The authors are grateful to the Direcci&#243;n General de Asuntos del Personal Acad&#233;mico of the Universidad Nacional Aut&#243;noma de M&#233;xico for providing the financial resources through grant PAPIIT IN218720 and to Dr. Claudia Mendoza for granting the requested extension. This work is dedicated to my lovely Nicole, who passed away in 2019. You will always live in my heart.

The use and care of dogs was approved by the National and Autonomous University of Mexico.
1. Collection of fecal samples
NOTE: Handle the dog with the help of a veterinarian or the owner of the animal.
<ol>
	<li>In the case of feral dogs (Figure 1A) or nervous animals, collect samples from the ground right after defecation or no more than 10 min later.</li>
	<li>Lubricate surgical gloves or thin-walled polyethylene bags with water or Vaseline. To collect fecal samples from the rectum, wear surgical gloves or thin-walled polyethylene bags.</li>
	<li>Collect at least 2 g of feces from each dog (Figure 1B).</li>
	<li>Identify individual fecal samples as follows: date, location (Global Positioning System [GPS] coordinates using Google Maps), assign an identification number for each animal, approximate age of the dog, gender of the dog, breed, indoor or outdoor (feral) dog.</li>
	<li>Close the bags containing the fecal sample with a tight knot. Keep the bags refrigerated (4-8 &#176;C) if stool samples are not analyzed within 3-4 h after collection.</li>
</ol>
2. Preparation of a saturated salt solution for field diagnosis
NOTE: If access to a balance, measuring material, stoves, or gas to boil water is absent or limited, the saturated saline solution can be easily prepared using water, common table salt, a plastic 12 oz (355 mL) cup, and a 1 L soda plastic empty bottle.
<ol>
	<li>Wash thoroughly an empty 1 L soda bottle. Fill the bottle with 1 L of water.</li>
	<li>Fill a 12 oz plastic cup with common table salt.</li>
	<li>Transfer the salt to the soda bottle.</li>
	<li>Close tightly the soda bottle with the screw cap. Shake the solution vigorously until the salt no longer dissolves. 
	NOTE: Shaking the solution in the soda bottle until complete dissolution of salt can take up to 90 min.</li>
</ol>
3. Preparation of a saturated salt solution for laboratory diagnosis
<ol>
	<li>Weigh 420 g of common table salt.</li>
	<li>Dissolve 420 g of salt in 1 L of water.</li>
	<li>Boil the solution until no more salt dissolves.</li>
	<li>Filter the solution to discard the undissolved salt.</li>
	<li>Check the concentration of the solution using a heavy fluid hydrometer or densitometer. 
	NOTE: The ideal concentration has an SpG of 1.20 to achieve better results (Figure 2A). The floating capability of an egg is influenced by its interaction with the solution, contributing to the varying ability of eggs to float in solutions with the same specific gravity. Hence, to achieve optimal egg recovery, it is essential to consider the upper range of specific gravity in the flotation solution, ensuring it surpasses that of the targeted parasite elements6.</li>
</ol>
4. Flotation method
NOTE: If fecal samples are too dry or hard, macerate them in a mortar.
<ol>
	<li>Using a spoon, place approximately 3 g of feces in one plastic cup (~8.5 cm in height and ~5.5 cm in diameter).</li>
	<li>Add 1 mL of the saturated salt solution until a paste is obtained.</li>
	<li>Stir for 1 min and add 100 mL of saturated salt solution.</li>
	<li>Pass this suspension through a plastic strainer into a second plastic cup to avoid coarse particles (Figure 2B).</li>
	<li>Let the suspension stand for 15-20 min.</li>
	<li>Place an inoculation loop in a flame for 1 s to ensure it is free of eggs, cysts, or oocysts (Figure 2C).</li>
	<li>Wait for 5 s for the inoculation loop to cool down (Figure 2D).</li>
	<li>Take three drops from the surface of the suspension with the inoculation loop. Place each one of the three drops separately on one glass slide (Figure 2E-G) 
	NOTE: Ensure that the drops are not in contact with each other (Figure 2H).</li>
	<li>Observe under the microscope with a 10x objective (Figure 2I). Place a coverslip if magnification is increased to 40x.</li>
	<li>When a positive result is observed in the droplet, assign a cross (+) in the laboratory logbook to record the presence of parasites in the patent period in random sites of the fecal suspension surface.</li>
</ol>
5. Interpretation of the flotation method
NOTE: Negative results are inconclusive.
<ol>
	<li>Perform a series of three tests with samples from 3 consecutive days to increase the sensitivity of the test. 
	NOTE: Positive results indicate the presence of parasites in the patent period.</li>
</ol>

Recognition of Zoonotic Roundworms by a Fecal Flotation Technique

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The authors have no conflicts of interest to disclose.

