Toxocara canis and Toxocara cati are parasitic nematodes that reside in the small intestine of dogs, cats, and wild carnivores [24]. Human children are accidental hosts who become infected by ingesting infective eggs in contaminated soil. Following ingestion, the eggs hatch and larvae penetrate the intestinal wall and are carried by the circulation to the eyes, liver, heart, lungs, brain, or muscle. The larvae do not develop further in these sites, but the host inflammatory response against the migrating larvae can cause tissue damage [25]. They cause both visceral and ocular larva migrans in human. Heavy infection may result in fever, anorexia, malaise, irritability, hepatomegaly, respiratory symptoms, pruritic urticaria-like cutaneous lesions, and eosinophilia. Visceral larva migrans results in hepatitis and pneumonitis. Toxocariasis is a worldwide public health problem; however, infection tends to occur more frequently in tropical regions than in temperate regions [26].

Onchocerca volvulus is a filarial nematode transmitted by the Simulium blackfly resulting in onchocerciasis, a blinding disease. The blackfly and the disease are prevalent along the river in the endemic countries; hence, it is called “river blindness” [34]. It is endemic in Africa, Eastern Mediterranean, and Central and South America. Risk for travelers is generally low, unless travel involves extensive exposure to vectors in areas at risk. Humans are the main reservoir of onchocerciasis. The life cycle of Onchocerca volvulus begins when the female blackfly ingests microfilariae from infected human blood and the microfilaria develops into first-, second-, and third-stage larvae in the blackfly. When it bites another human, third-stage larvae get into the human and develop into adult worms. The adult worms settle in subcutaneous fibrous nodules, which are commonly known as onchocercomas. These firm painless nodules are predominantly seen on the head, face, and torso. Usually, the nodules are composed of 2–3 female worms and daughter microfilariae encapsulated in a fibrous coat. Microfilariae move across subcutaneous tissue and spread throughout the body, resulting in itching and dermal depigmentation. However, death of microfilariae causes an intense inflammatory reaction. The lymph nodes that drain the infected areas show granulomatous inflammation, fibrosis, and atrophy on histological examination.

Immunodiagnostic tests include enzyme-linked immunosorbent assay (ELISA) [40]. Rapid-format antibody card test is also available which requires a drop of blood from a finger prick. A positive test will result in a color change on the card surface. It is less expensive and it is as sensitive as ELISA. Card test does not require a lab setting and provides instantaneous results in the field [41]. Samples from skin snips or skin scratches can be used for polymerase chain reaction for detection of DNA [42].

Loaiasis is an infection by the filarial nematode Loa loa. The vectors are the flies from two species of the genus Chrysops, C. silacea, and C. dimidiate. Like onchocerciasis, the adult worms exist in the subcutaneous tissues in human beings and release sheathed microfilariae into the bloodstream in a diurnal rhythm. Microfilariae migrate rapidly in the body. The fly ingests microfilariae during a blood meal. After ingestion, the microfilariae develop into first-, second-, and third-stage larvae. The third-stage infective larvae can infect another human when the fly takes a blood meal [2].

Loa loa has a predilection for ocular tissues and is commonly known as the “eye worm.” Periocular subcutaneous macrofilariasis can present with intermittent attacks of painful lid swelling [47]. Often the worm can be seen in subconjunctival or subcutaneous plane as well. Blood films taken at noon and midnight are important in the detection and quantification of microfilaremia. Definitive diagnosis of filarial species can be made only after examination of the worm under the microscope. Improved molecular diagnostics for L. loa infection are needed not only in endemic areas but also in clinical laboratories of resource-rich countries to confirm infection in immigrants and travelers [48].

After topical anesthesia, a subconjunctival Loa loa worm can be removed with forceps through a conjunctival incision. Persons who undergo surgical removal of a worm may still have larvae in their blood, and they should be treated with diethylcarbamazine (DEC), 6 mg per kg body weight per day in three divided doses, administered orally for 3 weeks. This therapy kills both the larvae and the adult worms. DEC can cross the blood–brain barrier, and sudden death of many microfilariae can cause capillary blockage by dead and dying microfilariae in the brain, meninges, and retina, causing encephalopathy and death. In patients with more than 100 microfilariae per 50 cubic mm of afternoon blood, pretreatment with steroids should be considered before initiation of DEC therapy. Loa loa infection in endemic area complicates the mass treatment of onchocerciasis with ivermectin as its use in Loa loa patients might cause encephalitis. Albendazole therapy appears to be effective in killing adult worms and reduces the larval load. It is said to be useful in some loaiasis patients who have remained uncured after multiple courses of DEC treatment.

It is very important to understand that the patient’s history need not include recent travel to an endemic country. After inoculation by an infected fly, adult worms take approximately 3–4 years to mature in the human host. Consequently, Loa loa may present many years after the patient’s visit to an endemic region [49, 50].