Self-treating with NA

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    Necator americanus (NA) is a member of the phylum Nematoda and primarily found naturally in tropical and temperate regions. Commonly known as the New World hookworm, it is one of only three hookworms that are adapted to living in humans, and the only one used in helminthic therapy. (The other two hookworms are the Old World hookworm, Ancylostoma duodenale, which is abundant throughout the world, and Ancylostoma ceylanicum which is also adapted to cats and found predominantly in Southeast Asia and the Pacific. [1] [2])

    Dosing with hookworms

    See the following page.

    Hookworm larvae storage and survival

    Ideally, L3 NA larvae should be used as soon as possible after cultivation because, at this stage in their development, the larvae do not feed and therefore rely on their fat stores for nourishment, and they become increasingly weaker as these stores are used up.

    Home-grown larvae have been known to survive for as long as 3-5 months if kept in ideal conditions, i.e., out of light, at a temperature of 60-65°F (15-18°C), in a minimal amount of distilled, demineralised or dechlorinated water. [3] [4] (Researchers working with NA larvae have reported that the pressure from too large a volume of water will shorten their life.) Survival time is also partly determined by the temperature at which the larvae were incubated, with those grown at a lower temperature having greater longevity.

    Larvae purchased from the helminth providers may not last as long as home-grown larvae because the providers put them through a cleaning process which reduces their longevity. Variations between the cleaning protocols used by different providers result in differing lengths of shelf life. For example, one hookworm provider (Wormswell [2014-2018]) said that their larvae had a shelf life of 3 to 4 weeks after rinsing, whereas larvae purchased from a different provider (Worm Therapy) only have a stated shelf life of 2 weeks.

    Purchased hookworm larvae should therefore be used as soon as possible after receipt. If there is an unavoidable delay in inoculating with the larvae, the provider should be consulted, and, in the meantime, the larvae should be stored in their original packaging at room temperature and out of direct sunlight.

    Worm growers have reported a 50% loss of larvae at 50ºF (10ºC) and a 90% loss if the temperature drops to 43ºF (6ºC) for several hours. Hookworm larvae are also susceptible to drying and heat, for example from direct sunlight. [5] (PDF) Temperatures above 113ºF (45ºC) will kill them, and they may only last for a week or two at 90ºF (32ºC). Personal experiences include the following.

    I find the larvae don't really like it too warm. I just keep them at room temperature, which ranges from 16-20 degrees Celsius. They last a good month but there is some attrition. Say 10-20 percent. [6]
    I keep mine in the wardrobe of the coldest room of the house which can be between 12-20 °C. I also close the little lid on of the micro tube so the tube is sealed. [7]

    If L3 larvae encounter extreme temperatures during transit, they may be dead on arrival. (See Losses during shipping.) Sitting in an outdoor mailbox in sub-zero temperatures will also be fatal for the larvae, so delivery should be arranged to an address where the package can be received indoors.

    Hookworm inoculation

    NA larvae are applied to the skin on a bandage/dressing and should be used as soon as they are available.

    They can survive for as long as 3-5 months if kept at a favourable temperature (70ºF/21ºC), although their longevity is also dependent on the temperature at which they were incubated, with larvae grown at a lower temperature surviving for longer. Since they do not feed at this stage in their development, the larvae are reliant on their fat stores, which obviously diminish over time, rendering them progressively weaker. For more detail, see Hookworm larvae storage and survival, above.

    After being pipetted onto a bandage/dressing, the hookworm larvae should be applied to a hairless, convex area of skin to ensure good skin contact, as demonstrated in the following instructional video.

    There can be stragglers trapped in water droplets in the vial after the contents have been pipetted onto a bandage/dressing, so at least one rinse should be carried out, and some providers supply a vial of distilled water for this purpose. Even a second rinse can sometimes capture the odd straggler. [8]

    If inoculating with home-grown larvae, use a bandage/dressing with a flat central pad in preference to the quilted type. A Band-Aid dressing with a ⚠️"Quilt-Aid Comfort Pad" has been reported to have prevented successful inoculation in one case. [9]

    If a ready-made bandage/dressing is not available, an effective substitute can be made by using a makeup pad, or by cutting the required size from a large lint pad and securing this to the skin with medical tape. [10]. Alternatively, a piece of toilet paper, or flat paper towel, stuck to a piece of masking/painter's tape will work. [11] [12]

    Some self-treaters have found that placing the larvae on multiple bandages/dressings greatly reduces the itch and rash that often develop following inoculation using a single bandage/dressing.