Nematodes such as T. canis and Ancylostoma spp. can inhabit the small intestine of dogs and have the potential to be transmitted to humans. Clinical signs caused by T. canis are serious in young dogs, manifesting as poor growth, respiratory issues, or digestive tract lesions28. In adult dogs, the infection typically tends to be mild. Diagnosis relies on identifying characteristic eggs in a fecal sample. This condition is a frequent cause for prescribing anthelmintic trea...

Gastrointestinal parasites are one of the most common health problems that affect dogs1. Estimates suggest that there are ~700 million domestic dogs worldwide, and approximately 175 million may be categorized as free-roaming2. More than 60 parasite species are shared between dogs and humans, suggesting that dogs could be a source of infection for humans with these parasites3. Toxocara canis and Ancylostoma caninum are two parasitic species that infect dogs and, accidentally, human hosts. Currently, there are several studies about the locations where these helminths are able to survive and reproduce in Mexico. The prevalence of Toxocara in dogs varies from 0% to over 87% across the United States, Mexico, Central America, and the Caribbean4. Toxocara canis and Ancylostoma spp., as well as other parasitic species in dogs, have been previously reported in Mexico5,6,7,8,9,10,11,12,13&#160;(Table 1).
<table border="1" fo:font-size="8px" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Parasitic species</td>
			<td>Region</td>
			<td>Prevalence (%)</td>
			<td>Reference</td>
		</tr>
		<tr>
			<td rowspan="4">Ancylostoma caninum</td>
			<td>Quer&#233;taro</td>
			<td>42.90</td>
			<td>5</td>
		</tr>
		<tr>
			<td>Tabasco</td>
			<td>15.90</td>
			<td>6</td>
		</tr>
		<tr>
			<td>Campeche</td>
			<td>35.7 &#8211; 42.9&#160;</td>
			<td>7</td>
		</tr>
		<tr>
			<td>Yucat&#225;n</td>
			<td>73.8</td>
			<td>8</td>
		</tr>
		<tr>
			<td rowspan="2">Babesia</td>
			<td>Morelos</td>
			<td>13.60</td>
			<td rowspan="2">9</td>
		</tr>
		<tr>
			<td>Veracruz</td>
			<td>10.00</td>
		</tr>
		<tr>
			<td>Coccidial oocysts</td>
			<td>Yucat&#225;n</td>
			<td>2.30</td>
			<td>8</td>
		</tr>
		<tr>
			<td>Ctenocephalides</td>
			<td>Morelos</td>
			<td>30.3</td>
			<td>10</td>
		</tr>
		<tr>
			<td>Dipylidium caninum</td>
			<td>Yucat&#225;n</td>
			<td>2.30</td>
			<td>8</td>
		</tr>
		<tr>
			<td>Dirofilaria&#160;</td>
			<td>Yucat&#225;n</td>
			<td>7.0 &#8211; 8.3</td>
			<td>11</td>
		</tr>
		<tr>
			<td rowspan="2">Giardia</td>
			<td>Tabasco</td>
			<td>3.00</td>
			<td>6</td>
		</tr>
		<tr>
			<td>Yucat&#225;n</td>
			<td>18.8</td>
			<td>8</td>
		</tr>
		<tr>
			<td>Leishmania</td>
			<td>Chiapas</td>
			<td>19.00</td>
			<td>12</td>
		</tr>
		<tr>
			<td>Tapeworms</td>
			<td>Baja California</td>
			<td>6.79</td>
			<td>13</td>
		</tr>
		<tr>
			<td rowspan="2">Toxocara canis</td>
			<td>Quer&#233;taro</td>
			<td>22.10</td>
			<td>5</td>
		</tr>
		<tr>
			<td>Yucat&#225;n</td>
			<td>6.20</td>
			<td>8</td>
		</tr>
		<tr>
			<td>Trichuris vulpis</td>
			<td>Yucat&#225;n</td>
			<td>25.40</td>
			<td>8</td>
		</tr>
		<tr>
			<td rowspan="6">Trypanosoma</td>
			<td>Jalisco</td>
			<td>8.10</td>
			<td rowspan="6">9</td>
		</tr>
		<tr>
			<td>Campeche</td>
			<td>7.60</td>
		</tr>
		<tr>
			<td>Chiapas</td>
			<td>4.5 &#8211; 42.8</td>
		</tr>
		<tr>
			<td>Quintana Roo</td>
			<td>20.1 &#8211; 21.3</td>
		</tr>
		<tr>
			<td>Toluca</td>
			<td>17.50</td>
		</tr>
		<tr>
			<td>Yucat&#225;n</td>
			<td>9.8 &#8211; 34</td>
		</tr>
	</tbody>
</table>
Table 1: Regional prevalence (%) of dog parasites in Mexico from 2001 to 2020. Findings from previous investigations conducted from 2001 to 2020 have enabled the identification of canine parasite distribution across several urban and rural settings in Mexico. These studies provide a deep understanding of epidemiological elements conducive to the persistence of canine parasites in different ecosystems, contributing to a comprehensive assessment of the zoonotic impact of some parasite species.
Life cycle stages of intestinal parasites, such as eggs, cysts, oocysts, or larvae can be found in stool samples. Thus, examination of fecal material provides valuable information about the parasites of an animal. The need for a method to detect Ancylostomidae eggs in human feces led to the use of the simple fecal smear in 1878, which was used for many years to detect gastrointestinal parasites but was considered not very sensitive. Thus, the need arose to develop better copromicroscopic methods14. More than 100 years have passed since the flotation technique for recovering and counting parasite eggs in fecal samples was first described15. Since then, several methods and variants of the flotation technique have been considered a standard for the detection of some parasites in their hosts.
For example, Lane described a method in 1924 involving the direct centrifugal flotation technique, which integrates centrifugation followed by floating the sediment in a saturated sodium chloride solution with SpG 1.2 in 1 g (Lane) or 10 g (Stoll&#39;s modification). The flotation technique was subsequently modified by using solutions with different SpG14. In 1939, Gordon and Whitlock reported the disadvantages of Stoll&#39;s technique due to interference from detritus in visualizing parasite eggs and developed the quantitative method known as McMaster16. In 1979, O&#39;Grady and Slocombe demonstrated that the specific gravity of the solution, timing, and mesh sizes of strainers affect the accuracy of egg detection using the flotation technique17. During the last decades, because several modifications have been made to the flotation technique, there is an urgent need for standardization of flotation methods. Currently, detection of canine helminth infections in the context of prevention of zoonotic parasites is required to apply appropriate anthelmintic treatments to limit environmental contamination with infectious stages of zoonotic nematodes18.
