Parasites effect a vast number of the world’s population, and they are seen as directly decreasing the productivity of people, and increasing the morbidity/mortality of affected persons. I have witnessed numerous children afflicted with taeniasis (tapeworm), ascariasis (roundworm), and giardiasis while on a medical mission trip to a remote region in Peru. The burden of parasitic infections in these children was immense and contributed to stunted growth, fatigue, and likely cognitive delays. Though in North America we typically do not worry about parasitic diseases, this is only a recent phenomenon that has occurred in the past 60 to 80 years. Parasites still do exist in the U.S. and they are still significant enough of a threat that the Centers for Disease Control (CDC) collects data/asks for mandatory reporting for many parasitic infections. As such, parasitic diseases should be part of everyone’s medical threat assessment.
Parasitic diseases once believed to be suppressed or on the verge of eradication seem to be re-emerging over the past several decades, this is attributable in part, to increased world travel, declining living/hygiene standards, deteriorating infrastructure, increasing population densities of cities, and an increased resistance to treatment/preventative measures (i.e. malaria). Though this article does not delve into all parasitic diseases, it does delve into the more common and some of the more potentially serious parasitic diseases. It will specifically look at those diseases that have a higher likelihood of affecting individuals living in the U.S. This includes those parasites that are considered eradicated/have a minimal disease burden, but that may once again cause issues due to a lack of preventative measures, or a failure of the health-care system in stemming an outbreak. Prevention, parasitic identification methods (clinical, basic microscopy), and treatment will be discussed for informational purposes only. Any epidemiological statistics/historical information presented in this article are taken from the CDC web site and are in the public domain. Methods on obtaining specimens and slide preparation/staining techniques are summarized from the book “Medical parasitology, a self instructional Text” by Leventhal and Cheadle. The full reference is available at the end of this article.
In the interest of full disclosure I am a health care provider with training in parasitology to include the basic microscopy methods and various treatment modalities mentioned in this article. If you are experiencing any of the below mentioned symptoms, or suspect that you or another individual has a parasitic infection you should discuss any diagnostic testing and possible treatment plans with a trained and licensed medical provider. If you are interested in the study of parasites I recommend a course at a local university that also has a laboratory/practical component where you can better learn to identify parasites and become proficient in specimen staining/slide specimen preparation techniques that are beyond the scope of this article. I strongly encourage the use of proper personal protective equipment when dealing with suspected parasites, and certainly when dealing with bodily fluids to include gloves, gown/lab coat. Hand hygiene should always be performed after handling specimens.
Parasitic Intestinal Infections
Intestinal Protozoal Infections
Some of the more common parasites affecting the intestines belong to a type of organism classified as protozoa. Protozoa are large single celled organisms with cellular machinery much like our own human cells and are unlike any type of bacteria. The first protozoan to be discussed is Entamoeba histolytica, which causes amoebic dysentery (bloody diarrhea). This organism has a worldwide distribution though it is more common in Central/South America, Africa, and developing portions of Asia (though I have seen it occur from drinking contaminated stream water/handling contaminated food in the U.S.). Infections occur with the ingestion of contaminated (with fecal matter) food or water. Symptoms may include bloody diarrhea, diarrhea without blood, weight loss, possible fever, and generalized versus right upper quadrant abdominal pain (indicating possible liver involvement). Patients many times present with a history of diarrhea that has been ongoing for a week or longer, and have a history of traveling to areas that are known to have an increased incidence of infections, or possibly drinking untreated water while hiking. Treatment other than rehydration therapy may be started empirically if the patient has dysentery/inflammatory diarrhea (bloody diarrhea with abdominal pain). I would begin empirical treatment with an anti-protozoal/clostridium difficile agent such as metronidazole. Also, if treating empirically for inflammatory diarrhea (bloody diarrhea), it would be advisable to also give ciprofloxacin to treat for any type of pathogenic e-coli strains or salmonella. The differential diagnosis considerations are vast and beyond the scope of this article, but would include: Diverticulitis, ulcerative colitis, other infectious diarrheal organism, and cancer. If a compound light microscope with an oil immersion lens (up to at least 900 power) was available you would have the potential to perform an iodine stain of a stool sample and prepare a “wet mount” of fresh fecal matter to examine a patient’s feces for any evidence of a protozoal infection.
