Parasites are organisms that live on or in a host organism and get their food from or at the expense of the host. There are many different types of parasites, ranging from tiny microorganisms to larger organisms like worms or arthropods. Parasites can infect humans as well as animals.
When a parasite infects a host, it often causes some level of damage as it steals nutrients and energy from the host. This can result in symptoms that may seem minor at first but can become more severe if the infection grows unchecked. Recognizing the common locations where parasitic infections first produce symptoms can help identify the type of parasite and guide treatment approaches.
Skin
One of the most obvious places people may first feel parasites is in or on the skin. Skin parasites may cause itching, rashes, lesions, or other irritation. Some examples of skin parasites include:
– Scabies mites: These tiny mites burrow into the skin and cause intense itching, often worse at night. A rash of small, red bumps or threads under the skin often occurs where the mites have burrowed. Scabies is very contagious and spreads quickly through skin-to-skin contact.
– Ringworm fungi: Contrary to the name, ringworm is not caused by a worm at all. It is a contagious fungal infection that can infect the top layer of skin, scalp, nails, and feet. Ringworm causes a reddish, circular rash that may itch or burn.
– Lice: These tiny wingless insects live on the skin and feed on blood. There are several different kinds of lice that can infest different parts of the body, including the head, body, and pubic area. Lice cause itching and may also be visible moving through hair.
– Botfly larvae: Botfly larvae infect humans when mosquitoes or other insects carry botfly eggs onto the skin. The larvae then burrow into the skin and develop, causing painful swelling, lesions, and skin irritation.
– Demodex mites: These microscopic mites naturally live in the hair follicles and oil glands of human skin. In large numbers, they can cause itching, redness, and other irritation. Demodex infestation is associated with skin conditions like rosacea.
Digestive Tract
Many parasites enter the body through contaminated food or water and settle in the digestive tract. Intestinal parasites can cause a diverse array of gastrointestinal symptoms, such as:
– Diarrhea
– Cramping and abdominal pain
– Nausea and vomiting
– Bloating or gas
– Weight loss
– Fatigue
– Change in appetite
Some intestinal parasites may also cause bloody stools or mucus in the stool. Common parasitic infections of the digestive tract include:
– Roundworms: Large, fat worms that live in the intestines. They rob nutrients and can cause symptoms like abdominal pain and diarrhea.
– Tapeworms: Long, flat worms that attach to the intestines. Tapeworms cause mild or even no symptoms in some cases. Main symptoms are diarrhea and abdominal discomfort.
– Giardia: Microscopic parasites that infect the small intestine. Giardia is spread through contaminated food and water and causes foul-smelling diarrhea.
– Cryptosporidium: Also spread through contaminated materials, Cryptosporidium causes watery diarrhea that can become life-threatening in those with weak immune systems.
– Amoebas: Microscopic parasites that are often spread through contaminated drinking water. They can invade different tissues and cause diarrhea, abdominal pain, and bloody stools.
Muscles and Joints
Some parasites have evolved clever ways of encysting themselves in human muscle or joint tissue. Symptoms may include:
– Muscle pain
– Joint swelling and stiffness
– Difficulty moving affected limbs
– Fatigue
– Fever
– Muscle or joint deformity in severe cases
Examples of parasites found in human muscle and joint tissue:
– Trichinella roundworms: These roundworms form cysts in muscle tissue, often from eating undercooked pork. Migration of larvae can cause muscle pain, fatigue, and swelling.
– Guinea worm: Guinea worm larvae infect people who drink contaminated water. The worms grow and mate in the abdomen before emerging through painful blisters on the skin.
– Toxoplasma gondii: This microscopic parasite forms cysts in muscle and brain tissue. It spreads through undercooked meat or contaminated water and causes flu-like symptoms.
Respiratory Tract
Airborne transmission allows some parasites to infect the lungs and respiratory system. Common respiratory symptoms may include:
– Cough
– Wheezing or difficulty breathing
– Chest tightness
– Fever
– Coughing up blood in severe cases
Parasites that can infect the respiratory tract:
– Ascariasis roundworms: Larvae migrate through the lungs before reaching the intestines. This can cause coughing, chest pain, and breathing issues.
– Paragonimus fluke worms: Spread through eating undercooked shellfish and crustaceans. These worms infect the lungs and cause fever, cough, chest pain and bloody sputum.
– Ascaris roundworms: Can cause a rare condition called Loeffler’s syndrome with symptoms like fever, cough, difficulty breathing and chest pain.
Eyes
Some parasites can infect the eyes or surrounding tissue, though this is relatively uncommon. Symptoms may include:
– Itching and irritation
– Swelling around the eyes
– Blurred or impaired vision
– Sensitivity to light
– Eye pain or redness
Examples of eye parasites:
– River blindness worms: Spread by flies, these worms infect the eyes and cause intense itching, eye lesions, and eventual blindness if untreated.