Among qualitative methods, the fecal flotation technique is widely used and accepted because it does not require much equipment, is simple, inexpensive, and reproducible; yet it has a major drawback in that it lacks sensitivity when the intensity of the infection is low19. The ability to reveal the presence of a greater number of parasitic elements such as eggs, oocysts, cysts, or nematode larvae is usually determined by the density of the solution20.
Previous reports have compared coproparasitological techniques for the detection of canine nematode eggs. With regard to the detection of motile protozoa, direct fecal smears are used; whereas sedimentation methods are useful for diagnosing heavy eggs of parasites such as trematodes21. One of the most widely used field-based diagnostic tests is the fecal smear method. However, the low level of sensitivity of this technique may be attributed to the fact that it does contain debris that interferes with the detection of parasite eggs. By incorporating a sieving step along with solutions that provide the proper SpG, the flotation method offers a clearer and less cluttered observation of ascarid and hookworm eggs. This leads to a more precise and efficient process for microscopic screening22. Likewise, simple flotation and direct centrifugal flotation techniques are very commonly utilized to recover parasite eggs and oocysts14. The classic flotation methods can be considered qualitative or quantitative depending on the use of a counting chamber such as the McMaster method15. Nonetheless, as the flotation technique has low sensitivity and focuses on the detection of parasites in the patent period, negative results should not be considered conclusive. However, the accuracy not only depends on the preservation procedure of fecal samples or the SpG of flotation solutions but also depends on the technical proficiency and experience in conducting fecal examinations of the user.
Consequently, other methods have been explored for the detection of canine parasites in feces. It has been generally recognized that one of the most widely used approaches for the diagnosis of intestinal helminth infections in dogs is the FLOTAC technique, a multivalent, sensitive, and accurate method that yields accurate and reliable results for the diagnosis of A. caninum in dogs when compared to a flotation protocol in a tube and the McMaster technique19,23. Sedimentation methods are useful for recovering fluke eggs, embryonated nematode eggs, and most tapeworm eggs, which cannot be recovered on the surface of a flotation solution because these structures do not float24. One method that has been proven to be superior to flotation/sedimentation techniques is the Modified Double Centrifugal Flotation method, as it enables the detection of cestode eggs in feces, is less time-consuming, separates Anoplocephala eggs from fecal debris, and decreases crystallization25. Moreover, this technique has been successfully used to detect ascarid eggs with high sensitivity26. Yet, some of these aforementioned techniques and centrifugal methods such as as the Ovassay, as opposed to the flotation protocol we propose in this study, require sample preservation in reagents such as formalin, commercial kits, sample processing under laboratory conditions, and the use of reagents such as zinc sulfate27&#160;which are expensive and require special disposal procedures to avoid environmental toxicity.
The use of techniques that increase the sensitivity of the flotation method by adding solutions with high SpG has been favored recently. However, it must be considered that the disadvantage of these solutions is the increase in debris in the final preparation and hence, the inaccurate detection of parasite eggs. In addition, the commercial availability of materials, reagents, cost, environmental impact issues, and difficulty of use of centrifugal methods affect the selection of a flotation technique14, which can be challenging in field conditions in contrast to the protocol that we present in this work. The preparation of the flotation solutions with table salt is advantageous over the utilization of sugar because under field conditions, sugar attracts insects such as wasps and bees and preparations become sticky. Further, solutions such as phenol, which is added to sugar solutions to avoid stickiness, or ZnSO4are complex to properly discard according to environmental protection guidelines and cannot be disposed of in the field; unlike a table salt solution.
The goal of this manuscript is to demonstrate the steps to detect T. canis and Ancylostoma spp. eggs in fecal samples using an adaptation of the simple flotation technique under field and laboratory conditions. Following the protocol herewith described and using a microscope with a backup battery, the diagnosis of these canine zoonotic parasites in rural and suburban areas is possible when no laboratory equipment and infrastructure are available. The simple flotation method described in this work can provide quick results and is a non-invasive and cost-effective technique for routine screening.