    I normally inoculate with about 10 NA's on one patch, but that gave me much itching and bumps. Then I did 10 with just one larva on each patch: no itching, no bumps AND not always visible entry points. [13]

    Alternatively, the larvae can be spreaad more widely on a larger bandage/dressing to help reduce the intensity of the inoculation rash and itch.

    Now I use big bandages and try to dot the water all over, instead of squirtng it in one spot. [14]

    Some hookworm suppliers have experimented with pre-loading the larvae onto a small damp cotton patch, which the user then placed onto a larger bandage/dressing after receipt, before applying this to their skin. This method was eventually abandoned after if proved to be less successful than the traditional method requiring the self-treater to pipette the larvae from an eppendorf tube onto a bandage/dressing.

    After the bandage/dressing has been applied, the larvae will detect the presence of skin [15] [16] and, responding in particular to warmth, [17] will swing into action, often producing an itch within just a few minutes. Occasionally, the itch may be delayed for up to several hours, [18] or even until the next day. [19]

    The bandage/dressing should be left in place for a minimum of four hours and, ideally, for twelve hours. If you need to take a shower before the bandage/dressing is due to come off, cut a piece from a plastic bag and tape this over the area to keep it dry. [20] Duct tape or electrical insulation tape are ideal for this purpose because they are waterproof.

    When the bandage is removed, this may reveal the beginnings of a rash. For more about this and how to treat the itch, see the following page.

    Best time of day to inoculate with NA

    Different self-treaters prefer to inoculate at different times during the day.

    I get a very aggressive itch, so I always inoculate in the morning. This way, I can distract myself during the day. I take the bandage/dressing off before I retire for the night, and take my hair dryer to bed with me. [21]
    I like to inoculate at night because I sleep through the itch! I hair dryer in the morning. [22]

    Body sites used for hookworm inoculation

    The inside of the forearm or bicep is a good choice because it is convenient to access in order to treat the rash with creams or apply hot air from a hair dryer, but inoculation too close to the armpit can cause lymph nodes there to swell. Inoculation high on the inner thigh - and even occasionally on the outer thigh [23] - can cause painfully raised lymph nodes in the groin, which can be uncomfortable when walking. [24]

    Many hookworm hosts have found that repeatedly using the same site results in a more robust skin reaction, and that varying the site effectively reduces both the rash and the itching.

    NB. The feet are best avoided by diabetics and first time inoculators.
    • Wounds on the feet tend to heal more slowly in patients with diabetes. Even a small foot wound can quickly develop into a ulcer in diabetics, and they are 15 times more likely to need amputations as a result of foot wounds or ulcers.
    • The underside of the foot may not be a good place for the first inoculation because the skin response is often reduced at this site, increasing the possibility of getting no noticeable skin response at all, which may lead a new hookworm host to assume that the dose was dead, when it might not have been. This may result in them ordering a replacement dose, and risking more severe side effects from what would then have become a double dose. The arm is therefore arguably a better choice for the first dose, and the foot can be used once the individual has more experience with the inoculation process. [25]

    All the sites mentioned below have been used.

