Hookworms
| Characteristics | |
|---|---|
| Morphology | Hookworms are an intestinal parasite of humans. The larvae and adult worms live in the small intestine can cause intestinal disease. The two main species of hookworm infecting humans are Ancylostoma duodenale (A. duodenale) and Necator americanus (N. americanus). A. duodenale belongs to the family Ancylostomatidae and subfamily of Ancylostomatinae. N. americanus belongs to the family Ancylostomatidae and subfamily Bunostominae. Adults are slightly larger (male worms measure 8 to 11 by 0.4-0.5 mm, while the female is 10 to 13 mm long by 0.4-0.5 mm wide) than N. americanus (male worms measure 7 to 9 by 0.4-0.5 mm, while the female is 9 to 11 mm long by 0.4-0.5 mm wide). The buccal cavity which is in the opposite orientation to the curvature of body consists of cutting plates and gives the worm a characteristic hook appearance. Eggs (which are indistinguishable between the species) have a thin shell, are oval shaped, and are characterized by a clear space between the developing cells and the egg shell. |
| Growth Conditions | Agar plates containing nematode growth media (NGM) can be used to culture hookworm larvae. |
| Health Hazards | |
|---|---|
| Host Range | Humans, pigs, and hamsters |
| Modes of Transmission | Direct contact of soil containing larvae with unprotected skin. Infection can also be oral with direct maturation in the intestine to adult stage. Infection can be trans-placental or trans-mammary from mother to fetus/infant via infected placental/mammary tissue |
| Signs and Symptoms | Itching and a localized rash are often the first signs of infection. These symptoms occur when the larvae penetrate the skin. A person with a light infection may have no symptoms. A person with a heavy infection may experience abdominal pain, diarrhea, loss of appetite, weight loss, fatigue and anemia. The physical and cognitive growth of children can be affected. Mortality rate, worldwide, attributed to deaths occurring through direct hookworm infection, is estimated to be ~65,000 deaths annually. |
| Infectious Dose | Unknown; however, normal human volunteers infected with 10 N. americanus larvae, were positive by stools examination after 5 weeks post infection. |
| Incubation Period | Following penetration, the parasite migrates to the lungs within about 10 days. After 3 to 5 weeks, it passes through the gastrointestinal tract and attaches to the intestinal mucosa, where it matures into an adult worm and may stay for up to 1 year (5 years for N. americanus). Patent infections develop in 4-8 weeks following exposure. |
| Medical Precautions/Treatment | |
|---|---|
| Prophylaxis | Hygiene measures such as hand washing, drinking safe water, properly cleaning and cooking food, and wearing shoes. |
| Vaccines | None publically available |
| Treatment | Widely used antihelmintic agents are highly effective in treating infection. When anemia is mild or moderate, iron replacement is often adequate treatment. More severe anemia may require blood transfusions. |
| Surveillance | Monitor for symptoms. Stool analysis with quantitative egg counts include Kato-Katz test, concentration test, Beaver direct egg count, Stoll dilutional egg count, and McMaster techniques. PCR-based tests are the most sensitive that are utilized today. |
| GWU Requirements | Report all incidents to the Office of Risk Management as well as the Office of Research Safety (ORS) IMMEDIATELY FOLLOWING THE OCCURRENCE. |
| Containment | |
|---|---|
| BSL-2/ABSL-2 | Risk Group 2 classification is applied the parasite. BSL-2 and ABSL-2 practices, including appropriate PPE and containment equipment/facilities, are recommended for laboratory work with infective stages of the parasites discussed here (i.e., when there may be direct contact with samples with eggs, larvae, or from infected animal hosts). |
| Spill Procedures | |
|---|---|
| Small Spills (<1 liter) | If the spill occurred inside a biological safety cabinet, close the sash and allow the cabinet to operate for 15 minutes before continuing with the spill cleanup.
Hookworms are not known to be transmitted via aerosols, but caution should be taken during a spill outside of a BSC. Leave the room immediately and allow the aerosols to dissipate for 15 minutes. Notify others working in the lab. Don appropriate PPE. Cover area of the spill with paper towels or any absorbent material and apply an EPA registered disinfectant effective against the parasite (bleach, ethanol, iodine), working from the perimeter towards the center. Allow 30 minutes of contact time before disposal and cleanup of spill materials. |
| Large Spills | Alert lab personnel in the laboratory to the spill and keep people out of the area to prevent spread of the contamination. Check if you have been contaminated or if any of your PPE has been breached. If so follow exposure procedures. Remove any contaminated clothing and place it the biohazard waste. Wash your hands and post a sign on the door. Notify your supervisor of the incident and call ORS (4-8258) for assistance. If the situation involves an imminently life-threatening injury or has catastrophic potential, call 911. |
| Exposure Procedures | |
|---|---|
| Mucus Membrane | Flush eyes, mouth or nose for 15 minutes at eyewash station. |
| Other Exposure | For an area not protected by skin, wash with soap and water for 15 minutes (open wounds, sores, etc.). |
| Reporting | Report ALL injuries to the PI immediately and reported to the Office of Risk Management at [email protected] IMMEDIATELY FOLLOWING THE OCCURRENCE. Exposures that involve a bloodborne-pathogen or recombinant DNA also need to be reported to the Office of Research Safety at [email protected]. If the injury requires immediate medical attention, call GWPD at 202-994-6111 or call 911. |
| Medical Monitoring | Seek immediate medical evaluation, treatment, and post exposure follow-up at the Employee Health Office at GWU Hospital (900 23rd St., NW, Suite G-1090, Phone: 202-715-4275). Students should go to the Students Health Office at Marvin Center. After hours treatment can be received at the GWU hospital emergency room. |
| Stability | |
|---|---|
| Disinfection | Susceptible to 70% ethanol for 10 minutes, 0.5 % Dettol® for 20 minutes, chlorinated hydrocarbons (tetrachloroethylene). Sodium hypochlorite (1%) and glutaraldehyde (2%) are not effective. |
| Inactivation | Larvae are susceptible to high temperatures (>80oC), high salt concentrations, and freezing. N. americanus have lower survival times and physical resistance outside the human host compared to A. duodenale. Ancylostoma larvae cannot survive drying, or direct sunlight, and they cannot survive below 0 ºC or above 45 ºC. |
| Survival Outside Host | The infective larvae can survive for weeks under suitable conditions of moist, warm (temperatures around 30 °C), and shaded soil. |
| Personal Protective Equipment (PPE) | |
|---|---|
| Minimum PPE Requirements | At minimum, personnel are required to don gloves, closed toed shoes, lab coat, and appropriate face and eye protection prior to working with hookworms. Additional PPE may be required depending on lab specific SOPs. |
| Additional Precautions | Additional protection may be worn over laboratory clothing when infectious materials are directly handled, such as solid-front gowns with tight fitting wrists, gloves, and respiratory protection. Wash hands with soap and water after removing gloves. |
| References | |
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