Work

Comments on “Screening US Vietnam Veterans for Liver Fluke Exposure 5 Decades After the End of the War”

Year: 2018

Type: article

Abstract: To the Editor: We have read with great interest the article by Psevdos et al1 on screening US Veterans of the Vietnam War for exposure to liver flukes, an endemic public health issue in Southeast Asia. We commend the authors for undertaking this investigation of an important knowledge gap concerning the risk of these types of infections in both veterans and, potentially, in active duty military serving in endemic areas. However, the authors concluded that their study “provides evidence of exposure to the liver fluke parasites in US soldiers during their service in the Vietnam War.” This conclusion may potentially overstate the strength of their findings. Foremost, the method description in the present article contains no details beyond that a multihelminth antigen assay (not Food and Drug Administration approved), which includes a crude whole worm Clonorchis antigen preparation, was used to detect antibodies to Opisthorchis (the likely parasite that these veterans were exposed to in Vietnam). In the cited multihelminthic study,2 there were no stated positive or negative controls and present, past, and cross reactive antibodies could not be determined. In this and another study,3 the authors rely on the potential cross reactivity with Clonorchis to detect the presence of Opisthorchis antibodies, but the extent to which this actually occurs with this particular test is not described. Also, as noted by Psevdos et al,1 there may be significant cross reactivity between other helminths with this assay. We believe that use of appropriate positive and negative controls would have better clarified the meaning of detected antibodies. Without these controls, it is difficult to conclude whether the positive results are more likely to represent true prior infections or false positives. Although it is very possible that some veterans were exposed to hepatobiliary flukes in the Vietnam War Theater, determining whether such exposures resulted in long-term health consequences or are adversely affecting the health of Vietnam veterans today will be challenging. Hepatobiliary flukes have been documented to live for 20 to 30 years.4 Because it has been 5 decades since the Vietnam War, veterans are unlikely to still harbor active infections, and indeed none were found in the study by Psevdos et al.1 Furthermore, the risk of complications, such as cholangiocarcinoma, is likely related to the intensity of the fluke infection, which in infected veterans may have been low compared with endemic populations who may regularly consume undercooked or raw fish.5 Even in infected immigrant populations diagnosed in the United States, cholangiocarcinoma is rare.6 The authors state, “Based on our pilot findings, we recommend an epidemiological study using a larger patient sample for serological testing using a specific Opisthorchis viverrini antigen.” We fully agree with the need for more studies to determine whether these flukes pose a threat to current or past military personnel. There are several types of epidemiological studies that could be done in the near future in Vietnam veterans, such as studying incidence of or mortality from cholangiocarcinoma (recognizing there are other risk factors), or conducting a case control study, because this is a very rare cancer with an incidence rate of about 2/100,000.7 Possible future development of more sensitive and specific assays for these infections, including nucleic acid–based tests on stool samples and/or serological studies specific for each species of fluke (potentially with recombinant antigens) might also enhance our ability to measure the past and current risk of these parasites to veterans and active military personnel. However, these are not currently in existence and would have to be developed and rigorously tested for clinical validity before any potential usage in any large scale research. Finally, the findings from this pilot study by Psevdos et al,1 although important in acknowledging a health concern of Vietnam veterans, are not sufficient to change clinical practice at this time. Instead, we encourage clinicians to educate concerned patients as to their low risk of cholangiocarcinoma and also discuss other more common causes of liver cancer including the viruses hepatitis B and C. We encourage interested clinicians and veterans to access the following Department of Veterans Affairs website at https://www.publichealth.va.gov/exposures/infectious-diseases/cholangiocarcinoma.asp, which is linked to a number of recently updated Centers for Disease Control and Prevention websites on these topics, which are reachable through https://www.cdc.gov/parasites/liver_flukes/. As far as clinical management, the Centers for Disease Control and Prevention states, “Serologic testing for Opisthorchis is not useful for patient management and is not available in the United States”.8 At present, we agree with that assessment, and thank you for letting us comment on this research article and the importance of this topic in general. Theodore E. Nash, MD Laboratory of Parasitic Diseases National Institute of Allergy and Infectious Diseases National Institutes of Health Bethesda, MDDavid Sullivan, MD Department of Molecular Microbiology and Immunology Johns Hopkins Bloomberg School of Public Health Baltimore, MDEdward Mitre, MD Department of Microbiology and Immunology Uniformed Services University of the Health Sciences Bethesda, MDEric Garges, MD, MPH, MTM&H (LTC, MC) Division of Tropical Public Health Department of Preventive Medicine Uniformed Services University of the Health Sciences Bethesda, MDVictoria J. Davey, PhD, MPH Office of Research and Development Department of Veteran Affairs Washington, DCGary Roselle, MD National Infectious Diseases Service Department of Veteran Affairs Cincinnati, OHStephen J. Davies, BVSc, PhD Department of Microbiology and Immunology Uniformed Services University of the Health Sciences Bethesda, MDPeter D. Rumm, MD, MPH Post Deployment Health Services Department of Veteran Affairs Washington, DC [email protected]

Source: Infectious Diseases in Clinical Practice

DOI: 10.1097/ipc.0000000000000659