What Is Parasitology? A Guide to the Field

Parasitology is the scientific study of parasites — organisms that live on or in a host and draw their nourishment from it — together with their hosts and the relationships between the two. It is a discipline defined by a way of living rather than by a single taxonomic group, which is why it draws on zoology, microbiology, immunology, ecology, epidemiology and, increasingly, genomics. This guide explains what parasitology covers, its main subfields (protozoology, helminthology and the study of arthropod vectors), the methods the field relies on, why it matters for global health, which professional societies and journals anchor it, how it is funded, and how people train for it.

What Is Parasitology?

A parasite is an organism that depends on another living organism, its host, for food and habitat, usually at some cost to the host. Parasitology studies the biology of those organisms — their life cycles, structure, metabolism, genetics and evolution — and the other side of the interaction: how hosts detect, resist, tolerate or succumb to infection. It also covers the ecology of transmission (how a parasite moves from one host to the next, often through a vector or an intermediate host) and the practical problems that follow: diagnosis, treatment, prevention and control.

Three features make the field distinctive. First, the organisms are taxonomically diverse: single-celled protozoa, multicellular worms (helminths) and arthropods such as ticks, mites and lice are all studied under one roof. Second, many parasites have complex life cycles with several developmental stages, sometimes in several different host species, so understanding one parasite means understanding more than one animal. Third, the field is unusually applied. Some of the world’s most consequential infectious diseases, malaria among them, are parasitic, so basic parasitology feeds directly into medicine, veterinary science and public health.

Parasitology is usually treated as a branch of the life sciences with close ties to microbiology, immunology and biology generally. Where it differs from microbiology in the narrow sense is that most medically important parasites are eukaryotes, with cell biology far closer to their human or animal hosts than bacteria or viruses are, which is part of why antiparasitic drug discovery is hard.

The Main Subfields of Parasitology

Protozoology

Protozoology is the study of parasitic protozoa: single-celled eukaryotes that infect humans and animals. Well-known examples include Plasmodium (the genus that causes malaria), Trypanosoma (African sleeping sickness and Chagas disease), Leishmania (the leishmaniases), Toxoplasma gondii, Giardia and Cryptosporidium. Research questions range from how a parasite invades and remodels a host cell, to how it varies its surface proteins to evade the immune system, to why some populations evolve resistance to a drug.

Helminthology

Helminthology is the study of parasitic worms. The major groups are the nematodes (roundworms, including hookworms and the filarial worms), the trematodes (flukes, including the schistosomes) and the cestodes (tapeworms). Helminths are generally large enough to see without a microscope at some stage, and many cause chronic, long-lasting infections rather than acute illness. Helminthologists study worm development and reproduction, the immune responses that worms provoke — often distinctly different from responses to microbes — and the interaction between worm infection and other conditions.

Medical and Veterinary Parasitology

Medical parasitology focuses on parasites that infect people: clinical presentation, laboratory diagnosis, treatment and public health control. Veterinary parasitology does the same for livestock, companion animals and wildlife, and the two overlap wherever a parasite moves between animals and people (zoonotic infections). Because the same parasite or vector can matter to a clinic, a farm and a wildlife reserve, the field has a strong tradition of treating human and animal health together; see our guide to veterinary science for the animal-health side of that relationship.

Vector Biology and Medical Entomology

Many parasites are carried between hosts by arthropod vectors: mosquitoes transmit malaria and filariasis, tsetse flies transmit African trypanosomes, sandflies transmit Leishmania, and triatomine bugs transmit the parasite that causes Chagas disease. Vector biology studies these carriers — their ecology, behavior, feeding, genetics and susceptibility to the parasite — because breaking transmission at the vector is often the most effective way to control disease. NIAID, for example, runs a Vector Biology Research Program supporting work on vectors of neglected tropical diseases. This is the point where parasitology meets entomology; an entomologist who studies mosquitoes and a parasitologist who studies the malaria parasite are often working on two halves of the same transmission cycle.

Related Specialties

Beyond these core areas, parasitologists work in molecular and genomic parasitology (sequencing parasite genomes, tracking drug-resistance markers), parasite immunology and vaccinology, ecological and evolutionary parasitology (including host-parasite coevolution), and parasite epidemiology, which applies the tools described in our epidemiology guide to questions of prevalence, risk and intervention impact.