Preparing a “wet mount” and Iodine staining procedure:
1. Add 1 gram potassium iodine and 1.5 grams powdered iodine crystals to 100mL of distilled water and shake vigorously until dissolved in solution. Conversely, you can also purchase Lugol’s iodine stain from a veterinary supplier.
2. Using an applicator stick mix a small amount of feces with a drop of saline solution on a microscope slide and apply a cover slip over it. The specimen/fluid should not run out from under the cover-slip and should be opaque enough to see through it.
3. Systematically examine the slide moving from low power to a high power oil immersion lens (using mineral oil) and pay particular attention for any movement from flagellates/amoeba. Ensure that your light source is dim enough for you to discern any movement and to not wash out your field of view as there is little contrast in an unstained/saline only slide.
4. Prepare another slide and instead of using saline add a small drop of your prepared iodine solution. Again systematically examine the slide moving from low power to a high power oil immersion lens .
If Entamoeba histolytica is present you may see movement on the saline slide (as with many protozoal infections). However, if it the amoeba is present on the slide prepared with the iodine stain then you are likely not to see any movement as the iodine will kill the protozoan, but you will see larger spherical to oval shaped objects typically with greater than 3-4 nucleii readily identifiable and asymmetric in appearance (smaller/darker spheres contained within the larger spherical/oval shape).
Another intestinal protozoan known as Giardia lamblia causes what is known as “traveler’s diarrhea” and is colloquially known as “Montezuma’s revenge.” This parasite is one of the most common parasitic infections in North America. It is found world-wide and is again more prevalent in developing countries. It is spread via the fecal oral route by contaminated food/water and is endemic to numerous mammals in North America. Hence, drinking untreated fresh water places you at risk for developing giardiasis. Interestingly, in 2010 the CDC reported that the highest incidence of infection occurred in Vermont and not in any of the southern border states. Generally, patients presenting with giardiasis complain of sudden onset of diarrhea that is initially watery, without any mucous/gross blood. They may describe their stools as greasy and extremely foul smelling. The patient also commonly complains of belching (burping) a sulfuric smell, and extraordinary foul smelling flatus (farts) as well as abdominal bloating and cramping. The patient commonly states that symptoms worsen after they eat. Patients may also have a history of traveling to areas that are known to be higher risk, or possibly drinking untreated fresh water. Generally the diarrhea can be quite debilitating and may require oral and even IV rehydration therapy. Many times individuals can recover from giardiasis with oral rehydration therapy and develop subsequent resistance to this parasite. However, if a patient presented with the above symptoms, I would recommend empiric treatment with the anti-protozoal agent metronidazole as there are risks of developing complications secondary to the infection. Also, the risk of others becoming incapacitated with giardiasis that live in close proximity to an infected patient is very high. Though the differential diagnoses again are numerous, in my experience giardiasis generally presents as rather clear cut. Patients typically present nearly textbook with the above symptoms and usually have a history of traveling to a high risk area.
A compound light microscope can again be used to help identify if Giardia lamblia is present in a patient’s stool using the procedure listed above to include performing wet mounts with both saline and iodine staining solution. Typically, with a saline wet mount using high power (oil immersion microscope lens) the organism is easily identifiable by how it moves as it is a flagellate. It’s movement is best described as moving like a “falling leaf” on the slide. When viewing the specimen that is stained with iodine typically the nucleii are readily apparent and the parasite has either a tear drop shape with an appearance like that of an owl’s face (the nucleii being the eyes), or it is oval with 2 sets of nucleii (total of 4) that that are symmetrical. In both cases the nucleii look like symmetrical pairs of eyes staring back at you.
