Introduction

Definition of parasitic diseases

Parasitic diseases are illnesses caused by a parasite, which is an organisms that benefit from living in or on the host. They transmit diseases to the host through multiple ways, including a bite from an arthropod, such as a tick, as an intermediate vector (carrier).¹ Other ways include the host ingesting contaminated water or food. 

Importance of nutrition in overall health

A nutritional and balanced diet is vital for development and maintaining health. This is through the nutritional benefits to the immune system, boosting energy and mood. Furthermore, supporting an active lifestyle helps mental health and prevents the negative effects of being overweight.² 

Overview of the role of nutritional interventions in managing parasitic diseases

A parasite benefits from the source of nutritional value the host provides; this results in the host's nutritional status decreasing as the parasite infection causes the metabolic rate to increase.³ Additionally, the tissues have a pathological change as the appetite decreases and the immune response increases. The continued immune response causes the host to be malnourished from the additional drain from the parasite and under-eating. Ultimately, the patient develops greater susceptibility to further infections and the severity of the disease.⁴ 

Understanding parasitic diseases

Common types of parasitic diseases 

Common types of parasitic diseases include malaria, giardiasis, and helminth infections. Malaria is spread through mosquito bites, causing a high temperature, headaches, sweats, and chills, as well as stomach aches and diarrhoea.⁵ Another parasitic disease that can be caused by unsafe and unsanitary water is Giardia infections; this can cause stomach cramps, bloating, fatigue, watery, soft and greasy stools, with some experiencing weight loss and nausea.⁶ Parasitic worms are often found in contaminated soil, and their eggs can be transmitted via human faeces, which can cause helminth infection; this infection can result in impaired growth and development, with malnutrition and abdominal pain with diarrhoea.⁷ 

Health impacts 

Parasitic diseases often affect the nutritional status of the host and cause symptoms such as nausea and diarrhoea. These symptoms cause the loss of water, minerals and vitamins needed to maintain bodily functions.⁸ The dehydration and mineral deficiency, such as iron anaemia, impact the overall health of the patient. 

Current treatment options and limitations

The parasitic diseases can be treated with antiparasitics, antifungals, and antibiotics, with some infections requiring a combination of treatments. Antiparasitics, such as antiprotozoal agents, can be used to kill the parasite, stop the growth, or paralyse the parasite to treat the infection. Antifungal medicines treat the fungal parasites, such as ringworm, and can be referred to as antimycotics.⁹ For example, azoles inhibit the growth of the fungi. Antibiotics are used to kill bacteria or prevent them from multiplying. These treatment options for parasites have limited effectiveness due to a vast genetic variation in parasites and growing drug resistance.¹⁰ Drug resistance allows stronger variants of the parasites to reproduce and makes it challenging to find effective treatment options. The parasitic medication options can cause side effects and adverse reactions in some individuals; side effects include abdominal pain, diarrhoea, anaphylaxis, jaundice, fever, headache, itchy skin, and vomiting.

The role of nutrition in immune function

How malnutrition weakens the immune response 

The first line of defence is the innate immune system through protective barriers, such as the skin, mucus, stomach acid, and immune cells. The adaptive immune system is the body's specific white blood cells that adapt to the foreign substance to quickly and efficiently destroy the pathogen ¹². However, when the body is in a state of malnutrition, the immune cells that support the immune system cannot develop. Furthermore, malnutrition causes decreases in immune cell metabolism and population, as well as hormones. Therefore,  the immune system becomes compromised, and mucosal damage makes the patient more susceptible to disease.¹³ As the micronutrients needed for the amino acids, oligosaccharides and short-chain fatty acids for the inflammatory functions. 

The impact of a strong immune system on parasitic infection outcomes

A strong immune system has many lines of defence in the body. These prevent parasitic infection with physical barriers, such as saliva and mucus. If these fail, a strong immune system has a specific and non-specific antibody defence system.¹⁴ A non-specific immune response consists of multiple immune cells, such as neutrophils, eosinophils, and basophils, whereas a specific immune response involves lymphocytes that have specific antibodies for the invading pathogen. After recovery, white blood cells with the antibodies for that pathogen remain, which allows for future infections from the same pathogen to have a minimal impact on the individual.¹⁵ 

Nutritional interventions in parasitic disease management

The incorporation of anti-inflammatory foods can aid the immune system and have some antiparasitic effects. Some examples of this include garlic, onions, herbs, coconut oil, pineapple, and apple cider vinegar. Overall, foods with antibacterial effects that regulate and restore healthy pH and improve digestion, support the daily bodily functions to fight off infection.¹⁶ However, foods to avoid include alcohol, which reduces the immune system's function. Other foods, such as pork, can be a source of parasites, and dietary sugars can feed the parasites. Furthermore, added sugars, wheat containing gluten, and processed foods can increase inflammation and are harder to digest, which could cause the infection to worsen.¹⁷ 

Probiotic foods, such as yoghurts, kefir, and fermented foods, can improve your gut health. Furthermore, increasing dietary fibre and hydration stimulates the immune system.¹⁸ Additionally, supplementation of seeds, such as papaya and pumpkin, can reduce parasitic numbers. Moreover, strengthening the immune system via selenium, zinc, and vitamin A supplements can be beneficial. 

Case studies and evidence

Evidence suggests young children with acute malnutrition are at risk of having slower parasite clearance, reinfections, and treatment issues. Moreover, the medical intervention was less effective as malnutrition reduced the absorption and metabolism in children.¹⁹ Further connections between diet, parasite resistance and the gut microbiome influence the antimicrobial properties in the immune system and the peptide recognition receptors against the parasites; this highlights the importance of diet because it strengthens the gut microbiome to increase disease resistance. Furthermore, the host and gut microbiome symbiosis aids in suppressing infectious diseases.²⁰ 

Limitations and challenges 

Parasitic zoonoses have a variety of symptoms in humans, which can make it challenging to standardise and differentiate symptoms and treatments; this challenge is developing with further emerging parasites and resistance increasing.²¹ The development of treatment options for parasitic infections is lower than other novel treatment options, such as vaccines and chemotherapy, thus slowing the progression of these diseases. Alternatively, the One Health approach addresses the complex interconnections between the health of humans, animals and ecosystems. Therefore, One Health requires a multidisciplinary approach to reduce the spread of parasitic infections.²²

Cultural and religious beliefs, such as not eating pork in Judaism and Islam, reduce the individual risk of parasite exposure. However, cultural diets including raw fish and vegetables, for example, sushi, increase exposure. The reduction of these foods in their diet could be culturally insensitive.²³  Furthermore, social living costs and limited access to food increase the transmission of parasitic infections. 

Conclusion

Nutrition plays an important role in supporting the immune system against parasitic infections and reducing the risk of disease transmission. The optimisation of an individual's diet can support the immune system's defence against infection; this can be achieved by contacting nutritionists and following diet plans for the incorporation of beneficial foods and vitamins. Furthermore, research and public health initiatives focused on nutrition and parasitic disease management are required for successful treatment plans and options.