5.1 Pre-travel preparations
“Occupational travel to tropical countries among Germans has more than doubled in the past five years” (Jansing et al. 2021). The number of young volunteers going abroad has also increased tremendously in the last decade (Anonymous 2019), including the number of international travels in general. Health related issues occur for a good number of travelers. Therefore, this needs to be addressed, particularly regarding the higher exposure to tropical infections among volunteers and aid workers often living in rural regions for longer periods (months or even years). As other studies have already shown, risk behavior and risk perception among volunteers depends strongly on the intensity of pre travel training and medical advice given (Jansing et al. 2021), (Han, Balaban, and Marano 2010). The importance of information on preventive behavior and education in self-management skills before travel was stated by a recent study (Sasayama, Gilmour, and Ota 2021). This particular study showed that even after having taken a health lecture, only 40% of people knew about the more dangerous risks like malaria and dengue. Obviously, just hearing about a health lecture is not sufficient for volunteers to understand the severity of existing health hazards they will be exposed to in the regions they visit. Specific training to develop self-management skills is therefore crucial for their better understanding of potential threats and how to react upon them. Studies have also addressed the issue of proper preparation (Sasayama, Gilmour, and Ota 2021). In another survey, only 70% of relief aid workers interviewed stated to have taken a pre-travel medical examination and only every fourth person had used a mosquito-net or repellents to protect themselves against malaria or dengue fever (Sharp et al. 2006). Regarding international travel, “malaria especially, continues to threaten international travelers due to inadequate perception of risk and sub-optimal pre-travel preparations” (Angelo et al. 2017).
These previously described risky behaviors, seem indeed to represent one of the biggest risks, causing diseases such as malaria and dengue to occur more frequently than necessary. Not only do volunteers behave risky despite pre-travel health advice (Martin et al. 2012), (Küpper et al. 2014), but studies have shown, especially regarding malaria prevention, that young people are clearly not well informed about this specific risk. Landman et al (3013) reported that adherence to malaria prophylaxis was moderate due to the fear of long-term adverse events. One out of four even reported “not worrying about malaria” although living and working in high risk regions (Landman, Tan, and Arguin 2013). This shows that there is a need of increasing information and training about prophylactic efficacy and likelihood of side effects.
Volunteers do not only have a higher risk profile than older aid workers, but they also travel to regions with underestimated health hazards resulting in possible health issues during and after their stay abroad. Therefore, not only pre-travel preparation is an ongoing issue but also the importance of medical follow ups. According to a study done in the United Kingdom in 2006 – 2007, 27% of volunteers returned from voluntary services overseas with ongoing unresolved medical problems (Bhatta et al. 2009) and more than one third of aid workers interviewed “reported worse health on return than before their mission” (Dahlgren et al. 2009). Another study found that 53% of the travelers presented themselves to hospital within one week of return and 96% within 6 months after coming back from overseas due to health problems” (O'Brien et al. 2001).
5.2 Sub-Saharan risk-regions and malaria risk
For the occurrence of occupational diseases analysed in our study, a disproportionate risk of being diagnosed with a tropical disease, above all other diseases, malaria was detected in volunteers living in Africa and especially those in Sub-Saharan / West African regions (Figure 3). Most of them were diagnosed with malaria and many of those with malaria tropica (Pl. falciparum). It is evident that the risk for malaria is higher there, as the region of West Africa, is in fact stated by the World Health Organization (WHO) as a region with an all-year high malaria risk (Anonymous 2020a). In 2020, 95% of all malaria cases were observed in Sub-Saharan-regions (Anonymus 2021). International data has already shown, that “travel to Sub-Saharan Africa and Oceania was associated with the greatest relative risk of acquiring malaria” (Angelo et al. 2017). Nonetheless results from a survey for Spanish travelers showed again the lack of potential pre-travel preventive measures as more than one third of travelers to Sub-Saharan Africa received no malaria prophylaxis (Lopez‐Velez and Bayas 2007). Even more important is the preparation and importance of raising region-specific awareness for the existing health hazards for volunteers or travelers beforehand as these are the best measures to prevent an infection through a mosquito-bite.
In current study, malaria was found to be diagnosed more often among volunteers than among humanitarian aid workers and other short or long-term aid workers for the time period investigated, even though the cases of aid workers analysed in this study showed a long travel history, traveling abroad over and over to risk countries due to their work contracts. According to the volunteer cases, their stay for the voluntary service abroad was often their first travel to a tropical region involving new health hazards. The time taken from departure up to diagnosis was significantly shorter for volunteers compared to the aid workers (p<0.01), having most of the first diagnosis halfway through their voluntary year. Aid workers were diagnosed after a much longer stay abroad and data in this study showed that aid workers did not have more episodes of malaria whilst staying on average three times longer abroad, unlike volunteers who had up to five episodes of malaria during their shorter stay. These findings suggest continuously missing or not sufficient compliance for preventive measures, especially regarding the prevention of getting malaria through mosquito bites.
