen may persist in the blood without causing overt disease. While vaccination with strain S19 is essential for the control of bovine brucellosis the vaccine strain may be transmitted to the human population and protective measures remain important to prevent exposure also in view of the presence of B. melitensis. To create awareness for this potentially severe disease more information on the prevalence of the pathogen in different risk groups and in livestock in the Sudan is needed.
    PLoS ONE 05/2015; 10(5):e0123374. DOI:10.1371/journal.pone.0123374 · 3.23 Impact Factor
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    ABSTRACT: Brucellosis is a major cause of infertility and reproductive failure in livestock. While cattle in the Eastern Indonesian archipelago suffers from reproductive problems information on bovine brucellosis in the region is fragmentary. The control of brucellosis requires a major and prolonged effort and confirmation of the infection by isolation with detailed knowledge of the spread of the infection is essential when planning a control program. Serological investigation of Brucella infection in beef cattle tended under extensive farming conditions revealed a high seroprevalence (19.3%; 95%CI, 17--22) in the compliment fixation tests. The results of a rapid and simple field test correlated well with the Rose Bengal test (kappa, 0.917) and indicated an acceptable sensitivity (87.5%) and specificity (98.1%) compared with the complement fixation test. Reproductive failure was reported for 39.0% of the cows with a loss of calves due to abortion or early death amounting to 19.3%. Past reproductive failure did not, however, correlate with seropositivity in the complement fixation test (RP = 1.21; P = 0.847). B. abortus biovar 1 was freshly isolated from the hygromas of two cows and together with thirty banked isolates collected since 1990 from different parts of Sulawesi and Timor eight related genotypes could be distinguished with one genotype being identical to that of an isolate (BfR91) from Switzerland. The Indonesian genotypes formed together with BfR91 and one African and one North American isolate a distinct branch on the B. abortus biovar 1 dendogram. Bovine brucellosis appears to be widespread in the Eastern Indonesian archipelago and calls for urgent intervention. The fresh isolation of the pathogen together with the observed high seroprevalence demonstrates the presence and frequent exposure of cattle in the area to the pathogen. The application of a rapid and simple field test for brucellosis could be very useful for the quick screening of cattle at the pen side.
    BMC Veterinary Research 11/2013; 9(1):233. DOI:10.1186/1746-6148-9-233 · 1.78 Impact Factor
  • H L Smits
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    ABSTRACT: The traditional lifestyle and beliefs of pastoralists and small-scale farmers with confined livestock, together with certain farming environments, create favourable conditions for the spread and transmission of brucellosis. The risks associated with these practices are difficult to control because of a lack of alternatives and simple and/or affordable solutions. Brucellosis affects the health and productivity of livestock as well as that of their owners and caretakers and can have a deep economic impact. The control of brucellosis is likely to be cost effective. Good quantitative information on brucellosis in livestock and the human population is essential for demonstrating the benefits of intervention. Effective vaccines for the control of brucellosis in cattle and small ruminants are available and cheap, and in high-risk areas there is an urgent need to start large-scale vaccination programmes. Risks for the spread and transmission of brucellosis, such as the migration of herds with frequent contacts with other herds at common feeding grounds and near water sources, are inherent in the way of life of pastoralists. Such risks may need to be accepted when developing a control programme. Thus, the control of brucellosis by vaccination is expected to be more effective for confined livestock. Essential to the success of mass vaccination in controlling brucellosis is achieving a high degree of protection of adult livestock in a very short period and vaccinating young stock before natural infection can occur. To reduce the risk of transmission of infection from neighbouring areas where animals are not vaccinated, a region-wide approach is important. Because shepherds and farmers may have very little knowledge of infectious diseases and the consequences of infection, providing disease information and education is important to help them understand the need for control measures. Public health services can also assist in encouraging acceptance of control programmes in livestock by creating awareness of brucellosis as a human disease. To reduce costs, brucellosis control programmes can be combined with other veterinary or public health activities or interventions. An up-to-date livestock census and an effective surveillance system are crucial for the control of brucellosis, as the disease may quickly re-emerge from remaining foci of infection. Although test and slaughter may be an option for the management of remaining or re-emerging foci of infection, such a strategy is frequently not an option because of the cost.