– Loa loa roundworms: Loa loa worms occasionally migrate through the whites of the eyes and can be seen moving. This causes red, itchy eyes.
– Toxoplasma gondii: While rare, eye infections can cause blurred vision, eye pain, and sensitivity to light.
Blood and Lymphatic System
Certain parasites invade the circulatory system and blood-forming organs like bone marrow. This can cause:
– Fever
– Chills
– Headaches
– Muscle and joint aches
– Enlarged liver or spleen
– Anemia
– Eosinophilia (increased eosinophils)
Examples include:
– Malaria: Caused by Plasmodium parasites and spread through mosquitoes. Invades red blood cells and causes cycles of severe chills and fever.
– Babesiosis: Babesia microbes infect red blood cells, causing flu-like symptoms, sweating, nausea, fatigue, and possibly dark urine.
– Leishmaniasis: Leishmania parasites infect certain white blood cells and cause skin lesions, fever, anemia, and enlarged spleen and liver.
– Schistosomiasis: Schistosoma worms penetrate the skin and migrate to the blood vessels around internal organs. They cause abdominal pain, fatigue, and blood in the stool or urine.
Brain and Nervous System
Infections of the brain and nervous system by parasites are quite rare but can be very serious. Neurological symptoms may include:
– Headaches
– Seizures
– Confusion
– Loss of coordination
– Numbness or weakness
– Behavioral changes
Examples of neurologic parasites:
– Naegleria fowleri: An amoeba that enters through the nose and infects the brain, causing severe headaches, nausea, and ultimately death.
– Toxoplasma gondii: While rare, this parasite can form cysts in the brain leading to headaches, seizures, and confusion.
– Neurocysticercosis: Taenia solium tapeworm larvae infect the central nervous system, causing seizures, headaches, or other neurologic issues.
How do parasites enter the body?
Parasites use a variety of methods to gain entry into the human body and establish an infection. Common routes of entry include:
Through the mouth
Many parasites are transmitted by the fecal-oral route – microscopic parasite eggs, larvae, or cysts enter the mouth from contaminated food, water, hands, or objects. Examples include roundworms, tapeworms, giardia, and cryptosporidium. Proper food handling and hygiene prevents these transmission routes.
Through the skin
Some parasites actively penetrate intact skin, while others enter through cuts or small abrasions. Hookworm larvae, schistosoma worms, and chiggers use this method. Wearing shoes and avoiding contaminated soil prevents skin penetration by some parasites.
Via insect vectors
Mosquitoes, ticks, flies, and fleas can carry parasitic diseases like malaria, African sleeping sickness, Chagas disease, and lyme disease. Avoiding habitats with these insect vectors limits transmission risk.
Through sex
Sexual contact spreads trichomoniasis and pubic lice. Practicing safe sex with barrier protection reduces transmission.
From mother to child
A few parasites like toxoplasma and malaria parasites cross the placenta and infect the fetus before birth. Screening and preventive medication during pregnancy protects the baby.
How do you know if you have parasites?
Identifying a parasitic infection can be challenging since symptoms are often nonspecific. Diagnosis requires considering risk factors and confirming parasites through laboratory tests.
Risk factors
People at higher risk may have:
– Traveled to or lived in a developing country
– Consumed contaminated food or water
– Close contact with animals
– Compromised immune system
– Exposure to unsanitary living conditions
Common symptoms
While shared symptoms like diarrhea or abdominal pain could indicate parasites, they often mimic other common conditions. Still, symptoms to look for include:
– Digestive complaints like diarrhea, nausea, gas, or cramps
– Coughing, wheezing, or fever if lungs are infected
– Itching skin, rashes, or lesions if skin parasites
– Muscle and joint pain
– Neurologic symptoms like headaches or seizures if the nervous system is affected
– General symptoms like fatigue, malnutrition, and unexplained weight loss
Diagnostic testing
To confirm parasites, doctors directly check stool, blood, tissue samples or other specimens for parasites or parasitic antibodies. Common diagnostics tests include:
– Microscopic examination for eggs, cysts, or larvae
– Stool antigen testing for certain parasites
– Blood smears to identify parasites in blood cells
– Biopsies or scrapings to visualize tissue-invading parasites
– Immunologic blood tests to detect parasitic antibodies
Treatment targets the specific parasite identified through diagnostics.
What are the most common parasites?
