Background

Money has served as an important means of exchange for goods and services for years. However, the public health implication of money as potential vehicle for parasites and microbes can have grave detrimental effect on human health as money is often transferred from one person to another (Oyero and Emikpe, 2007; Kuria et al., 2009; Mohamed et al., 2016). Money is generally used throughout the world as a medium of exchange for goods and services and a measure of value or means of payment. Furthermore, money is used as a measuring unit in pricing a transaction hence it is a store of value for our savings.

Human pathogens can be transferred directly through physical contact, or indirectly by many environmental materials such as air, water, food or other inanimate objects including money which can lead to widespread infection and diseases in human (Pope et al., 2002; Struthers and Westran, 2003; Emmanouil et al., 2014; Mohamed et al., 2016). While environmental factors of a particular geographical area play a pivotal role in the transmission of parasite and microbes to man, money serves as vehicles for these microbes (Pope et al., 2002; Kuria et al., 2009). Money, which is the most frequently used and circulated material in the world, are usually contaminated with various microbes and parasitic organisms as it is handled by people of varying health and hygienic standard and is stored under varying environmental and personal hygienic conditions (Kuria et al., 2009; Mbajiuka et al., 2014). These notes when poorly handled or saved, may lead to cross contamination by pathogenic zoonotic bacteria, fungus or any other parasitic infection. Bacteria are particularly found everywhere and their ability to contaminate objects such as naira notes is very prevalent when compared to parasites (Mbajiuka et al., 2014).

The abuse of the Nigerian naira became issues of public health in recent times and this motivated Central Bank of Nigeria (CBN) to embark on a nationwide campaign aimed at educating the public on the proper way of handling its national currency (Matur et al., 2010) Currently, there are eight denominations of the naira note form in Nigeria which include ₦5, ₦10, ₦20, ₦50, ₦100, ₦200, ₦500 and ₦1000 notes. The ₦5, ₦10, ₦20, ₦50, ₦100 and ₦200 naira notes are the most common and are more involved in daily cash transactions.

The aftermath effect of currency contamination can result to highly devastating public health condition for the entire populace. Reports from many part of the world such as Libya, Ghana, Egypt, Saudi Arabia and Sudan revealed that bank notes offers a large surface area for breading of pathogenic microbes and house many developmental stages of parasites, which could cause human diseases such as; meningitis, ulcer, tuberculosis, renal infections and gastro-intestinal infections (Podhajny, 2004). Contact with contaminated currency could also cause urinary tract infection, diarrhoea, septicemic infections etc. When hands used in cleaning up the anus after passing out faeces are not properly washed and are used to touch the Naira notes in any way, the tendency of contaminating it with trophozoite of the developed parasite, eggs, cyst or even the Oocyst is high. An individual living in unhygienic conditions having unhygienic habits will contaminate the notes with bacteria for example, improper hand washing after toilet, wetting of hand with saliva while counting money, coughing and sneezing on hands while exchanging money, and placement or storage of paper notes on dirty surface leads to the contamination and those notes will act as a vehicle delivering parasite and bacteria to contaminate the hand of the next users (Agersew, 2014).

Though, it is obvious from recent studies that money serves as agent or means by which diseases are transmitted from one individual to another in Nigeria and other Countries (Agersew, 2014; Leonard and Olajumoke, 2016), there are little or no information on the extent to which money serves as means of transmission in Akure metropolis. Furthermore, there is a need for constant monitoring of paper money for an updated data on parasites and bacteria as this will enhance policy making and, disease management and control. Therefore, this study aims to determine the extent of the parasitological and bacterial contamination of Nigeria currency notes and the antimicrobial resistance of the isolates in Akure, Nigeria.

1 Results

1.1 General characteristics of currency samples examined

A total of one hundred and sixty (160) Nigerian naira notes of varying denominations (including ₦5, ₦10, ₦20, ₦50, ₦100, ₦200, ₦500 and ₦1000) were collected and screened for possible contamination by parasite eggs/cysts and bacteria in both raining and dry season in Akure metropolis. Though, lower denominations such as ₦5, ₦10, ₦20, ₦50, ₦100 and ₦200 naira notes are the most common in circulation and are more involved in daily cash transactions, equal numbers of each denomination were sampled for reliable results. Microorganisms were not seen in all the 16 pieces of new and fresh Naira notes (mints) obtained from the financial institution on FUTA campus, which served as a negative control.