    Revue scientifique et technique (International Office of Epizootics) 04/2013; 32(1):219-28. · 0.91 Impact Factor
  • Henk L Smits
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    ABSTRACT: Evaluation of: Siba V, Horwood PF, Vanuga K et al. Evaluation of serological diagnostic tests for typhoid fever in Papua New Guinea using a composite reference standard. Clin. Vaccine Immunol. 19(11), 1833-1837 (2012). The study under review evaluated serological tests for typhoid fever against PCR as a reference test. While laboratory testing is essential for the confirmation of this severe disease, the low bacterial load and the low level of specific antibodies in the blood of typhoid patients combined with its acute character make interpretation of laboratory testing cumbersome. Validation of an index test requires good understanding of the diagnostic performance and assay characteristics of the reference test, and criteria and principles for study design and reporting outlined by the Quality Assessment of Diagnostic Accuracy Studies and the Standards for Reporting Studies of Diagnostic Accuracy should be followed. Described PCR assays for typhoid fever have not been validated against bone marrow culture, the gold standard, and their diagnostic utility remains to be established.
    Expert Review of Molecular Diagnostics 03/2013; 13(2):147-9. DOI:10.1586/erm.12.145 · 3.52 Impact Factor
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    ABSTRACT: Brucella melitensis is highly infectious for humans and can be transmitted to humans in a number of epidemiological contexts. Within the context of an ongoing brucellosis surveillance project, an outbreak at a Peruvian police officer cafeteria was discovered, which led to active surveillance (serology, blood culture) for additional cases among 49 police officers who had also eaten there. The cohort was followed up to 18 months regardless of treatment or symptoms. Active surveillance estimated the attack rate at 26.5% (13 of 49). Blood cultures from four cases were positive; these isolates were indistinguishable using multiple locus variable number tandem repeat analysis. This investigation indicates the importance of case tracking and active surveillance for brucellosis in the context of potential common source exposure. These results provide rationale for public health investigations of brucellosis index cases including the bioterrorism-related dissemination of Brucella.
    The American journal of tropical medicine and hygiene 02/2013; 88(3). DOI:10.4269/ajtmh.12-0606 · 2.70 Impact Factor
  • Henk L Smits
    01/2012; 170(4):97-8. DOI:10.1136/vr.e666
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    ABSTRACT: Nigeria is the largest cattle-rearing nation in Africa with most animals kept under traditional husbandry practices. While bovine brucellosis does not receive much attention, a relatively high seroprevalence is found in samples submitted for laboratory testing. The aim of the study was to provide serological evidence of brucellosis in cattle from some of the main cattle-rearing states of the country and to validate a simple and rapid field test for the serodiagnosis of bovine brucellosis. Serum samples collected in various states of Nigeria from cattle because of suspicion of brucellosis were investigated in the Rose Bengal plate test, and results were compared with a newly developed rapid field test for the detection of Brucella-specific antibodies. Serological evidence for the presence of brucellosis in cattle was obtained for all states included in the study and a high herd prevalence was observed. The seroprevalence was also high among trade and slaughter animals. Results of a rapid field test for the serodiagnosis of bovine brucellosis correlated well with the Rose Bengal plate test (agreement, 95.7%; kappa value, 0.80). The results indicate that bovine brucellosis is an important veterinarian problem in Nigeria. The easy-to-use and robust field test is most promising for field-based surveillance as it provides an immediate result allowing the prompt instigation of control measures.
    Tropical Animal Health and Production 11/2011; 44(2):253-8. DOI:10.1007/s11250-011-0011-2 · 0.82 Impact Factor
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    ABSTRACT: Brucellosis is a major public health problem in Egypt. The Brucella IgM/IgG lateral flow assay was developed as a point-of-care test for the diagnosis of human brucellosis. The aim of this study was to assess the diagnostic value of the lateral flow assay for use in Egypt. Fifty samples of patients who presented with clinical suspicion of brucellosis over a one-year period were collected. All samples were subjected to the Brucella IgM/IgG lateral flow assay, serum agglutination test (SAT), rose bengal RB Test (RB), 2- mercapteoethanol (2-ME), culture and PCR. SAT, 2- ME, culture and PCR were retested after the end of the treatment. Culture and SAT confirmed the diagnosis of brucellosis in twenty patients. While 90% of the samples were positive by SAT, only 30% and 85% were positive by culture and PCR respectively. The sensitivity of the lateral flow assay calculated for the Brucella IgM/IgG was 95% and specificity was 97%. These data show that the lateral flow assay is more suitable for diagnosis of brucellosis in Egypt than culture and SAT. Application of the PCR on serum samples collected during follow-up revealed that the DNA of the pathogen was yet not completely cleared almost 60 days after the start of treatment with doxycycline and ciprofloxacin.