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a simple fecal flotation method for diagnosing zoonotic nematodes under field and laboratory conditions

Diagnosis of canine parasites with zoonotic potential such as Toxocara canis and Ancylostoma caninum under field conditions is usually difficult due to limited access to a laboratory in rural and suburban areas in Mexico. This study aimed to detect T. canis and Ancylostoma spp. in fecal samples collected from dogs in Mexico from 2017 to 2021 under field conditions. Sample size calculation resulted in a target enrollment of 534 dogs across the country.
Samples were collected directly from the rectum or the ground after defecation. Samples were stored in individual, tightly sealed, plastic bags at 4 &#176;C. A saturated solution of sodium chloride (specific gravity [SpG] 1.20) was prepared both under field and laboratory conditions. Within 3 days of collection, 2-4 g of feces were tested for parasites using a flotation method by suspending each fecal sample in a saline solution. Feces were mixed with the flotation solution and crushed using a metal spoon.
Once a uniform consistency was achieved, the fecal sample was poured into a new plastic cup using a sieve and allowed to sit for 10-15 min. Three drops from the top of the mixture were collected using a sterilized inoculating loop. The slides were placed on the microscope and parasites were identified by trained parasitologists. Fecal samples from 1,055 dogs were screened microscopically. The number of positive samples for Ancylostoma spp.&#160;was 833 (78.95% frequency) and 222 (21.04%) for T. canis. These findings illustrate the importance of identifying zoonotic helminths in dogs living in urban and rural areas in Mexico using a coproparasitoscopic technique in the laboratory and under field conditions.

In this work, collection and coproparasitoscopic procedures for the identification of T. canis and Ancylostoma spp. are described. The rationale behind the adaptation of the simple fecal flotation method to detect canine helminth eggs is that this technique is cost-effective as the solutions, equipment, and materials are inexpensive. Hence, the method has a high sample handling capacity as multiple samples can be processed in a short period. Moreover, the simple fecal flotation method is easy to perform...

Watch this Scientific Journal Video about A Simple Fecal Flotation Method for Diagnosing Zoonotic Nematodes Under Field and Laboratory Conditions at JoVE.com

Author Spotlight: Coproparasitoscopic Examination of Dog Stools for Control and Prevention of Zoonotic Parasite Diseases

This work describes the use of a flotation method to identify Toxocara canis and Ancylostoma spp. detected in fecal samples collected from dogs in Mexico from 2017 to 2021 under field conditions.

A Simple Fecal Flotation Method for Diagnosing Zoonotic Nematodes Under Field and Laboratory Conditions

Diagnosis of canine parasites with zoonotic potential such as Toxocara canis and Ancylostoma caninum under field conditions is usually difficult due to ...

a-simple-fecal-flotation-method-for-diagnosing-zoonotic-nematodes

Research

JoVE Journal

Immunology and Infection

2.2K Views.  Universidad Nacional Autonoma de Mexico. Momenteel wordt een landelijke geolocatiestudie van de zoönotische parasieten van honden uitgevoerd om verdere controle- en preventiestrategieën voor deze ziekten te ontwikkelen. Het bestaan van een grote verscheidenheid aan ecosystemen in Mexico beïnvloedt de frequentie van parasitaire infecties bij honden. Daarom is het noodzakelijk om veldwerk uit te voeren en deze parasieten te identificeren om regiospecifieke ontwormingsrichtlijnen te kunnen voorstellen op basis van de epidemiologie v...

Video: Auteur in de schijnwerpers: coproparasitoscopisch onderzoek van hondenontlasting voor controle en preventie van zoönotische parasietziekten