Intestinal Worm Infections
There are numerous types of intestinal worm infections. However, only the most common ones/higher potential to be seen in North America will be discussed. They include: Taenia Solium (pork tapeworm)/Taenia Saginata (beef tapeworm), Enterobius vermicularis (pin worm), Necator americanus (Hook worm), and Ascaris lumbricoides (roundworm). Tapeworms, namely the pork and beef tapeworm were estimated to have affected 100,000 people in N. America in the 1950’s. In some places in the world over 50% of the population is infected. They can grow up to 7 meters in length and have up to 100 segments with each segment producing up to 50K eggs. Tapeworms are typically spread by the ingestion of undercooked pork or beef that contains cysts/eggs of the parasite. They can also be spread by fecal-oral transmission. It is noted that tapeworm eggs are sticky and tend to cling under fingernails and are easily transferred to food. Tapeworms in humans usually affect the gut, but tapeworm larvae can migrate to muscle tissue, brain tissue, organ tissues. Larvae migrating to tissues other than the intestines can be devastating (can be a secondary cause of epilepsy/seizures). Most individuals with intestinal tapeworm infections are asymptomatic and have vague intestinal symptoms (such as nausea, hunger pain, a sensation of movement in their abdomen, loss of appetite, weight loss, bloating). The most common factor leading to individuals coming in for an exam is seeing/finding worms in their stool or feeling the movement of worms in the anus.
On presentation a patient may also have a history of traveling to areas that are known to be higher risk and/or they may live in close proximity to livestock. They may also have a history of eating undercooked beef or pork. If a patient is presenting with a report of finding worm segments in his/her stool one should be prepared to perform a gross examination of the patient’s feces. The surface should be examined first for any worm segments. The stool should be broken up to ensure no segments are present. If any worm segments are detected treatment should be started. A compound light microscope can again be used to help identify if Taenia saginata/solium is present in a patient’s stool using the procedure listed above to include performing wet mounts with both saline and iodine staining solution. Tapeworm eggs are spherical and are difficult to discern as eggs at low power. However, at higher power there is a thick outer shell that is yellowish in coloration with radial striations pointing outwards. One may see hooklets in the center of the egg from the scolex that the tapeworm uses to attach to the intestinal lining. Treatment for intestinal infections only is accomplished with praziquantel. If infections are present in the liver albendazole may also be used. Infections from larvae that have migrated outside of the GI tract will likely require additional treatment modalities not discussed here.
Pin worm (Enterobius vermicularis) infection is one of the most common worm infections in the U.S. Most individuals infected are largely asymptomatic, which is one reason it is so common. The CDC recently estimated that approximately 40 million individuals are infected in the U.S. alone. This parasites’ distribution is again worldwide and is most common in children and those living in institutional type settings. Transmission occurs person to person via fecal-oral contamination. It is important to note that eggs can remain dormant for several weeks once outside of the body and are also noted to easily stick under fingernails. Symptoms, if any are present include intense itching of the area around the rectum (pathognomonic for pinworms) occurring especially at night when the worms exit the rectum to lay eggs. Each female worm can produce up to 15K eggs. Other symptoms may include abdominal pain and mild inflammation and redness around the rectum without any evidence of inflammation of the colon. Occasionally pinworms may be seen with an examination when the worms exit the rectum to lay eggs, or rarely seeing pinworms in the stool itself. Complications arising from pinworm infections are rare. Pinworm infections are self limiting, but as auto-reinfection is so easily possible, and the risk to spreading to others is so great I would recommend treating the individual and all household contacts. Treatment consists of mebendazole or albendazole with repeat treatment in two weeks after hygiene measures have been instituted (laundering undergarments, bedding, and trimming nails). Diagnosis is easily performed with the use of cellophane tape, a tongue depressor, and a compound light microscope.
Cellophane tape test performed in the morning prior to showering/having bowel movement
1. Take a piece of cellophane tape and attach it to both sides of a wooden tongue depressor with the tape wrap around the top of the depressor. The sticky side should face outwards. The length of the piece of tape should allow you to apply the sticky side along the entire area of the rectal mucosa.
2. The Buttocks should be spread outwards, and the taped end of the tongue depressor should be applied to the rectal mucosa and touching either side of the buttocks.
3. The tape should be removed and applied sticky side down to a glass slide. Systematically examine the slide moving from low power to higher power (an oil immersion lens is not required). Ensure that your light source is dim enough for you to discern any worm eggs and not wash out your field of view.