1.2 Relationship between denomination and contamination, season and contamination

Of the 160 samples investigated, 63 (39.4%) were found to be positive for parasite eggs/cysts. Generally, ₦100, 16 (80.0%) and ₦1000, 2 (10.0%) have the highest and lowest currency denomination contamination respectively. Additionally, the result significantly (x² = 39.95; p < 0.05) showed that ₦100 has the highest parasitic contamination of 70% and 90% in dry and wet season respectively while ₦1000 has the lowest parasitic contamination of 0% and 20% in dry and wet season respectively (Table 1).

Table 1 Frequency of Nigerian Naira Currency denomination contamination with parasite eggs/cysts according to seasons in Akure, southwest Nigeria

The frequency of occurrence of parasites eggs/cysts on Nigerian currency in Akure Metropolis varies significantly (Table 2). Of the 160 samples examined, a total of 224 parasites eggs/cysts were isolated. These include eggs/cysts of Enterobius vermicularis (8.9%), Hookworm (4.9%), Entamoeba histolytica (34.5%), Flagellates (5.4%), Ascaris sp. (29%), Strongyloides stercoralis (2.2%), Isospora sp. (3.1%) and Trichuris trichiura (12.9%). Entamoeba histolytica has the highest prevalence of 34.5% while Strongyloides stercoralis has the lowest prevalence of 2.2%.

Table 2 Frequency distribution of various parasite eggs/cysts on Nigerian Naira Currency Note in Akure, southwest Nigeria

Generally, an average total bacterial load of 2186.9 × 10³ cfu/mL was recorded for all the currency notes examined (Table 3). Of these, the highest bacterial load of 634.1 × 10³ cfu/mL was recorded on ₦200 notes while the lowest bacterial load of 54.3 × 10³ cfu/mL was recorded on ₦1000 notes. Furthermore, a higher average bacterial load of 1428.8 × 10³ cfu/mL was recorded on the 80 samples examined in wet season compared to a lower average total bacterial load of 758.1 × 10³cfu/mL observed on the 80 samples of the Naira notes examined in dry season (Table 3). In dry season, the highest bacteria load of 268.1 × 10³ cfu/mL was recorded on the ₦200 note while the lowest bacterial load of 10.8 × 10³ cfu/mL was recorded on ₦10 note. However in wet season, ₦100 has the highest bacterial load of 377.4 × 10³ cfu/mL while ₦1000 has the least bacterial load of 42 × 10³ cfu/mL. Statistical analysis reveal that there is significant different (x² = 62.63; df=7.5, p < 0.05) in the bacterial load observed in dry and wet season.

Table 3 Percentage Total bacteria Load on Nigerian Naira Currency Notes × 10³ (CFU/mL)

Eight bacterial species (Table 4) were isolated. The major bacterial species isolated from the samples examined are Staphylococcus aureus (23.1%), Escherichia coli (17.2%) and Pseudomonas sp (15.8%). During the dry season, S. aureus (23.0%) and Pseudomonas sp. (20.0%) have higher bacterial load than others while S. aureus (23.0%) and Escherichia coli (16.3) have higher bacterial load in wet season than others. There is significant different in the occurrence of the bacteria in the two seasons (x² = 40.05, p < 0.05).

Table 4 Frequency distribution of bacteria species load (CFU/mL) on Nigerian Naira Currency Notes with respect to season in Akure, southwest Nigeria

The antibiotic test for the Gram positive bacteria isolated are shown in Table 5. Staphylococcus aureus, Staphylococcus epidermides and Bacillus sp were tested with Gram positive antibiotic disc. Staphylococcus aureus showed resistance to six (6) out of the 8 antibiotics used, Staphylococcus epidermides showed resistance to two (2) while Bacillus sp showed resistance to four (4) of the antibiotics used. S. aureus is the most resistant while S. epidermides is the least resistant among all (Table 6).