Helminth Collection and Identification from Wildlife

Wild animals are commonly parasitized by a wide range of helminths. The four major types of helminths are &#34;roundworms&#34; (nematodes), &#34;thorny-headed worms&#34; (acanthocephalans), &#34;flukes&#34; (trematodes), and &#34;tapeworms&#34; (cestodes). The optimum method for collecting helminths is to examine a host that has been dead less than 4-6 hr since most helminths will still be alive. A thorough necropsy should be conducted and all major organs examined. Organs are washed over a 106 &#956;m sieve under running water and contents examined under a stereo microscope. All helminths are counted and a representative number are fixed (either in 70% ethanol, 10% buffered formalin, or alcohol-formalin-acetic acid). For species identification, helminths are either cleared in lactophenol (nematodes and small acanthocephalans) or stained (trematodes, cestodes, and large acanthocephalans) using Harris&#39; hematoxylin or Semichon&#39;s carmine. Helminths are keyed to species by examining different structures (e.g. male spicules in nematodes or the rostellum in cestodes). The protocols outlined here can be applied to any vertebrate animal. They require some expertise on recognizing the different organs and being able to differentiate helminths from other tissue debris or gut contents. Collection, preservation, and staining are straightforward techniques that require minimal equipment and reagents. Taxonomic identification, especially to species, can be very time consuming and might require the submission of specimens to an expert or DNA analysis.

Wild animals are commonly parasitized by a wide range of helminths.&#160; The four major types of helminths are &#8220;roundworms&#8221; (nematodes), &#8220;thorny-headed worms&#8221; (acanthocephalans), &#8220;flukes&#8221; (trematodes), and &#8220;tapeworms&#8221; (cestodes).&#160; Here we describe how helminths are collected from a vertebrate animal and how they are preserved and taxonomically identified.&#160;

Wild animals are commonly parasitized by a wide range of helminths. The four major types of helminths are &#34;roundworms&#34; (nematodes), ...

Environment

Diagnosis of Ecto- and Endoparasites in Laboratory Rats and Mice

Internal and external parasites remain a significant concern in laboratory rodent facilities, and many research facilities harbor some parasitized animals. Before embarking on an examination of animals for parasites, two things should be considered. One: what use will be made of the information collected, and two: which test is the most appropriate. Knowing that animals are parasitized may be something that the facility accepts, but there is often a need to treat animals and then to determine the efficacy of treatment. Parasites may be detected in animals through various techniques, including samples taken from live or euthanized animals. Historically, the tests with the greatest diagnostic sensitivity required euthanasia of the animal, although PCR has allowed high-sensitivity testing for several types of parasite. This article demonstrates procedures for the detection of endo- and ectoparasites in mice and rats. The same procedures are applicable to other rodents, although the species of parasites found will differ.

This article describes various procedures for screening rats and mice to detect endo- or ectoparasitism. Several diagnostic assays will be demonstrated, both those suitable for use on live animals and those used after euthanasia of the animal. Photographs to aid in identification of rat and mouse parasites will be included.

Internal and external parasites remain a significant concern in laboratory rodent facilities, and many research facilities harbor some parasitized ...

The Nematode Caenorhabditis Elegans - A Versatile In Vivo Model to Study Host-microbe Interactions

We demonstrate a method using Caenorhabditis elegans as a model host to study microbial interaction. Microbes are introduced via the diet making the intestine the primary location for disease. The nematode intestine structurally and functionally mimics mammalian intestines and is transparent making it amenable to microscopic study of colonization. Here we show that pathogens can cause disease and death. We are able to identify microbial mutants that show altered virulence. Its conserved innate response to biotic stresses makes C. elegans an excellent system to probe facets of host innate immune interactions. We show that hosts with mutations in the dual oxidase gene cannot produce reactive oxygen species and are unable to resist microbial insult. We further demonstrate the versatility of the presented survival assay by showing that it can be used to study the effects of inhibitors of microbial growth. This assay may also be used to discover fungal virulence factors as targets for the development of novel antifungal agents, as well as provide an opportunity to further uncover host-microbe interactions. The design of this assay lends itself well to high throughput whole-genome screens, while the ability to cryo-preserve worms for future use makes it a cost-effective and attractive whole animal model to study.

The Nematode Caenorhabditis Elegans - A Versatile In Vivo Model to Study Host-microbe Interactions

Here, we present the nematode Caenorhabditis elegans as a versatile host model to study microbial interaction.

We demonstrate a method using Caenorhabditis elegans as a model host to study microbial interaction. Microbes are introduced via the diet making the ...

Genetics

Determining Soil-transmitted Helminth Infection Status and Physical Fitness of School-aged Children