The distribution of parasitic diseases is not uniform around the globe – prevalence depends on sanitation levels, climate, and economic factors that promote transmission. However, some parasites are widespread. Common parasites worldwide include:
| Parasite | Location in Body | Transmission Route | Symptoms |
|---|---|---|---|
| Ascariasis roundworms | Intestines, lungs | Fecal-oral | Abdominal discomfort, coughing |
| Hookworms | Small intestine | Skin penetration | Abdominal pain, anemia |
| Trichuriasis whipworms | Large intestine | Fecal-oral | Diarrhea, abdominal pain |
| Giardia intestinalis | Small intestine | Fecal-oral | Diarrhea, bloating, nausea |
| Cryptosporidium | Intestines | Fecal-oral | Watery diarrhea |
| Toxoplasma gondii | Muscle, eyes, brain | Ingested oocysts from cat feces | Flu-like illness, blurred vision |
| Trichomonas vaginalis | Genitourinary tract | Sexual contact | Discharge, painful urination |
| Scabies mites | Skin | Skin contact | Rash, intense itching |
These examples represent just a fraction of known human parasites. The burden of parasitic disease depends greatly on living conditions, sanitation, and healthcare infrastructure in a given region.
Are parasites contagious?
Many parasites that infect humans are spread between people, making them contagious. However, contagion potential depends on the parasite species and transmission method.
Highly contagious parasites
Some parasites spread very easily through close contact, contaminated items, or poor hygiene:
– Pinworms: These intestinal worms spread quickly between children by contaminated fingers and surfaces.
– Scabies mites: Skin contact with an infected person easily transfers mites that burrow into the skin.
– Lice: Shared combs, clothing, and hats spread head and body lice, which need human blood to survive.
– Giardia: This diarrhea-causing parasite spreads rapidly through contaminated food and water sources.
Moderately contagious parasites
Certain parasites have specialized transmission methods that limit contagion between humans:
– Toxoplasma gondii: Mainly spreads through cat feces, not person-to-person contact.
– Malaria: Transmitted only by Anopheles mosquito vectors, not directly between people.
– Schistosomiasis: Requires specific freshwater snails to complete the parasite life cycle and infection route.
Non-contagious parasitic infections
Some parasites cannot spread between humans at all:
– Trichinella: Humans acquire infection by eating undercooked meat, not other humans.
– Cryptosporidium: Spreads through contaminated water, not person-to-person.
– Amoeba: Enters nose from contaminated freshwater sources.
The contagion threat underscores the importance of prompt diagnosis and treatment when parasites are suspected. This curtails spread to other people.
Can parasites be prevented?
While not always completely preventable, several key measures help reduce the risk of acquiring parasitic infections significantly.
Improved hygiene and sanitation
Many parasites capitalize on poor sanitation and hygiene habits. Strategies like:
– Access to clean drinking water and proper waste disposal
– Handwashing before eating and after using the bathroom
– Proper food handling and washing of produce
– Avoiding contamination of water or food by flies
Greatly reduce fecal-oral parasite transmission routes.
Vector and intermediate host control
Limiting contact with parasite vectors like mosquitoes, ticks, or freshwater snails controls transmission. Similarly, addressing parasite life cycle stages in animals prevents human infection. Examples include:
– Deworming pets and livestock
– Covering skin and using repellent to avoid insect bites
– Avoiding bodies of still, fresh water if schistosomiasis is common
– Not drinking untreated water
– Screening windows and doors to keep out flies and mosquitoes
Avoid transmission sources
Parasite life cycles and preferred host species mean certain sources are more likely to harbor infection. Avoiding these helps reduce exposure, such as:
– Not drinking untreated water
– Avoiding undercooked meat or fish
– Not swimming in pools, lakes, or rivers if you have open cuts or sores
– Using protection and avoiding questionable sexual partners
Healthy lifestyle
A strong immune system better controls parasite infections. Steps like eating nutritious food, exercising, and getting enough sleep improve overall health. Managing conditions like HIV or diabetes also keeps immunity strong.
Medications and vaccines
Certain anti-parasitic drugs or vaccines protect high-risk groups traveling to endemic areas. For example:
– Malaria prophylactic medication for travelers
– Immigrants and refugees may receive presumptive parasite treatment upon arrival
– Routine deworming of children in endemic regions
These medical interventions provide chemical barriers if parasites exposure still occurs.
Conclusion
Parasites have evolved complex life cycles and mechanisms enabling them to thrive in the human body. Symptoms caused by parasites depend on the species and location infected, ranging from mild discomfort to severe illness or death. Diagnosing and treating parasitic infections promptly reduces transmission and prevents complications. But the most effective long term strategy involves improving sanitation, eliminating vectors, creating barriers through medicine or vaccines, and empowering communities through education. An integrated approach addressing all routes of parasite transmission offers the best hope of reducing the substantial burden posed by these unique organisms.
