Summary
Highlights
Arthropods are ectoparasites that live on the surface of the body, often feeding on blood or skin. They are characterized by an exoskeleton and articulated legs. While many species exist, only a few are harmful to humans. They can cause illness either through allergic reactions to their presence or by acting as vectors for infections.
The first way arthropods make you sick is an allergic response to their antigens, such as saliva injected during a blood meal. This leads to an inflammatory response, causing itchy, red, raised papules. Examples include bites from mosquitoes, fleas (like Pulex irritans, causing a linear 'breakfast, lunch, and dinner' bite pattern), ticks, mites, and lice. Mites, such as Sarcoptes scabiei (scabies), burrow into the skin, laying eggs and defecating, causing irritation. Severe cases, like Norwegian scabies, can occur in immunocompromised individuals.
The second way arthropods cause illness is by acting as biological vectors, transmitting bacteria, viruses, and other parasites. Ticks (eight-legged) prefer animals but can accidentally bite humans. Hard ticks (e.g., Ixodes scapularis) spread Lyme disease, while both hard and soft ticks can transmit other infections like Rickettsia, Anaplasma, and Babesia.
Lice (six-legged) prefer humans. Pediculus capitis (head louse) spreads by direct head-to-head contact. Pediculus humanus (body louse) lives in clothing seams and can spread epidemic typhus (Rickettsia prowazekii), trench fever, and louse-borne relapsing fever. Pthirus pubis (pubic/crab louse) infests pubic hair and can be sexually transmitted.
Mites (eight-legged) are tiny and can spread diseases like Rickettsial pox and scrub typhus, though scabies itself isn't a vector. Fleas (six-legged) are epic jumpers; rat fleas (Xenopsylla cheopis) are known to spread bubonic plague, tularemia, and murine endemic typhus. Mosquitoes (six-legged) are major vectors: Culex spreads filariasis and West Nile; Aedes aegypti and Aedes albopictus spread yellow fever, dengue, and chikungunya; Anopheles is the vector for malaria.
Diagnosis often involves visually identifying the bug, such as a tick. For scabies, skin scraping can reveal eggs or adult mites under a microscope. Sometimes, only the eggs (nits from head lice) or the characteristic bite patterns (e.g., linear bites) are visible. In other cases, the diagnosis of a specific infection (like epidemic typhus) implies an arthropod infestation, necessitating decontamination.
Treatment includes symptomatic relief for bites (anti-inflammatories, antihistamines) and addressing secondary skin infections. If a vector-borne infection is suspected, it must be treated. For active infestations, removal methods include careful tick removal with tweezers. Topical or systemic treatments (e.g., ivermectin) are used for lice and mites. Prevention focuses on improving sanitation, housing, and clothing.
Arthropods are tiny animals with exoskeletons, found globally. Many are anthropophilic, while some prefer other mammals. Infestations cause allergic dermatitis and can transmit infections. Diagnosis involves identifying bites, burrows, adults, or eggs, or inferring from the illness. Treatment includes removal, topical/oral agents, and symptomatic care. Prevention relies on sanitation, better housing, and clothing.