Soil-transmitted helminth (STH) infections are common. Indeed, more than 1 billion people are affected, mainly in the developing world where poverty prevails and hygiene behavior, water supply, and sanitation are often deficient1,2. Ascaris lumbricoides, Trichuris trichiura, and the two hookworm species, Ancylostoma duodenale and Necator americanus, are the most prevalent STHs3. The estimated global burden due to hookworm disease, ascariasis, and trichuriasis is 22.1, 10.5, and 6.4 million disability-adjusted life years (DALYs), respectively4. Furthermore, an estimated 30-100 million people are infected with Strongyloides stercoralis, the most neglected STH species of global significance which arguably also causes a considerable public health impact5,6. Multiple-species infections (i.e., different STHs harbored in a single individual) are common, and infections have been linked to lowered productivity and thus economic outlook of developing countries1,3.
For the diagnosis of common STHs, the World Health Organization (WHO) recommends the Kato-Katz technique7,8, which is a relatively straightforward method for determining the prevalence and intensity of such infections. It facilitates the detection of parasite eggs that infected subjects pass in their feces.
With regard to the diagnosis of S.stercoralis, there is currently no simple and accurate tool available. The Baermann technique is the most widely employed method for its diagnosis. The principle behind the Baermann technique is that active S.stercoralis larvae migrate out of an illuminated fresh fecal sample as the larvae are phototactic9. It requires less sophisticated laboratory materials and is less time consuming than culture and immunological methods5.
Morbidities associated with STH infections range from acute but common symptoms, such as abdominal pain, diarrhea, and pruritus, to chronic symptoms, such as anemia, under- and malnutrition, and cognitive impairment10. Since the symptoms are generally unspecific and subtle, they often go unnoticed, are considered a normal condition by affected individuals, or are treated as symptoms of other diseases that might be more common in a given setting. Hence, it is conceivable that the true burden of STH infections is underestimated by assessment tools relying on self-declared signs and symptoms as is usually the case in population-based surveys.
In the late 1980s and early 1990s, Stephenson and colleagues highlighted the possibility of STH infections lowering the physical fitness of boys aged 6-12 years11,12. This line of scientific inquiry gained new momentum recently13,14,15. The 20-meter (m) shuttle run test was developed and validated by L&eacute;ger et al.16 and is used worldwide to measure the aerobic fitness of children17. The test is easy to standardize and can be performed wherever a 20-m long and flat running course and an audio source are available, making its use attractive in resource-constrained settings13. To facilitate and standardize attempts at assessing whether STH infections have an effect on the physical fitness of school-aged children, we present methodologies that diagnose STH infections or measure physical fitness that are simple to execute and yet, provide accurate and reproducible outcomes. This will help to generate new evidence regarding the health impact of STH infections.

Chronic infection with soil-transmitted helminths (STHs) causes malabsorption, stunting, and wasting in the growing child. Hence, it is plausible that these infections also reduce the physical fitness of children. Here, we visualize two techniques for the diagnosis of STHs and the 20-meter shuttle run test for assessing children's physical fitness.

Soil-transmitted helminth (STH) infections are common. Indeed, more than 1 billion people are affected, mainly in the developing world where poverty ...

Rapid Isolation of Wild Nematodes by Baermann Funnel

Beyond being robust experimental model organisms, Caenorhabditis elegans and its relatives are also real animals that live in nature. Studies of wild nematodes in their natural environments are valuable for understanding many aspects of biology, including the selective regimes in which distinctive genomic and phenotypic characters evolve, the genetic basis for complex trait variation, and the natural genetic diversity fundamental to all animal populations. This manuscript describes a simple and efficient method for extracting nematodes from their natural substrates, including rotting fruits, flowers, fungi, leaf litter, and soil. The Baermann funnel method, a classical nematology technique, selectively isolates active nematodes from their substrates. Because it recovers nearly all active worms from the sample, the Baermann funnel technique allows for the recovery of rare and slow-growing genotypes that co-occur with abundant and fast-growing genotypes, which might be missed in extraction methods that involve multiple generations of reproduction. The technique is also well suited to addressing metagenetic, population-genetic, and ecological questions. It captures the entire population in a sample simultaneously, allowing an unbiased view of the natural distribution of ages, sexes, and genotypes. The protocol allows for deployment at scale in the field, rapidly converting substrates into worm plates, and the authors have validated it through fieldwork on multiple continents.

This protocol outlines a method for efficiently extracting live nematodes from natural substrates in the field.

Beyond being robust experimental model organisms, Caenorhabditis elegans and its relatives are also real animals that live in nature. Studies of wild ...