A Brief History

People described parasitic worms long before they understood what they were, but modern parasitology took shape in the nineteenth century. In 1880 the French military physician Alphonse Laveran identified malaria parasites in human blood. In 1897 Ronald Ross demonstrated that mosquitoes carry the malaria parasite, a finding that established the central idea of vector-borne transmission and later earned him a Nobel Prize in Physiology or Medicine (1902), with Laveran receiving the same prize in 1907. In the twentieth century the field professionalized: dedicated societies and journals appeared, and antiparasitic chemotherapy matured. That legacy was recognized again in 2015, when the Nobel Prize in Physiology or Medicine went to William Campbell and Satoshi Omura for avermectin, the basis of ivermectin, and to Tu Youyou for artemisinin, the foundation of modern malaria treatment.

The American Society of Parasitologists was formed on December 30, 1924, in Washington, DC, by William Walter Cort and Henry Baldwin Ward, with Ward as its first president. The American Society of Tropical Medicine and Hygiene traces its origin to the Society of Tropical Medicine of Philadelphia, founded in March 1903 by a group of 28 physicians and renamed the American Society of Tropical Medicine days later; the present society was formed in 1951 through a merger with the National Malaria Society.

Methods and Tools in Parasitology

• Microscopy and morphology. Identifying parasites in blood films, stool samples and tissue by their appearance remains a foundation of both teaching and clinical diagnosis. The CDC maintains a public diagnostic resource, DPDx, for laboratory identification of parasites.
• Culture and animal models. Some parasites can be grown in vitro (certain malaria and trypanosome stages, for example), while others require laboratory animals or insect colonies to complete their life cycle. Work with animals falls under institutional oversight such as an animal care and use committee, and work with infectious agents under institutional biosafety review; see our entries on BSL-2 and the IACUC versus IBC distinction.
• Molecular diagnostics and genomics. PCR-based detection, whole-genome sequencing and population genetics are used to identify species, follow transmission and monitor genetic markers of drug resistance.
• Immunological assays. Antibody and antigen tests support diagnosis and serological surveys of exposure in a community.
• Field and epidemiological methods. Community surveys, vector sampling, mass drug administration trials and surveillance link laboratory findings to disease burden. Field studies in endemic regions raise their own ethics and governance questions, including partnership with local institutions and research in low- and middle-income countries.
• Drug and vaccine development. Screening compounds against parasites, testing candidate vaccines and running clinical trials, including under Good Clinical Laboratory Practice (see GCLP).

Why Parasitology Matters for Global Health

Parasitic disease is concentrated in tropical and subtropical regions and falls hardest on the poorest communities. Malaria is the clearest example. The World Health Organization estimates 282 million malaria cases and 610,000 deaths across 80 countries in 2024, with the WHO African Region accounting for about 95% of cases and deaths and children under five making up roughly three quarters of deaths in Africa. WHO now recommends two malaria vaccines, RTS,S/AS01 and R21/Matrix-M, alongside insecticide-treated nets and artemisinin-based combination therapies. Several other parasitic infections, such as leishmaniasis and Chagas disease, are classed among the neglected tropical diseases, which attract far less commercial investment than their burden would suggest and therefore depend heavily on public and philanthropic research funding.

Research on these diseases is global by nature, and it raises standard research-administration questions: international subawards, data sharing, benefit-sharing with host-country partners and the use of the LMIC label in funding rules. Funders working in this area include philanthropies such as the Gates Foundation; see our overview of Gates Foundation research grant programs.

Professional Societies and Journals

Two U.S. societies anchor the field and are the usual starting points for meetings, networking and awards:

• American Society of Parasitologists (ASP). Founded in 1924, ASP is a society for professional parasitologists. Its official publication is the Journal of Parasitology, which Henry Baldwin Ward founded in 1914 and which the society adopted as its official journal in 1931. It is published bimonthly.
• American Society of Tropical Medicine and Hygiene (ASTMH). ASTMH brings together clinicians, researchers and public health practitioners working on tropical disease. Its official scientific journal is the American Journal of Tropical Medicine and Hygiene.

Other widely read journals in the field include Parasitology, Trends in Parasitology, the International Journal for Parasitology, Malaria Journal and PLOS Neglected Tropical Diseases. Researchers choosing where to publish should compare scope, open access terms and indexing for their own subfield.