Table 5 Antibiotics test for gram positive bacteria

Table 6 Antibiotics test for gram negative bacteria

2 Discussion

The isolation of parasitic and bacterial contaminants from the currency notes in this study has shown that currency served as an agent playing an important role in the transmission of pathogenic microorganisms. A prevalence rate of 39.4% was recorded for cysts/ova of parasites on dirty naira notes in Akure metropolis. This is in agreement with findings from other researchers such as Dada and Bellino (1979), Edungbola and Obi (1992), Orji et al. (2012) and Leonard and Olajumoke (2016) who showed that dirty naira notes are a potential source of contracting infections. In the same vein, studies have revealed that parasite cysts and ova are most prevalent on very dirty objects, mutilated materials and dirty currency notes while mint and clean notes harbors no parasite (Fashuyi, 1983; Awe et al., 2010). Obviously, the presence of these parasites on the Naira notes poses health risk to many people who may not wash their hands after counting dirty naira notes (Leonard and Olajumoke, 2016). A. lumbricoides and E. histolytica are transmitted orally by materials such as paper currency contaminated with the eggs and cysts of these parasites. Heavy infection with large number of Ascaris worms may cause abdominal pains or intestinal obstruction. E. histolytica causes the disease amoebiasis which is spread orally through ingestion of the cyst. The clinical symptoms of amoebiasis include amoebic dysentery, liver abscess or even death (Matur et al., 2010).

Though all the paper naira notes of the different currency denominations were generally observed to be contaminated with parasites, ₦100 notes have the highest prevalence of parasitic contamination and this is in line with the findings from other areas (Uneke and Ogbu, 2007; Leonard and Olajumoke, 2016). On the other hand, the polymer notes which include ₦5, ₦10, ₦20 and ₦50 notes examined had fewer parasitic contamination. The major reason for this disparity might be that the surfaces of naira notes made of paper can enhance the attachment of parasites and retain moisture for their survival. This result agrees with the record of Dehghani et al. (2011) who showed that the degree of contamination and types of microorganisms present on the currency notes is dependent on texture of the currency. The present report of the presence of parasites on the paper naira notes is in line with other studies (Matur et al., 2010; Elom et al., 2012; Leonard and Olajumoke, 2016).

Also, it is apparent from this study that bacteria are present on the paper naira notes. This suggests that the minimum conditions for their prevalence have been met (Awe et al., 2010). Dirty notes are usually moist and thus provide a good surface for bacterial growth. They provide favourable conditions such as substrate acquired from human body and dust from the environment. Most of the bacteria encountered in this current study are normal human body flora. This suggests that humans are the major source of bacteria on naira notes. The notes could have been colonized when placed in places where they make direct contact with the skin such as money kept in the brassiere. The skin harbors complex ecosystem of microorganisms, which could be transient or resident (Awe et al., 2010). The number of bacteria on the skin surface ranges from 103 cfu/cm² in dry areas to more than 107 cfu/cm² in moist areas (Willey et al., 2008). Similarly, colonization of the notes can occur due to practice like moistening the fingers with saliva when counting money (Awe et al., 2010). Money contact with the soil can also enhance its contamination. It is common practice to keep notes in contact with surfaces such as the ground, soil, table surfaces and so on. This is particularly common among traders and meat sellers. In the same vein, the presence of E. coli, Klebsiella sp. and Salmonella sp. suggest faecal contamination. These bacteria could have been introduced via contaminated water used to moisten the fingers while counting or cross contamination from offals. Improperly washed fingers after defecation especially among people with long finger nails could also be a source. Pseudomonas sp. is pathogenic when introduced into an immunocom promised individual who lacks normal defense mechanism in the body for example when mucus membrane or skins are disrupted by direct tissue damage. The organism attaches to and colonizes the mucus membrane or the skin, invades locally and produces systemic disease. The presence of these pathogenic bacteria reveals that the majority of people are exposed to contaminated currency notes. Unhygienic practices like indiscriminate coughing, sneezing, and defecation with indecent handling of currency notes could be the most common sources of contamination. Furthermore, the material from which the currency was manufactured is another factor that may affect the survival of microorganisms on the banknotes (Mohamed et al., 2016).

In Nigeria, cash transactions are used more frequently than credit cards, mobile transactions, and online transaction. The habit of keeping money in bags, pockets, brassieres, local pots and all other local means have been observed among the majority of Nigerians and this may contribute to high bacteria presence common on naira notes (Uneke and Ogbu, 2007; Leonard and Olajumoke, 2016).