    The Journal of Infection in Developing Countries 11/2011; 5(11):786-91. DOI:10.3855/jidc.1538 · 1.14 Impact Factor
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    ABSTRACT: Multi-locus variable-number tandem repeat analysis differentiated 297 Salmonella enterica serovar Typhi blood culture isolates from Makassar in 76 genotypes and a single unique S. Typhi genotype was isolated from the cholecystectomy specimens of four patients with cholelithiasis. The high diversity in S. Typhi genotypes circulating in Makassar indicates that the number of carriers could be very large, which may complicate disease prevention and control.
    PLoS ONE 09/2011; 6(9):e24983. DOI:10.1371/journal.pone.0024983 · 3.23 Impact Factor
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    ABSTRACT: There is an urgent need for affordable point-of-care diagnostics for the differentiation of febrile illnesses and the confirmation of typhoid in endemic countries. Blood samples were collected from febrile patients with clinical suspicion of typhoid and screened for typhoid fever using the Widal and Typhi Dri Dot tests, while stool and blood samples were screened for Salmonella Typhi using the culture method as well as PCR as a confirmatory test. A high proportion of febrile patients from Lagos with clinical suspicion of typhoid fever reacted positively in a simple and rapid latex agglutination assay for typhoid fever, indicating that this illness is a common and presumably under-diagnosed health problem in this metropolis. Seropositivity was 19.2% in the rapid test compared with 22.9% in the classical Widal test. The confirmation of typhoid in these seropositive patients appeared cumbersome because of negative blood cultures and low DNA yield in molecular testing. A review of the literature revealed that in Nigeria seroprevalence rates can be high in the normal population and that pathogens other than S. Typhi are often isolated from the blood of seropositive febrile patients. The simplicity and the relatively high specificity (97.8%) of the rapid test as determined in a study performed in Indonesia calls for a further validation of this promising test for use in Africa.
    The Journal of Infection in Developing Countries 07/2011; 5(7):520-6. DOI:10.3855/jidc.1836 · 1.14 Impact Factor
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    ABSTRACT: Brucella melitensis biovar 1 was isolated from bovine milk samples from a herd in central Kenya, and Brucella abortus biovar 3 was isolated from aborted fetus materials and vaginal discharge fluids from cattle in central and eastern provinces of Kenya. All infections including those with B. melitensis were in cattle with reproductive problems kept in mixed herds indicating that cross infection occurs from small ruminants. Multiple-locus variable-number tandem repeat analysis genotyping revealed a close molecular homology of the B. melitensis isolates with an isolate from Israel and a close homology of the B. abortus isolates with an isolate from Uganda indicating that these genotypes have a wide geographic distribution. Infection of cattle with B. melitensis may complicate the control of brucellosis in this country.
    Tropical Animal Health and Production 06/2011; 44(1):17-20. DOI:10.1007/s11250-011-9899-9 · 0.82 Impact Factor
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    ABSTRACT: Laboratory confirmation of typhoid fever is essential for appropriate medical treatment. Blood culture is a standard test for diagnosis of typhoid fever, but well-equipped diagnostic facilities to perform culture are seldom available in endemic areas. We retrospectively compared 2 diagnostic field tests, a latex agglutination Dri-Dot assay and an IgM Lateral Flow assay, to blood culture, in patients with clinically diagnosed typhoid fever. Sensitivity of the Dri-Dot was 71.4%, and specificity was 86.3% for samples collected at time of first diagnosis. Sensitivity and specificity of IgM Lateral Flow were 80% and 71.4%, respectively. A major limitation of these serologic tests is the limited sensitivity at the early stage of the disease. Performing both tests in parallel increased sensitivity to 84.3%, but decreased specificity to 70.5%. There was a trend towards improved diagnostic performance using either assay over a longer duration of illness. These rapid, point-of-care assays for typhoid fever provide easy-to-interpret results in typhoid-endemic countries and may be most useful in patients presenting 1 week after symptom onset.
