| Necatoriasis | |
|---|---|
 | |
| Infective larva ofNecator americanus | |
| Specialty | Infectious diseases  |
Necatoriasis is the condition of infection byNecatorhookworms, such asNecator americanus.[1] Thishookworm infection is a type ofhelminthiasis (infection) which is a type ofneglected tropical disease.
When adult worms attach to thevilli of thesmall intestine, they suck on the host's blood, which may cause abdominal pain, diarrhea, cramps, and weight loss that can lead to anorexia. Heavy infections can lead to the development ofiron deficiency andhypochromic microcytic anemia. This form of anemia in children can give rise to physical and mental retardation. Infection caused by cutaneous larvae migrans, a skin disease in humans, is characterized by skin ruptures and severe itching.[2]
Necatoriasis is caused byN. americanus.N. americanus can be divided into two areas – larvae and adult stage. The third stage larvae are guided to human skin by following thermal gradients.[3] Typically, the larvae enter through the hands and feet following contact with contaminated soil. A papular, pruritic, itchy rash will develop around the site of entry into the human host.[4] This is also known as "ground itch". Generally, migration through the lungs is asymptomatic but a mild cough and pharyngeal irritation may occur during larval migration in the airways. Once larvae break through thealveoli and are swallowed, they enter the gastrointestinal tract and attach to theintestinal mucosa where they mature into adult worms. The hookworms attach to the mucosal lining using their cutting plates which allows them to penetrate blood vessels and feed on the host's blood supply. Each worm consumes 30 μl of blood per day. The major issue results from this intestinal blood loss which can lead to iron-deficiency anemia in moderate to heavy infections. Other common symptoms includeepigastric pain and tenderness, nausea, exertionaldyspnea, pain in lower extremities and in joints, sternal pain, headache, fatigue, and impotence.[5] Death is rare in humans.[citation needed]
The standard method for diagnosing necatoriasis is through identification ofN. americanus eggs in a fecal sample using a microscope. Eggs can be difficult to visualize in a lightly infected sample so a concentration method is generally used such asflotation or sedimentation.[6] However, the eggs ofA. duodenale andN. americanus cannot be distinguished; thus, the larvae must be examined to identify these hookworms. Larvae cannot be found in stool specimens unless the specimen was left at ambient temperature for a day or more.[citation needed]
The most common technique used to diagnose ahookworm infection is to take a stool sample, fix it in 10%formalin, concentrate it using the formalin-ethyl acetate sedimentation technique, and then create awet mount of the sediment for viewing under a microscope.[citation needed]
Education, improvedsanitation, and controlled disposal ofhuman feces are critical for prevention. Nonetheless, wearing shoes inendemic areas helps reduce the prevalence of infection.[citation needed]
An infection ofN. americanus parasites can be treated by usingbenzimidazoles:albendazole ormebendazole. A blood transfusion may be necessary in severe cases of anemia. Light infections are usually left untreated in areas where reinfection is common. Iron supplements and a diet high in protein will speed the recovery process.[7] In a case study involving 56-60 men withTrichuris trichiura and/orN. americanus infections, both albendazole and mebendazole were 90% effective in curingT. trichiura. However, albendazole had a 95% cure rate forN. americanus, while mebendazole only had a 21% cure rate. This suggests albendazole is most effective for treating bothT. trichiura andN. americanus.[8]
Cryotherapy by application of liquid nitrogen to the skin has been used to kill cutaneous larvae migrans, but the procedure has a low cure rate and a high incidence of pain and severe skin damage, so it now is passed over in favor of suitable pharmaceuticals. Topical application of some pharmaceuticals has merit, but requires repeated, persistent applications and is less effective than some systemic treatments.[9]
During the 1910s, common treatments for hookworm includedthymol,2-naphthol,chloroform,gasoline, andeucalyptus oil.[10] By the 1940s, the treatment of choice wastetrachloroethylene,[11] given as 3 to 4 cc in the fasting state, followed by 30 to 45 g ofsodium sulfate. Tetrachloroethylene was reported to have a cure rate of 80 percent for Necator infections, but 25 percent in Ancylostoma infections, and often produced mild intoxication in the patient.
Necator americanus was first discovered in Brazil and then was found in Texas. Later, it was found to be indigenous in Africa, China, southwest Pacific islands, India, and Southeast Asia. This parasite is a tropical parasite and is the most common species in humans. Roughly 95% of hookworms found in the southern region of the United States areN. americanus. This parasite is found in humans, but can also be found in pigs and dogs.[citation needed] Infections withNecator americanus have been historically reported in the Southern United States; in 1905 more than 40% of Southerners were infected[12]; in the 1930’s a national survey reported 53-75% prevalence in some areas[13]; 19.6% infection rates in Southern US and Appalachia in 1982 were documented[12]. Research into this disease burden includes surveys and questionnaires, stool sample collection, and detection of parasite DNA[13][14]. In 2017 infections were associated with poverty, with high prevalence reported in black residents of Lowndes County, Alabama[12]. Social determinants of health contribute to this ongoing health inequity[15]. In 2020, 69.8% of the population of Lowndes County, Alabama was labeled as black or African American[16] compared to the national average in the same year of 12.1%[17]
Transmission ofN. americanus infection requires the deposition of egg-containing feces on shady, well-drained soil and is favored by warm, humid (tropical) conditions. Therefore, infections worldwide are usually reported in places where direct contact with contaminated soil occurs.[citation needed]