Antibiotics susceptibility pattern revealed that organisms isolated have multiple antibiotic resistant patterns. The findings of Enerijiofi et al. (2016) and Oyero and Emikpe (2007) revealed that organisms isolated from naira notes were resistance to first line antibiotics and this was also observed in this study. The resistance observed might be due to the indiscriminate use of antibiotics by people especially those who get drugs from chemist store without any physician’s prescription (Enerijiofi et al., 2016). Bacterial agents like Staphylococcus, and E. coli have been known to develop resistance to commonly used antibiotics (WHO, 2000). The findings in this report support reports from other parts of the world such as United State of America (Pope et al., 2002), India (Nagesh et al., 2010), South Africa (Igunbor et al., 2007), Nepal (Janardan et al., 2009) and Ghana (Tagoe et al., 2010). The relative abundance of the normal skin flora and the transient bacteria that may be found on the skin could enhance an easy transfer to inanimate objects like currency notes (Adamu et al., 2012).

3 Materials and Methods

3.1 Study area

The study was carried out in Akure, the capital of Ondo State which lies between latitude 7^o13′ and 7^o19′ north of the equator and longitude 5^o07′ and 5^o14′ east of the Greenwich meridian. It has a population of 484,798 (NPC, 2006). There are two main seasons which include the dry season occurring between November to March and raining or wet season occurring between April to October with an average annual rainfall of 1500 mm. Akure has a temperature ranging from 21.4°C to 31.1°C and relative humidity of 80%. The economic activities of Akure city is great thus goods and services are exchanged for money among the community members. There are many tertiary and financial institutions which enhance continuous business transactions across the city.

3.2 Sample collection

A total of 160 samples of the Nigerian naira notes (10 pieces of each of the denominations of ₦5, ₦10, ₦20, ₦50, ₦100, ₦200, ₦500 and ₦1000 for each season; raining and dry totaling 20 pieces for each denomination) were randomly collected from different consented individuals and institution between January and July 2018. These include the bus conductors, taxi drivers, traders, market woman, students, hotels, food sellers, hospitals and other individuals in Oja-Oba market, Akure. Additionally, two pieces of new and fresh Naira notes (mint) of each denomination were obtained from the financial institution on FUTA campus, which served as a negative control. Coins were note sampled since they are no longer in circulation. Samples were collected in sterile polythene bags using disposable sterile hand gloves. The polythene bags were quickly sealed and the individuals were given another money equivalent to what was initially collected from them. The polythene bags were immediately transported to Research Laboratory, Department of Biology for parasitic and bacterial analysis.

3.3 Determination of microbial load

The bacterial load and identification was carried out using the modified method described by Girma et al. (2014). In this method, sterile cotton swab moistened with buffered peptone water solution was used to swab well on both side of each naira paper note placed on pre-sterilized aluminum foil that was larger than the size of the naira paper notes. The swabs were then separately soaked into 15 mL buffered peptone water solution and kept in refrigerator at 4^oC till microbial analysis was carried out on the samples in less than two hours maximum. Later, 1 mL of each naira paper note swab sample was transferred aseptically into 9 mL of buffered peptone water (BPW) and thoroughly mixed using votex and a serial dilution was made from 1:10^-1, 1:10^-2, 1:10^-3… 1:10^-6. This was done by transferring 1 mL of test sample into 9 mL of sterile water in a test tube on test tube rack, using sterile needle and syringe to make delusion 1:10^-1. The tube was caped back and mixed vertically and then 1 mL was transferred from it into the next tube using a new sterile syringe and needle. This was repeated on till 10^-5. A 1.0 mL of the test dilution (after agitation) from 1:10^-3 was dispensed onto plate and media was poured on it and spread evenly in the plate. Five different media; Monitor Salt Agar (MSA), Centrimide agar, Deoxychocolate agar (DCA), MacConkey Agar and Nutrient agar (NA) were used. All plates were incubated at 37°C, aerobically in an incubator overnight. After overnight incubation, all colonies on the plates containing 30~300 colonies were counted from the duplicate plates and the mean counts determined.

3.4 Parasitological analysis

Standard concentration techniques for the isolation of enteric parasites were used as described by Cheesbrough (1998) and World Health Organization (2003). The remaining solution was transferred into a centrifuge tube and centrifuged at 2,000 g for 5 minutes. The supernatant was decanted while the sediment was stirred and a drop of the sediment was placed on sterile clean glass slide, stained with Lugol’s iodine and covered with cover slip and examined microscopically at varying magnification from ×4, ×10, ×40 and ×100 for the presence of parasite eggs and cysts. Identification of parasites was made according to standard guidelines (WHO, 2004).