Visualizing Bacteria in Nematodes using Fluorescent Microscopy

Symbioses, the living together of two or more organisms, are widespread throughout all kingdoms of life. As two of the most ubiquitous organisms on earth, nematodes and bacteria form a wide array of symbiotic associations that range from beneficial to pathogenic 1-3. One such association is the mutually beneficial relationship between Xenorhabdus bacteria and Steinernema nematodes, which has emerged as a model system of symbiosis 4. Steinernema nematodes are entomopathogenic, using their bacterial symbiont to kill insects 5. For transmission between insect hosts, the bacteria colonize the intestine of the nematode's infective juvenile stage 6-8. Recently, several other nematode species have been shown to utilize bacteria to kill insects 9-13, and investigations have begun examining the interactions between the nematodes and bacteria in these systems 9.
We describe a method for visualization of a bacterial symbiont within or on a nematode host, taking advantage of the optical transparency of nematodes when viewed by microscopy. The bacteria are engineered to express a fluorescent protein, allowing their visualization by fluorescence microscopy. Many plasmids are available that carry genes encoding proteins that fluoresce at different wavelengths (i.e. green or red), and conjugation of plasmids from a donor Escherichia coli strain into a recipient bacterial symbiont is successful for a broad range of bacteria. The methods described were developed to investigate the association between Steinernema carpocapsae and Xenorhabdus nematophila 14. Similar methods have been used to investigate other nematode-bacterium associations 9,15-18and the approach therefore is generally applicable.
The method allows characterization of bacterial presence and localization within nematodes at different stages of development, providing insights into the nature of the association and the process of colonization 14,16,19. Microscopic analysis reveals both colonization frequency within a population and localization of bacteria to host tissues 14,16,19-21. This is an advantage over other methods of monitoring bacteria within nematode populations, such as sonication 22or grinding 23, which can provide average levels of colonization, but may not, for example, discriminate populations with a high frequency of low symbiont loads from populations with a low frequency of high symbiont loads. Discriminating the frequency and load of colonizing bacteria can be especially important when screening or characterizing bacterial mutants for colonization phenotypes 21,24. Indeed, fluorescence microscopy has been used in high throughput screening of bacterial mutants for defects in colonization 17,18, and is less laborious than other methods, including sonication 22,25-27and individual nematode dissection 28,29.

To study the mutualism between Xenorhabdus bacteria and Steinernema nematodes, methods were developed to monitor bacterial presence and location within nematodes. The experimental approach, which can be applied to other systems, entails engineering bacteria to express the green fluorescent protein and visualizing, using fluorescence microscopy bacteria within the transparent nematode.

 
Symbioses, the living together of two or more organisms, are widespread throughout all kingdoms of life. As two of the most ubiquitous organisms on ...

Biology

RNA Fluorescence in situ Hybridization (FISH) to Visualize Microbial Colonization and Infection in Caenorhabditis elegans Intestines

The intestines of wild Caenorhabditis nematodes are inhabited by a variety of microorganisms, including gut microbiome bacteria and pathogens, such as microsporidia and viruses. Because of the similarities between Caenorhabditis elegans and mammalian intestinal cells, as well as the power of the C. elegans system, this host has emerged as a model system to study host intestine-microbe interactions in vivo. While it is possible to observe some aspects of these interactions with bright-field microscopy, it is difficult to accurately classify microbes and characterize the extent of colonization or infection without more precise tools. RNA fluorescence in situ hybridization (FISH) can be used as a tool to identify and visualize microbes in nematodes from the wild or to experimentally characterize and quantify infection in nematodes infected with microbes in the lab. FISH probes, labeling the highly abundant small subunit ribosomal RNA, produce a bright signal for bacteria and microsporidian cells. Probes designed to target conserved regions of ribosomal RNA common to many species can detect a broad range of microbes, whereas targeting divergent regions of the ribosomal RNA is useful for narrower detection. Similarly, probes can be designed to label viral RNA. A protocol for RNA FISH staining with either paraformaldehyde (PFA) or acetone fixation is presented. PFA fixation is ideal for nematodes associated with bacteria, microsporidia, and viruses, whereas acetone fixation is necessary for the visualization of microsporida spores. Animals were first washed and fixed in paraformaldehyde or acetone. After fixation, FISH probes were incubated with samples to allow for the hybridization of probes to the desired target. The animals were again washed and then examined on microscope slides or using automated approaches. Overall, this FISH protocol enables detection, identification, and quantification of the microbes that inhabit the C. elegans intestine, including microbes for which there are no genetic tools available.

RNA Fluorescence in situ Hybridization FISH to Visualize Microbial Colonization and Infection in Caenorhabditis elegans Intestines

Intestinal microbes, including extracellular bacteria and intracellular pathogens like the Orsay virus and microsporidia (fungi), are often associated with wild Caenorhabditis nematodes. This article presents a protocol for detecting and quantifying microbes that colonize and/or infect C. elegans nematodes, and for measuring pathogen load after controlled infections in the lab.

The intestines of wild Caenorhabditis nematodes are inhabited by a variety of microorganisms, including gut microbiome bacteria and pathogens, such as ...

Environmental Screening of Aeromonas hydrophila, Mycobacterium spp., and Pseudocapillaria tomentosa in Zebrafish Systems

Health monitoring systems are developed and used in zebrafish research facilities because pathogens of Danio rerio such as Aeromonas hydrophila, Mycobacterium spp., and Pseudocapillaria tomentosa have the potential to impair animal welfare and research. The fish are typically analyzed post mortem to detect microbes. The use of sentinels is a suggested way to improve the sensitivity of the surveillance and to reduce the number of animals to sample. The setting of a pre-filtration sentinel tank out of a recirculating system is described. The technique is developed to prevent water pollution and to represent the fish population by a careful selection of age, gender, and strains. In order to use the minimum number of animals, techniques to screen the environment are also detailed. Polymerase Chain Reaction (PCR) on surface sump swabs is used to significantly improve the detection of some prevalent and pathogenic mycobacterial species such as Mycobacterium fortuitum, Mycobacterium haemophilum, and Mycobacterium chelonae. Another environmental method consists of processing the sludge at the bottom of a holding tank or sump to look for P. tomentosa eggs. This is a cheap and fast technique that can be applied in quarantine where a breeding device is submerged into the holding tank of imported animals. Finally, PCR is applied to the sludge sample and A. hydrophila is detected at the sump&#39;s bottom and surface. Generally, these environmental screening techniques applied to these specific pathogens have led to an increased sensitivity compared to the testing of pre-filtration sentinels.