How Parasitology Research Is Funded

In the United States the largest public funder of parasitology relevant to human disease is the National Institutes of Health, principally through the National Institute of Allergy and Infectious Diseases (NIAID). NIAID states that it has a long-standing program to understand, treat and prevent neglected tropical diseases, conducting its own studies and supporting researchers in the United States and in countries where these diseases are widespread. Its priorities include malaria and other parasitic diseases, and its funding history includes Tropical Medicine Research Centers set up in 2012 to build research capacity in endemic areas. For a view of how NIAID turns review scores into funding decisions, see our entry on the NIAID payline.

Applicants should check current funding opportunities directly with NIH and NIAID, because program priorities and announcement numbers change. Outside NIH, parasitology is also supported by other U.S. agencies, international bodies, national research councils and private philanthropy, with the mix depending on whether the work is human, veterinary or agricultural. Whatever the source, an award brings the usual compliance obligations: animal-use approval, biosafety review, data management and sharing plans, and, for field work abroad, local ethics approval and subaward management. Grant-seekers new to this area may want the wider research methods hub for context on study design and measurement.

Training and Career Paths

There is no single route into parasitology. Common paths include:

• Undergraduate preparation in biology, zoology, microbiology or a related life science, ideally with laboratory and field experience.
• Graduate study (MS or PhD) in a parasitology, microbiology, immunology, tropical medicine, ecology or public health program, often with a lab that focuses on a single organism or vector.
• Medical and veterinary training, followed by fellowships in infectious diseases or tropical medicine for those who want a clinical career.
• Postdoctoral research, frequently funded by an individual fellowship or by a principal investigator’s grant.

Careers span university and institute research, government agencies and public health laboratories, global health organizations, the pharmaceutical and diagnostics industries, veterinary and agricultural services, and teaching. Fieldwork and collaboration with partners in endemic countries are common, so language skills, comfort with international research administration and a willingness to travel are practical assets.

How Parasitology Connects to Research Administration

For research administrators, parasitology projects tend to combine several compliance streams at once. Infectious agents trigger biosafety review. Animal models and vector colonies trigger animal care oversight. Specimens and isolates moved across borders may require permits and material transfer agreements. International fieldwork brings foreign subawards, local ethics approval and export or import rules. Understanding that a single project may touch all of these helps offices plan timelines and budgets realistically, and it is why parasitology grants often benefit from early coordination between investigators and their research offices.

Frequently Asked Questions

What is the difference between parasitology and microbiology?

Microbiology studies microorganisms in general, mainly bacteria, viruses, fungi and protozoa. Parasitology is defined by the parasitic way of life and so includes multicellular parasites such as worms and arthropods that microbiology does not usually cover, while only some microbes are parasites. In practice the fields overlap heavily, especially in protozoology.

What does a parasitologist do?

Parasitologists study how parasites live, spread and cause disease and how hosts respond. Depending on the setting, that may mean laboratory research on a single organism, field surveys in endemic regions, clinical or veterinary diagnosis, vector control, or drug and vaccine development.

What is the difference between parasitology and tropical medicine?

Tropical medicine is a clinical and public health specialty concerned with diseases common in tropical regions, which include bacterial and viral as well as parasitic infections. Parasitology is a biological discipline organized around parasites wherever they occur. The two overlap heavily, which is why societies such as ASTMH include both.

What are the main types of parasites?

The three major groups studied are protozoa (single-celled organisms such as Plasmodium), helminths (parasitic worms: nematodes, trematodes and cestodes) and ectoparasitic arthropods such as ticks, mites and lice.

Which societies and journals should I know?

The American Society of Parasitologists and its Journal of Parasitology, and the American Society of Tropical Medicine and Hygiene and its American Journal of Tropical Medicine and Hygiene, are the main U.S. anchors.

Who funds parasitology research?

In the United States, NIH, mainly through NIAID, is the principal public funder for human-disease-related work, supplemented by other agencies, international bodies and philanthropies such as the Gates Foundation.

This page is general educational information about a scientific discipline. It is not medical advice; anyone concerned about a possible parasitic infection should consult a qualified clinician. Statistics are drawn from the World Health Organization, NIAID and society websites as of October 2026 and should be checked against current sources before citation.