Pinworm eggs can be seen with as little magnification as 100x. They appear oblong/oval shaped, and they have a distinct line down the middle almost making the eggs appear like a hotdog bun.
Hookworm (Necator americanus) infections were at one time almost synonymous with living in the Southern states; though infections in North America are exceedingly rare today. That being said the civilian public health service was still building outhouses in the Southern U.S. to help eliminate hookworm infections up to 1947. Hookworm infections can cause intellectual and growth retardation in children, as well as anemia and fatigue. Numerous historians credit epidemic hookworm infections in the Confederate army as aiding the Union in winning the civil war. Many Confederate soldiers suffered from anemia due to hookworm infections as well as sores on their feet from where the parasite penetrated the skin. Hookworm eggs are released in the feces of an infected individual and the egg hatches in 1-2 days. After hatching the larvae penetrates the skin of humans (typically the feet) and then travels to the lungs via the blood stream where it is coughed up, swallowed, and matures in the intestine while feeding on the host’s blood. Patients may present with complaints of itching at the site of skin penetration by the larvae. A subsequent raised and creeping reddish/inflamed track line (typically on feet) that itches profusely may appear and is known as cutaneous larva migrans. However, it should be noted in the U.S. today anyone presenting with cutaneous larva migrans is typically treated for a type of hookworm (affects dogs/cats) that is not pathogenic to humans (humans are not the definitive host). Hence, the hookworm dies while attempting to travel in the cutaneous tissues. The treatment is the same for any species of hookworm (pathogenic to humans or not). Depending on where the infection is progressing the patient may also have a cough, wheezing, gastric pain, anemia, easy fatigability, diarrhea, and/or anorexia. A compound light microscope can again be used to help identify if hookworm eggs are present in a patient’s stool using the procedure listed previously to include performing wet mounts with both saline and iodine staining solution. Hookworm eggs are oval/oblong, and they have a very thin outer shell that is clearly visible without higher magnification requiring an oil immersion lens. Eggs can contain larvae or 4-8 cell stage embryos. Treatment consists of mebendazole or albendazole.
Ascaris lumbricoides (roundworms) infections were once commonplace in the South Eastern U.S. and as recently at the 1980s it was reported that up to 32% of school children in certain areas in Florida were infected with this parasite. Also, of note numerous species of roundworms exist that affect cats/dogs and are also pathogenic to humans. Cold and dry climates are typically free of high rates of infection. A single adult female worm has been known to produce up to 250,000 eggs per day in a host’s intestine. The eggs are extremely robust and are even known to be resistant to formaldehyde and can remain infective in the soil for several years. Ascariasis infections are common in the developing countries of Asia (extremely prevalent in China), Africa and Latin America. Transmission occurs from fecal oral contact. Once eggs that have been shed in feces are ingested they hatch in the intestine and travel to the lungs via the blood stream where the larvae are coughed up, swallowed, and mature in the intestine. Most patients with roundworm infections are asymptomatic. However, patients may experience respiratory symptoms (fever, cough, wheezing) as the worms migrate to the lungs. Also, vomiting and abdominal pain, nausea, chronic diarrhea may occur after the parasite has traveled to the intestine. In children that are infected, one may see delayed developmental milestones, evidence of iron deficiency anemia, or evidence of a protein deficiency. The most common potential severe complication from a roundworm infection is a bowel obstruction. There are reports of Worms (up to 1ft long) at times seen exiting the nose/mouth/rectum spontaneously. There are also reports exist of worms exiting a host if a patient is suffering from a high fever, or he/she has been placed under general anesthesia. A compound light microscope can again be used to help identify if roundworm eggs are present in a patient’s stool using the procedure listed previously to include performing wet mounts with both saline and iodine staining solution. Ascaris eggs are typically spherical/to slightly oval in appearance. In viewing the egg, they are noted to have a thin outer though very distinct coat that is not uniform in appearance circumferentially. Also there is a clear space between the outer coat and a thick inner coat that is described as a yellow brown shell. The eggs can be viewed without higher magnification requiring an oil immersion lens. Treatment should be initiated if the parasite is found in feces using microscopy, or if the adult worm is seen exiting the anus/nose/mouth. Treatment consists of either albendazole, mebendazole, or ivermectin.