According to our findings, the risk of infection with malaria pathogen did not increase proportionally with the length of stay but there was a correlation between the stay in African regions and an infection with malaria pathogen, especially plasmodium falciparum causing malaria tropica and harboring the risk of a severe or even life-threatening case of malaria (Figure 4). A significant increased risk for the infection with plasmodium falciparum in West Africa could not be proven. There could be up to one fourth more infections with Plasmodium falciparum since 23.6% of the malaria diagnoses were made upon a positive test result of a rapid diagnostic test (RDT). Unfortunately, the types of malaria pathogen tested positive could not be detected from the data of the RDT tests.
Other studies have likewise found out, that especially travelers being exposed in Sub-Saharan regions were mostly diagnosed with malaria tropica (Angelo et al. 2017) and this supports our current hypothesis that there is a greater and often underestimated risk among young volunteers going abroad for the first time.
5.3 Suspicions for occupational diseases
More cases of suspected occupational diseases were reported among volunteers than among others, mostly aid workers, represented in this study. Malaria was shown to occur more frequently among the volunteers whereas the diagnosis for dengue fever occurred equally within both groups. The infection with dengue transmitted by a mosquito bite is only preventable with adequate use of repellents and mosquito-nets at night (Gupta and Rutledge 1994) whereas an infection with malaria pathogen can additionally be prevented through adequate chemoprophylaxis (Nauck 1956). Sadly, studies have shown how very little travelers know about the efficacy of the use of anti-malaria chemoprophylaxis or – even more effective – mosquito nets to sleep under them, and therefore the lack of taking or using them for prevention (Lopez‐Velez and Bayas 2007), (Landman, Tan, and Arguin 2013). These findings suggest that volunteers do take higher risks in terms of prevention, causing more and repeated infections with malaria parasites and leading to preventable occupational diseases.
Similar behavior must be assumed regarding the lack in prevention measures taken to protect oneself against mosquito bites transferring dengue or also chikungunya. The lack of knowledge (Sasayama, Gilmour, and Ota 2021), risk perception or even willingness to protect oneself against dengue with bed nets and the daily use of repellents or chemoprophylaxis especially among young volunteers leads again to potentially preventable case numbers of tropical occupational diseases (BK-3104). Considering the geographic localization of dengue cases investigated in this study, there were significantly more dengue cases and especially among volunteers who traveled to India for their service (Figure 5). In current study, the different regions of India with dengue cases could not be differentiated as data were not detailed enough in the health reports analysed. Since India is a very popular country volunteers go to (Figure 1), it is crucial to enlighten them on potentially underestimated risk of acquiring dengue fever whilst traveling there. The WHO classified dengue risk regions in Asia as representing 70% of the global burden of the disease (Anonymous 2021c). A study analysing dengue in peace corps volunteers found the Caribbean to have highest number of dengue cases followed by East Asia and South/East Asia regions (Ferguson et al. 2016). In contrast, Latin America, where the most important number of volunteers are sent every year, did not report many cases of dengue fever. According to the WHO, a significant reduction of dengue cases was reported in the Americas in 2017 although dengue cases are increasing worldwide in the supervised risk regions with highest number of cases reported in Bangladesh, Malaysia, Philippines and Vietnam in Asia (Anonymous 2021c). Attention must therefore also be paid to increasing risk for infection with dengue worldwide especially in tropical and subtropical regions as the number of dengue cases reported to the WHO increased over 8 fold in the last two decades putting half of the world’s population at risk (Anonymous 2021c).
For the occurrence of typhoid (enteric) fever, no case could be recommended for the recognition as an occupational disease as a diagnosis based on positivity of the old and unreliable Widal test alone could not be accepted, especially if clinical signs were either not reported or not compatible with a diagnosis of typhoid fever. Nonetheless attention should be paid to this infectious disease found in the tropics, highly correlating with a high fecal contamination of sanitary facilities in big cities, not only affecting locals but also travelers and workers (Abhilasha et al. 2008). As gastrointestinal symptoms are often self-limiting and diagnostic methods are insufficient, recognition of typhoid fever is often difficult because stool tests are often negative in the first week and serological tests may be positive at a late stage of disease only or never. The traditional Widal-Test shows a low sensitivity of 65.4%, specificity of 89.8%, and accuracy of 82.1% (Maheshwari et al. 2016), (Shahapur et al. 2021). Therefore, prevention measures regarding water transmitted diseases like typhoid fever must also be addressed during training seminars as volunteers do not always have access to safe drinking water and sanitary facilities (Martin et al. 2012). It may be expected that typhoid fever is more common when more people were sent to south-east Asia, especially to Nepal and India as these countries have the highest rate of typhoid fever worldwide (Karkey et al. 2016), (Abhilasha et al. 2008).