    Treated on the bottom of my foot 2 days ago. So far there’s barely any response, it’s definitely an improvement compared to other areas of my skin. [26]
    My husband's NA rash on his forearm became intolerable... his whole arm would swell and the whole tissue would itch insanely. He really was reluctant to inoculate any more larvae. After ten months his snoring returned, so I convinced him to try the sole of his foot... he chose the instep. I thought I would try my heel. We both experienced a very slight tingle for a second about an hour after inoculation. The next morning my husband had clear signs of larvae entry and a very mild irritation... me, nothing. After 3 days my husband's foot is just fine... the rash does not bother him at all... and my heel has only just started to indicate that larvae entered the skin... with an almost unnoticeable itch... like I have a tiny prickle in my foot. [27] I have tried both my heel and instep. It took 3 days for the heel rash to appear, but only overnight for the instep. The instep rash was much more apparent and more itchy... but nothing like the forearm rash. [28]
    Not fun to walk on! ☹️ (Underside of the foot)[29]
    I find the itch to be more intense at the bottom of my feet compared to my forearm and the blisters feel like a burn. No pain on the forearm. [30]
    Never again! ☹️ (Underside of the foot) [31]
    I tried the underside on my foot about 2 months back - a TERRIBLE idea! The itching kept me up for most of the night. I’ve tried several creams but none really help. The feet was the only inoculation site that drove me that close to madness. It felt like somebody was tingling my feet with a feather for a full 4 days. I usually don't put any cream to relieve the itch when I inoculate and only use the hair dryer when necessary. But with the feet, I tried everything I had with the hope it would stop, but it didn't. Even the heel was terrible, it was like an "inside itch", because the skin is so much thicker, nothing really happens when you scratch it, it's like you cannot reach it. (Edited from this post.)
    One issue may be where your glabrous and non-glabrous skin border is. Basically where the fingerprint ends and regular skin starts. So if you do the arch (of the foot) it needs to be on fingerprint-like skin. I have tried this with mixed results and got lumps under the skin rather than ontop. [32]
    I’ve applied some to my foot below the inner ankle, same amount of rash and itching as any other spot! [33]
    I put mine on the instep/arch of my foot... No bumps, no itching. [34]
    I tried the instep and the itch was killing me. ☹️ [35]
    I tried the arch of my foot and found it to be much more tolerable… I didn’t get an itch or any bumps till 2 days after inoculating. I have a rash that’s under the skin but not painful and nothing has popped and oozed out. [36]
    I had huge fluid filled blisters in the arch of my foot when I applied NA there. They were painful but felt better after I pierced them to drain. I won’t do them on my feet again. The rash I get is always oozy, but easier to deal with on my arms. [37]
    I liked it on the top of my foot. [38]
    I have inocculated with NA and my foot was so swollen that I couldn't walk. ☹️ [39]
    I like to do ankles. [40]
    I’ve used my ankle for the first time which seems a LOT better than my arm or hip/upper thigh. [41]
    I did inside my ankle so I could scratch with the other foot. [42]
    3 days after inoculation i can barely walk...guess i shouldn’t have done it on my ankle. ☹️ [43]
    Worst rash I've had was on my arm, smallest on my ankle. [44]
    I have tried ankle/lower calf and it seems less sensitive than arm. Getting less of a reaction at innoculation site. [45]
    Calf. [46]
    I put them somewhere that isn't hard to scratch. Down on my calf I'd be bent over all day long. ☹️ [47]
    I've been inoculating into different areas on my knees. I have OA in my knees. No rash at all. [48]
    It always itches badly, but say the most sensitive places such as inner lower arm and inner calf (not to mention the hollow of the knee 😮 are "10" on the itching scale, then the middle of the thigh, or slightly above the knee, is "7" or "8"... [49]
    Inner thigh a few inches above my knee. [50]
    I use the front of my thigh. Easy to reach for scratching. [51]
    I did my second dose on my thigh and that worked fine. [52]
    I always used my thigh, but the rash kept getting worse and worse, and did leave faint scarring. [53]
    I usually use my arm and one time I tried using my leg and it was the ooziest, weepiest, itchiest I ever did. So I went back to using my arm. [54]
    I use somewhere on my legs because it's easier to hide under clothes. I always get an awfully itchy itch -- but slightly less when using the upper parts of the leg. [55]
    Top of the upper leg is best for me. Less visible. [56]
    Since it's summer, I think I'm going for left thigh or hip this time. [57]
    Fatty part of hip. [58]
    Hip was by far the worst. I had a terribly inflamed hard patch about the size of my hand for weeks. ☹️ [59]
    I always do my stomach. [60]
    So many friends use their belly, I thought I'd try it. Never again! [61]
    I tried my belly once but that gave me small pigmented scars. Mind this depends on your melanin levels. Was also very itchy btw. [62]
    I tried my belly last time. Holy Smokes Batman! That was a mistake. Horrible rash, itch. I still have marks over a month later. And still the occasional itching. Never again. [63]
    I've done my thigh but much prefer my arm as the itch seems more managable. [64]
    I always use the place on my inner arm halfway between my elbow and wrist, because it's flat and smooth... The forearm can easily be covered with a light sleeve but also quickly accessed for airing out or changing dressing. [65]
    I prefer the inner left forearm because I’m right handed and this makes applying anti-itch cream easier. [66]
    I switched to using the top of my forearm (trucker-tan area), instead of the soft under side of my forearm (because) I've found that if I inoculate on sensitive skin, I get all the rash. Underside nearly scarred. Topside, itch, yes, but visually invisible and not swollen. [67]
    I did 2 on my thigh then switched to my arm. I've found that the closer to my armpit, the faster it heals, and generally my arms heal faster than my legs. [68]
    I find the best place for me is the shoulder tip. [69]
    I started inoculating high on my shoulder because I sleep on my side, and that part is always squished against and rubbing around on the bed, and plus not very sensitive, so the itch is quite bearable. [70]