Blood Parasites (Malaria)
One of the most common parasitic infections in the world is malaria. Malaria is caused by a group of protozoal organisms that invade red blood cells. There are five different species that cause malaria. The most deadly is Plasmodium falciparum, which is endemic to the tropical regions of southeast Asia, Africa, and South America. The most widely disseminated parasite that causes malaria is Plasmodium vivax as it is found in the Americas, Eastern Europe, Asia, and North Africa. Plasmodium vivax can and does exist in more temperate climates. Worldwide, malaria causes approximately 500,000 deaths per year (typically children/pregnant women). Malaria, was once common in the U.S. up until the early 20th century with a range extending throughout the Midwest, South, and the eastern seaboard up to New England. Malaria was considered eradicated in the U.S. in the 1940s due to a concerted public health effort, and with the widespread use of the pesticide DDT. However, it should be noted that the CDC states approximately 15,000 malaria cases were still reported in the U.S. in 1947, and even though malaria is currently considered eradicated in the U.S. up to 1,500 cases are reported annually. These malaria cases typically occur from travelers returning from high risk areas. As such, there is a risk that epidemic malaria can again occur in the U.S. One only has to look at news reports about Greece to see how rapidly it can recur when the public health system stops employing preventative measures.
Malaria transmission occurs from a person being bitten by a female mosquito (specifically of the genus Anopheles) that is infected with the parasite causing malaria. Within 1-2 weeks after being bitten by an Anopheles mosquito the parasites have multiplied in the liver and they begin to invade red blood cells. After invading the red blood cells the parasites replicate, and in a synchronized fashion burst open the red blood cells and invade other red blood cells. This synchronous bursting of red blood cells causes the “cyclic” fevers that malaria is known for. In fact one can typically state the species type based on the length of time it is from one fever to the next. Over time Plasmodium falciprum causes fevers every 36 to 48 hrs and Plasmodium vivax causes fevers every 48 hrs. Symptoms of a malaria infection include high fevers that become more cyclic over time (as described above),an enlarged spleen (over time), headaches, pain in the muscles and joints, and anemia. If infected with the most virulent form of malaria (Plasmodium falciparum) one may also experience bloody urine, and seizures. Diagnosis is based on microscopy and the use of more complex slide preparation (blood smears)/staining procedures not discussed in this article. However, medication prophylaxis is recommended for individuals traveling to high risk areas. Malaria prophylaxis consists of the daily use of doxycycline two days prior to travel and for up to 30 days upon return. Also, one’s healthcare provider may consider the use of the medication primaquine as an adjunct to take along with doxycycline .
There are numerous types of parasitic arthropod (insect) infections. However, only three of the most common will be discussed in this article and include: Pediculus humanus (head/body louse), Sarcoptes scabiei (scabies), and ticks (numerous species). Pediculus Humanus (head/body louse) is epidemic in the U.S. and several million cases are reported annually. Head/body lice are thin and approx only several millimeters in size with a head, body, thorax, and 6 legs. Eggs are deposited at the base of hair shafts. Transmission is from direct contact with an infected individual (most commonly direct head to head contact). Significant complications associated with infected individuals are limited to secondary bacterial infections from itching, and the potential for contracting typhus (a potentially deadly illness). Though typhus is not currently a concern in the U.S. it has the potential to again re-appear. Itching associated with lice infections is caused by the saliva and fecal excretions of the parasite irritating the skin. Direct visualization of the parasite leads to the diagnosis as they are visible with the naked eye during a careful examination. Treatment consists of the use of topical permethrin, or malathion. Other treatment methods include using a fine toothed special metal lice comb and combing wet hair vigorously daily. Also, petroleum jelly is thought to cause suffocation of the parasites and should be massaged in and left overnight. After washing out the petroleum jelly, nit picking using a fine toothed comb aids in preventing re-infestation from already deposited eggs.