    Diagnostic microbiology and infectious disease 06/2011; 70(4):435-41. DOI:10.1016/j.diagmicrobio.2011.03.020 · 2.46 Impact Factor
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    Veterinary Microbiology 05/2011; 150(1-2):211-3. DOI:10.1016/j.vetmic.2011.01.015 · 2.51 Impact Factor
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    ABSTRACT: Typhoid fever was confirmed by positive blood culture in 5 (3.7%) of 134 febrile children hospitalized in Cambodia. Typhoid was suspected in an additional 25 (18.7 %) blood culture-negative children based on: a positive immunoglobulin M lateral flow assay (IgMFA) (16); a positive polymerase chain reaction (PCR) for Salmonella typhi (2); or clinical assessment (7). The specificity of the IgMFA and PCR assays requires further study. © The Author [2011]. Published by Oxford University Press. All rights reserved.
    Journal of Tropical Pediatrics 04/2011; 58(1):68-70. DOI:10.1093/tropej/fmr032 · 1.26 Impact Factor
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    Mochammad Hatta · Andi R Sultan · Rob Pastoor · Henk L Smits
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    ABSTRACT: Phase variation is a property unique of some Salmonella enterica serovar Typhi strains from Indonesia. Salmonella Typhi isolates from Indonesia have been described that in addition to the phase 1 Hd flagellin gene contain a second flagellin gene named z66. S. Typhi isolates from Indonesia with a mutant Hd gene named Hj have also been described. Here, we have identified another flagellin gene of S. Typhi, named Ind, showing a closest homology with the flagellin gene of Serratia marcescens. The Ind gene was detected in 21.8% of the S. Typhi isolates from the East Indonesian archipelago, all of which contained the Hd gene. The Hj gene was not detected. The z66 gene was present in 15.4% of the isolates. The presence of these "foreign" flagellin genes could be associated with an increased risk for developing severe disease.
    The American journal of tropical medicine and hygiene 03/2011; 84(3):429-34. DOI:10.4269/ajtmh.2011.10-0605 · 2.70 Impact Factor
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    ABSTRACT: Background: Micronutrients such as zinc (Zn) and copper (Cu) have a modulatory effect on immune system. Altered serum concentrations of these nutrients have been described in patients with specific disease conditions. The aim of this study was to evaluate serum Zn and Cu level alterations in patients with brucellosis in comparison with healthy individuals. Patients and methods: Serum Zn and Cu level of 43 patients with brucellosis (34 men and 9 women) were compared with 43 matched healthy controls. Serum micronutrient concentrations were measured by automatic absorptive spectrophotometry. Results: Mean serum Cu concentration was significantly higher in subjects with brucellosis when compared with age-matched healthy controls (p<0.05). Mean serum Zn level was decreased in female patients compared with controls (p<0.05), however, there was no significant difference between male patients and controls. Conclusion: Serum Zn and Cu concentrations may alter in patients with brucellosis during the period of infection. Further studies are needed to determine whether these micronutrients have an effect on disease severity and outcome. Measuring serum Cu level may be suggested as a complementary screening tool for brucellosis.
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    ABSTRACT: Serum samples from all patients with culture-confirmed brucellosis including those with chronic disease from Kazakhstan tested positive in the serum agglutination test for titers > or = 1:25 and reacted in the Brucella immunoglobulin M/immunoglobulin G lateral flow assay (LFA) confirming the high sensitivity of these assays. The strong reactivity in the LFA observed for the majority (92.1%) of the samples from the patients with culture-confirmed brucellosis together with the user-friendliness of the assay procedure makes the LFA ideal for the confirmation of brucellosis in endemic areas in Kazakhstan. The Rose Bengal test lacked sensitivity in particular for patients with chronic brucellosis therefore limiting its value as a quick screening assay. The study emphasizes the importance of the LFA as a useful, rapid, and easy-to-perform tool in the diagnostic testing of brucellosis.