3.5 Isolation and identification of Bacteria

Plates with mixed cultured were further subculture in order to get pure culture or colonies. Identification of the isolates was done by observing the colonial morphology, cellular morphology using Gram staining procedure and Biochemical tests using conventional method.

3.6 Gram staining

A smear of colonies isolated was made on a glass slide using wire loop. It was dried and heat fixed. Then, the fixed smear was flooded with crystal violet solution for 60 s and washed. This was later tipped off and covered with lugo’s lodine for 60 s. This was then washed off and decolorized with 70% ethanol. The smear was then flooded with safranin solution for 60 s and then rinsed with water and air dried.

3.7 Microscopy

The back of the glass slide was wiped clean and a drop of colourless thick oil (glycerin) was applied on the smear which was examined microscopically with x100 objectives for the observation of grams reactions and morphological characteristics of the bacteria cell. Positive bacteria did not decolourized with ethanol and hence their cells appear dark purple in colour, while gram negative cells retained the counter staining colour of safranin and hence appear pink in colour.

3.8 Statistical analysis

Data were analyzed using Statistical Package for Social Sciences (SPSS) software version 20.0. Appropriate descriptive statistics such as frequency was used. The p-value was calculated using chi square test. The significant difference was considered at 95% confidence interval (p<0.05).

Authors’ contributions

OTA conceived and designed the study, AOB and AT collected the data and analyzed it, OTA, AOB and AT wrote the manuscript and approved it. All authors read and approved the final manuscript.

Acknowledgements

We sincerely appreciate the contribution of those who participate in money exchange for this research.

References

Adamu J.Y., Jairus Y., and Ameh J.A., 2012, Bacterial contaminant of Nigerian currency notes and associated risk factors, Research journal of Medical sciences, 6(1): 1-6

https://doi.org/10.3923/rjmsci.2012.1.6

Agersew A., 2014, Microbial contamination of currency notes and coin in circulation: A potential of public health hazard, Biomedicine and biotechnology, 2(3): 46-53

Awe S., Eniola K.I., Ojo F.T., and Sani A., 2010, Bacteriological quality of some Nigerian currencies in circulation, African Journal of Microbiology Research, 4(21): 2231-2234

Cheesbrough M., 1998, District Laboratory Practice in Tropical Countries, Part 1. Cambridge, UK: Cambridge University Press

Dada B.J.O., and Bellino E.D., 1979, Prevalence and public health significance of Helminthes Ova in Dog faeces deposited on the street of Zaira, Nigeria, Annals of Tropical Medicine and parasitology, 73(5): 89-90

https://doi.org/10.1080/00034983.1979.11687290
PMid:534450

Dehghani M., Dehghani V., and Estakhr J., 2011, Survey of Microbial Contamination of Iranian Currency Papers, Research Journal of Pharmaceutical, Biological and Chemical Sciences, 2(3): 242-248

Edungbola L.D. and Obi A.A., 1992, A review of human intestinal parasites in Nigeria; challenges and prospects for integrated control, Nigerian Journal of Parasitology, 13: 27-37

Elom M.O., Alo M.N., Ezike A.C., Okeh E.N., and Anyim C., 2012, Parasitic helminthes on Nigerian currency: A public health jeopardy, Prime Journal of Microbiology Research PJMR, 26: 165-169

Emmanouil A., Esam I.A., Fehmida B., Muhammad Y., Ahmed K.A., Ahmad M.A., Adel G.E., and Didier R. 2014, Paper money and coins as potential vectors of transmissible disease, Future Microbiol, 9(2): 249-261

https://doi.org/10.2217/fmb.13.161
PMid:24571076

Enerijiofi K.E. and Olatunji E.O., 2016, Microbial Contamination and Antibiotics Resistance Pattern of Isolates from Naira Notes in Some Markets in Esan Land, Edo State, Nigerian Journal of Microbiology, 30(1): 3345-3349

Fashuyi S.A., 1983, The Prevalence of Helminthes eggs in human faeces deposited on the Streets of Lagos, West African Medical Journal, 2: 135-138

Girma G., Ketem T., and Bacha K., 2014, Microbial load and safety of paper currencies from some food vendors in Jimma Town, Southwest Ethiopia, BMC Research Notes, 7: 843

https://doi.org/10.1186/1756-0500-7-843
PMid:25424723 PMCid:PMC4255439

Igunbor E.O., Obi C.L., Beasong P.O., Potgiester N. and Mkasi T.C., 2007, Microbiological analysis of Banknotes circulating in the venda region of Limpopo province, South African, Journal of science, 103: 365-366.