Sarcoptes scabeiei (scabies) is a microscopic mite that burrows under the skin and spreads very rapidly. Transmission is from direct contact with an infected individual and occurs most often in institutional environments/close crowding of individuals. Symptoms include intense itching that seems to worsen at night/with hot showers. Typically one will see a short red/inflamed burrow/tract that is up to several centimeters in length. A purple/blue surgical marker can be used to color over any itchy/excoriated areas on the patient and then wiped off gently with an alcohol swab. If a linear burrow is revealed one may conclude that a scabies infection is likely. The parasite typically favors areas that are cooler, i.e. along the knuckles, penis. A person’s face is typically not affected. Potential complications include secondary bacterial infections from itching, or even prolonged itching even after treatment. Treatment consists of either using topical permethrin (from the neck line down ) prior to sleep and washing off in the morning, or alternatively oral ivermectin. Treatment should be afforded to close contacts even if they are not symptomatic. Also, all bedding/clothing should be washed to prevent a possible re-infection. Oral steroids/antihistamines should be considered if itching is severe.
Numerous species of ticks are endemic to the U.S. that can carry bacterial, rickettsial (bacterial organism that can only grow inside other cells), viral, and protozoal organisms that may be transmitted when the tick is feeding. Some of the more common Tick born diseases include: Lyme disease, tularemia, Rocky Mountain spotted fever, Colorado tick fever, and anaplasmosis. There is no scarcity of information about these organisms on the web/CDC web site, and it is beyond the scope of this article to discuss them in detail. Ticks are present throughout the U.S. and typically larger juveniles/adults will climb up on blades of grass or leaves and seek a larger host (by heat, vibration, odor, etc.). One should note that ticks that are searching for a host are typically found in greater numbers at the edge of clearings (where the light meets the shade) and where higher humidity is present. Anytime one has been out in the wilderness one should perform a tick inspection (to include difficult to see areas using a mirror). Ticks should be removed as soon as they are discovered to decrease the risk of acquiring a tick-borne illness. For example, a tick carrying lyme disease needs to be attached for greater than 24-hrs to transmit the disease to a human host. Removal of ticks consists of mechanically removing the tick using fine tipped tweezers/forceps and grasping as close to the skin as possible to ensure that the entire tick is removed without leaving the head in place. Also, one must take care not to crush the tick during removal. The area where the tick was attached should be thoroughly cleaned/disinfected after tick removal. Great importance should be placed on personal prevention in areas that have the potential to harbor high tick populations. Preventative measures include pre-treatment of clothing with permethrin, use of insect repellant with at least 20% DEET, proper blousing of clothing, and regular inspections for ticks on one’s body.
Individuals as well as localities should incorporate education about parasites and discussions on what they can do as individuals/groups to better prevent parasitic infections. Even though many preventative measures are commonsense, discussions should include abstaining from using night soil (human excrement) as fertilizer, and using proper latrines/disposing of human waste appropriately. Also, ensuring that the water supply is filtered/treated properly is of key importance as is appropriate hand hygiene. In malaria prone areas prophylactic medication should be taken as directed and permethrin impregnated mosquito nets should be used as well as permethrin impregnated clothing and insect repellent with at least 20% DEET. If at all possible stagnant/sitting bodies of water should be drained in malaria prone areas to help decrease the mosquito population. Lastly, routine health inspections should be considered in populations living in close quarters/more of an institutional type of setting.
I hope that this article has been informative to you the reader, and that at the very least you have a greater appreciation for the risks presented by parasitic infections. I would again urge the reader to consider a formal class in parasitology, or at the very least to review the reference materials listed below to be better armed with knowledge in understanding, preventing, identifying, and treating parasitic infections.
1. The Centers for Disease Control (CDC) web site (viewed at www.cdc.gov ) has a wealth of knowledge relating to parasites in the U.S. and Worldwide. This includes current and historical information about prevalence of said diseases, treatment, and preventative measures.
-Specifically, I would recommend reading the following resources from the CDC:
2. If you are interested in adding to your medical library regarding parasitic infections I would recommend the text “Medical parasitology. A self instructional text” (5th Ed) by Leventhal and Cheadle. It is a very inexpensive easy to read reference textbook.
3. Army field manuals/publications also afford pragmatic advice, and easily readable information pertaining to prevention/sanitation.
– I would recommend reading the following resources