    Diagnostic microbiology and infectious disease 10/2009; 65(1):14-20. DOI:10.1016/j.diagmicrobio.2009.05.002 · 2.46 Impact Factor
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    ABSTRACT: The multiple-locus variable-number repeat analysis of 90 human Brucella melitensis isolates from a large urban area in central Peru revealed variations at 4 (Bruce07, Bruce09, Bruce18, and Bruce42) out of 16 loci investigated, of which 1 (Bruce42) also is used for species identification. Ten genotypes were identified, separated by the number of Bruce42 repeats into two groups that may have distinct phenotypic characteristics. Whereas genotypes with five or six Bruce42 repeats were cultured mainly from adult patients, genotypes with three Bruce42 repeats were isolated from children and young adolescents as well as from adults. In addition, the isolates with three Bruce42 repeats were obtained more often from patients with splenomegaly (P = 0.02) or hepatomegaly (P = 0.006). An annual variation in the diversity of genotypes was observed, possibly reflecting changes in sources of fresh dairy products, supply routes to city shops and markets, and the movement of infected dairy goat herds.
    Journal of clinical microbiology 09/2009; 47(10):3147-55. DOI:10.1128/JCM.00900-09 · 3.99 Impact Factor
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    ABSTRACT: The lysis centrifugation technique is preferred for culturing Brucella spp. at all stages of brucellosis because it yields 25% more positive results and on average provides results 10 days earlier than the Ruiz-Castaneda method. This lysis method is inexpensive and easier to use and may be used in laboratories with limited expertise or equipment if all safety precautions are taken.
    The American journal of tropical medicine and hygiene 05/2009; 80(4):625-7. · 2.70 Impact Factor
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    Henk L Smits
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    ABSTRACT: The prospects for the control of neglected tropical diseases, including soil-transmitted helminthiasis, shistosomiasis, lymphatic filariasis, onchocerciasis and trachoma, through mass drug administration, are exemplified by the elimination of the trachoma as a public-health problem in Morocco. In spite of this and other striking successes, mass drug administration programs are faced with major challenges resulting from suboptimal coverage and lack of efficacy. At current suboptimal coverage rates, programs may need prolongation for an extended period, increasing costs and undermining sustainability. Community participation through health education and information appears to be crucial to improve coverage and to achieve sustainability. Implementation of complementary measures, such as vector control, improved hygiene and environmental sanitation, are important to further control transmission and to prevent re-emergence of the infection and, again, may only be achieved effectively through community-based initiatives. To reduce costs and to relieve pressure on the health system, combining neglected tropical disease programs in areas where diseases coexist and integration with existing control programs for malaria, tuberculosis and HIV/AIDS is advocated. The risk of developing drug resistance is of particular concern in view of the lack of alternative drugs, and reduced treatment efficacy due to emerging resistance is evident for the soil-transmitted helminths and onchocerciasis. Given the risk for the development of drug resistance and the need for a high degree of participation, close attention should be paid to the monitoring of the coverage and efficacy of the different program components.
    Expert Review of Anti-infective Therapy 03/2009; 7(1):37-56. DOI:10.1586/14787210.7.1.37 · 3.46 Impact Factor

Publication Stats

3k Citations
323.87 Total Impact Points


  • 1995–2013
    • Royal Tropical Institute
      • Department of Biomedical Research
      Amsterdamo, North Holland, Netherlands
  • 2009
    • Bundesinstitut für Risikobewertung
      Berlín, Berlin, Germany
  • 2008
    • Universidad Nacional Daniel Alcides Carrión, Cerro de Pasco
      Callao, Callao, Peru
  • 2002–2007
    • Universitas Hasanuddin
      • • Faculty of Medicine
      • • Jurusan Mikrobiologi
      Makassar, South Sulawesi, Indonesia
    • Centers for Disease Control and Prevention
      Atlanta, Michigan, United States
  • 2006
    • Ege University
      • Department of Microbiology and Clinical Microbiology
      İzmir, Izmir, Turkey
  • 2004
    • Yuzuncu Yil University
      • Faculty of Medicine
      Thospia, Van, Turkey
  • 2003
    • Instituto Evandro Chagas
      Ananindeua, Pará, Brazil
  • 2001–2003
    • Universidad de Navarra
      • Department of Urology
      Iruña, Navarre, Spain
  • 1988–1998
    • University of Amsterdam
      • Department of Medical Microbiology
      Amsterdamo, North Holland, Netherlands
  • 1993–1995
    • Leiden University Medical Centre
      • Department of Dermatology
      Leiden, South Holland, Netherlands
  • 1989–1995
    • Academisch Medisch Centrum Universiteit van Amsterdam
      • • Department of Virology
      • • Department of Medical Microbiology
      Amsterdamo, North Holland, Netherlands