Janardan L., Satish A., Prson G., Ranjani M., and Bishal D., 2009, Risk of handling paper currency in circulation: chances of potential bacterial transmittance, Nepal Journal of Science of Technology, 10: 805-807

Kuria J.K., Wahome R.G., Jobalamin M., and Kariuki S.M., 2009, Profile of bacteria and fungi on money coins, East African Medical Journal, 86(4): 151‐155

https://doi.org/10.4314/eamj.v86i4.46943

Leonard O., and Olajumoke M., 2016, Parasite Contamination of Nigerian Currencies in Ibadan City, South-West Nigeria, Annual Research & Review in Biology, 10(6): 1-6

https://doi.org/10.9734/ARRB/2016/24735

Matur M.B., Malann D.Y., and Yvoun E., 2010, Survey of parasite cysts, eggs and bacteria on Nigerian currency in FCT, Abuja, New York Science Journal, 3(1): 10-13

Mbajiuka C.S., Obeagu E.I., Nwosu D.C., and Agbo C.E., 2014, Microbiological Evaluation of Naira Notes Handled by Fish Sellers in Umuahia Metropolis, World Engineering & Applied Sciences Journal, 5(2): 44-52

Mohamed M.E., Abdulgader D., Mahmoud B.S., and Khaled D., 2016, A study of Bacteria Contamination on Libyan Paper Banknotes in Circulation, American Journal of Microbiology and Biotechnology, 3(1): 1-6

Nagesh B., Bhat S., Asawa K., and Agarwal A., 2010, An assessment of the oral health risk associated with handling of currency notes, International Journal of Dental Clinic, 2: 14-16

National Population Commission, 2009, National Population Census Federal Republic of Nigeria Official Gazette, 96(2)

Orji N., Esiaka E., Anyaegbunam L., Obi R., and Ezeagwuna D., 2012, Parasite Contamination of Nigerian Currency (Paper and Polymer Notes) in the Ihiala Local Government Area of Anambera State, Nigeria. The Internet Journal of Infectious Diseases, 10(1)

https://doi.org/10.5580/2a7c

Oyero O.G., and Emikpe B.O., 2007, Preliminary investigation on the microbial contamination of Nigerian currency, Int J Trop Med, 2(2): 29-32

Podhajny R.M., 2004, How dirty is your money?. Paper, film and foil converter, 78(1): 21

Pope T.W., Ender P.T., Woelk W.K., Koroscil M.A., and Koroscil T.M., 2002, Bacterial Contamination of Paper Currency, Southern Medical Journal, 95: 1408- 1410

https://doi.org/10.1097/00007611-200295120-00011
PMid:1259730

Tagoe D.N.A., Baidoo S.E., Dadzie I., and Ahator D., 2010, A study of Bacterial Contamination of Ghanaian Currency Notes in Circulation, The Internet Journal of Microbiology, 8 (2): 1-5

https://doi.org/10.5580/c78

Uneke C.J., and Ogbu O., 2007, Potential for parasite and bacterial transmission by paper currency in Nigeria, J Environ Health, 69: 54

Struthers J.K. and Westran R.P., 2003, Clinical Bacteriology ASM Press, Washington, D.C,. https://trove.nla.gov.au/version/37354639

https://doi.org/10.1128/9781555812768

Willey J.M., Sherwood L.M., and Woolverton C.J., 2008, Prescott, Harley, and Klein’s Microbiology 7^th Edition, McGraw-Hill, London, 113-118

World Health Organization (WHO), 2000, Overcoming antimicrobial resistance. Retrieved May 5, 2005, from http://www.who.int/infectious-disease-report/2000/

World Health Organization (WHO), 2003, Manual of basic techniques for a health Laboratory (2nd ed.). Geneva: Author

World Health Organization (WHO), 2004, Bench aids for the diagnosis of intestinal parasites. Geneva: Author