Infestations with schistosomiasis were significantly more frequently diagnosed among aid workers, mostly based on a positive serology after their return from overseas. This may be a consequence of the longer stay of aid workers. However, there are other factors which should be taken into consideration, e.g. individual behavior: Volunteers may have had some swimming or water diving activities which often takes place far from the shore while aid workers may have walked in the water at the shore to cool down. By this, their risk would be significantly higher than those of volunteers. Housing may also be an important factor: Do people get their water as rainwater or from a pond? Unfortunately, such factors are usually not documented or reported and therefore the underlying risk factors must remain as such. Only few cases of schistosomiasis were recommended to be accepted as occupational disease, due to the fact that in most cases, single serological tests do not constitute a diagnosis in the absence of parasitological proof and that the attribution of such a positive serology to a certain exposure is often impossible (Anonymous 2017). A single serological test may be accepted as proven diagnosis, only if the person went to a risk area for the first time and the titers are high. However, an element of risk remains because in non-endemic countries some species of schistosomiasis occur, e.g. Cavu River in Corsica, and trichobilharzia occurs in Europe’s swimming lakes if there are many ducks (Effelsberg 1989). These factors may cause false-positive results. Some tests may also be negatively affected antibody cross reactions (Homsana et al. 2020). With such risk elements in mind a single serological test may be acceptable in some cases but a significant shift of titers is still “Gold Standard”. Diagnostic methods like the Rapid dipstick point of care test (POC) are insufficient (Ochodo et al. 2015).
Interestingly, volunteers were mostly diagnosed in their host country with the above-mentioned rapid dipstick test. Not accepting a positive POC test as valid diagnosis doesn’t exclude the possibility of a schistosomiasis as the test proves the contact to the pathogen but not an active infestation (Kapaun 2004) (Casacuberta-Partal et al. 2020a). Two positive serology samples or microscopic detection of the pathogen are necessary to prove an active infection with schistosomiasis pathogen (Anonymous last updated version 10/2017)
These secure detection methods where fairly used among volunteers. A schistosomiasis screening for antibodies and preferably followed by the more sensitive up-converting phosphor lateral flow circulating anodic antigen (UPC-LF CAA) test should be encouraged after freshwater contact (Anonymous last updated version 10/2017)
(Casacuberta-Partal et al. 2020a). In high-endemic areas serology should be analysed 12 weeks after return (Anonymous 2017), (Kapaun 2004) to detect potentially active infestations with low burden of schistosomiasis pathogen after staying abroad, as travelers may be asymptomatic on first presentation (Casacuberta-Partal et al. 2020b) and infections need to be treated early in order to prevent long-term complications in the case of chronic schistosomiasis, as liver fibrosis (Zhong et al. 2022), bladder cancer (Efared et al. 2022)and other chronic inflammations (Musaigwa et al. 2022).
5.Personal protection measures
The effectiveness of repellents and the use of insecticide impregnated bed-nets should be encouraged in order to achieve better prevention. Pre-travel checkup and mandatory follow up examinations are crucial to be able to attribute a suspected diagnosis of an illness to the past journey and to accept it as an occupational disease which occurred during the actual journey.
Unfortunately, in this study it was impossible to assess whether volunteers took recommended prevention measures like malaria chemoprophylaxis or other, non-drug-related precautions like the use of repellents or mosquito-nets according to the risk associated to particular regions they were travelling to. However, Martin et al. reported that there are deficiencies in such strategies in young people, even more pronounced than in elderly persons (Martin et al. 2012). It was impossible to track what kind of specific training and quality of medical checkups were done before the departure. Further, investigations are necessary to assess the type and adequacy in terms of preventive measures taken before, during and after travel.
Another limitation of this study is the limitation on specific pathogens considered in this study. According to the regulations, other diseases than the ones listed as occupational diseases may be accepted as occupational disease by the insurance if the occupation is at least likely the situation where the patient got the infection. The German regulations include two options here: Bk-3102 (“diseases which may be transmitted from animals to humans”) or by the so-called “extension condition”. This includes cases which are not listed as occupational disease but where the occupational exposure can be proven as the main or only risk. The former could be the case if an African tick bite fever was diagnosed. Rickettsioses were recently identified as rapidly emerging diseases and probably they are more common in returning travelers than malaria (Jensenius et al. 2003), (Jensenius et al. 2002), (Cherry et al. 2018), (Leder et al. 2013), (Bottieau et al. 2006). However, such diagnoses never occur so far in the applications for occupational disease. The latter option may be chosen when a person who is active in nature protection in national parks get anthrax. Such cases rarely occur in Namibia and Zambia, probably also in other countries, e.g. Botswana (Rob Clifford, South Luangwa Valley, personal communication 2020). Because of the total number of cases especially concerning rickettsioses more awareness of the counselling physicians is desirable.