Environmental Screening of Aeromonas hydrophila, Mycobacterium spp., and Pseudocapillaria tomentosa in Zebrafish Systems

This protocol describes the use of sump swabs and sludge analysis of zebrafish systems, which leads to increased detection compared to the sole use of sentinels to detect pathogens such as Aeromonas hydrophila, Mycobacterium spp., and Pseudocapillaria tomentosa. A system to monitor P. tomentosa eggs in quarantine is also proposed.

Health monitoring systems are developed and used in zebrafish research facilities because pathogens of Danio rerio such as Aeromonas hydrophila, ...

High-throughput Measurement of Gut Transit Time Using Larval Zebrafish

Zebrafish are used as alternative model organisms for drug safety testing. The gastrointestinal (GI) tract of zebrafish has genetic, neuronal, and pharmacological similarities to that of the mammals. GI intolerance during clinical testing of drug candidates is common and may pose a serious threat to human health. Testing for GI toxicity in preclinical mammalian models can be expensive in terms of time, test compound, and labor. The high-throughput method presented here may be used to predict GI safety issues. Compared to mammalian models, this method allows for more expedient assessment of test compound effects on GI transit while using low quantities of compound. In this method, larval zebrafish (7 days post fertilization) are fed food containing a fluorescent label. After feeding, each larval fish is placed into a well of a 96-conical-bottom-well plate and dosed with test compound (dissolved in water) or the vehicle. As gut transit occurs, fecal matter accumulates on the bottom of the wells, and the rate at which this happens is monitored by measuring fluorescence from the bottom of the well repeatedly over time using a plate spectrophotometer. The fluorescence from larvae in a given treatment group are averaged and these values are graphed along with standard error, for each measurement time, yielding a curve representing average transit of food over time. Effects on gut transit time are identified by comparing the area under the curve for each treatment group to that of the vehicle-treated group. This method detected changes in zebrafish GI transit time induced by drugs with known clinical GI effects; it can be employed to interrogate dozens of treatments for GI effects per day. As such, safer compounds can be quickly prioritized for mammalian testing, which expedites discovery and proffers 3Rs advancement.

The goal of this protocol is to measure the transit time of fluorescently labeled food through the gut of larval zebrafish in a high throughput fashion.

Zebrafish are used as alternative model organisms for drug safety testing. The gastrointestinal (GI) tract of zebrafish has genetic, neuronal, and ...

A Highly Scalable Approach to Perform Ecological Surveys of Selfing Caenorhabditis Nematodes

Caenorhabditis elegans is one of the major model organisms in biology, but only recently have researchers focused on its natural ecology. The relative sparsity of information about C. elegans in its natural context comes from the challenges involved in the identification of the small nematode in nature. Despite these challenges, an increasing focus on the ecology of C. elegans has caused a wealth of new information regarding its life outside of the laboratory. The intensified search for C. elegans in nature has contributed to the discovery of many new Caenorhabditis species and revealed that congeneric nematodes frequently cohabitate in the wild, where they feed on microbial blooms associated with rotting plant material. The identification of new species has also revealed that the androdioecious mating system of males and self-fertilizing hermaphrodites has evolved three times independently within Caenorhabditis. The other two selfing species, C. briggsae and C. tropicalis, share the experimental advantages of C. elegans and have enabled comparative studies into the mechanistic basis of important traits, including self-fertilization. Despite these advances, much remains to be learned about the ecology and natural diversity of these important species. For example, we still lack functional information for many of their genes, which might only be attained through an understanding of their natural ecology. To facilitate ecological research of selfing Caenorhabditis nematodes, we developed a highly scalable method to collect nematodes from the wild. Our method makes use of mobile data collection platforms, cloud-based databases, and the R software environment to enhance researchers&#39; ability to collect nematodes from the wild, record associated ecological data, and identify wild nematodes using molecular barcodes.

A Highly Scalable Approach to Perform Ecological Surveys of Selfing Caenorhabditis Nematodes

This protocol can be used to perform large-scale ecological surveys of selfing Caenorhabditis nematodes. The primary advantage of this method is the efficient organization and analysis of ecological and molecular data associated with the nematodes collected from nature.

Caenorhabditis elegans is one of the major model organisms in biology, but only recently have researchers focused on its natural ecology. The relative ...

A Simple Fecal Flotation Method for Diagnosing Zoonotic Nematodes Under Field and Laboratory Conditions

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