    One site that should be avoided is the thumb!

    When I was doing my inoculation, I accidentally dropped a drop of water onto my thumb and just wiped it off, but it was ridiculously painful the night I inoculated. Since then it's been like a big red boil - literally a throbbing cartoon thumb! Its been 6 days now and it's still kinda sore. I definitely don't recommend inoculation around the skin of the thumb nails! (Via private message.)

    Oral inoculation with NA is not effective

    There are several reasons why it is not recommended to swallow NA larvae.

    1. While oral inoculation has been shown to be effective with some hookworm species, such as the dog hookworm, Ancylostoma caninum, [71] and the human hookworm, Ancylostoma duodenale, [72] oral inoculation with Necator americanus has been found to be ineffective.

    N. americanus may require a period of growth in the lungs, which is not required by A. duodenale. This deduction is based on the observation that development of N. americanus following oral infection rarely succeeds and, even then, very few worms develop… the apparent inability of N. americanus to do this is thought to be attributable to an obligate pneumonic phase in its life history. [73]

    2. L3 hookworm larvae are particularly susceptible to acid, so there must be some developmental change that occurs during the few days that they normally take to travel from the skin to the stomach which enables them to survive the harsh, acidic gastric environment. Hotez and colleagues have reported that, following entry into the host via the skin, L3 larvae receive a signal present in mammalian blood and tissue that causes them to resume development and secrete bioactive polypeptides. [74] [75] Larvae that are swallowed will obviously not experience this trigger.

    3. Hookworms have probably taken the same route throughout most of their long co-evolution with mankind, so they are likely to try to follow the same pathway irrespective of where they actually enter the body. Therefore, unless they are encapsulated, larvae that are swallowed may still be looking for skin, and might mistake the lining of the mouth or throat for external skin and enter via these surfaces. Nagahana, et al., have reported that N. americanus L3 larvae will invade the buccal epithelium if they enter through the mouth. (Nagahana M, et al. Experimental studies on the oral infection of Necator americanus. III. Experimental infection of three cases of human beings with Necator americanus larvae through the mucous membrane of the mouth. Japanese Journal of Parasitology. 1963;12:162–167.) Since some people experience significant swelling at the inoculation site, there is a potential for blockage of the throat if larvae were swallowed.

    4. Oral inoculation does not provide the visible confirmation of dose viability that is common with successful percutaneous inoculation. So, unless the worms have been cultured by the person inoculating, or they have a microscope with which to check the viability of doses received from other sources, they might unknowingly swallow a dose of dead worms, which could delay the progress of their treatment.

    Possible side effects after inoculation with NA

    See the following pages.

    Checking whether inoculation was successful

    The success of inoculation can be confirmed in two different ways.

    1. A raised IgE level.

    If you had a full blood count (CBC) and/or IgE levels taken just before inoculation, you could retest a couple of weeks after the inoculation. If there has been an increase in eosinophils, this may suggest that colonisation has been successful, although there are other factors that can influence eosinophil levels.

    2. The presence of hookworm eggs.

    The presence of hookworm eggs provides definitive confirmation that there are mature hookworms in the gut, and egg production begins between 4 and 6 weeks after inoculation. Eggs can then be detected in either one of two ways.

    a) by having a stool sample professionally tested by a laboratory (see Stool testing)
    b) by incubating the individual’s stool and checking for hookworm larvae (see Helminth incubation)
    The best method I’ve found to track the condition of my colony is to incubate. (You can also try egg counting, but incubating seems a bit easier.) [76]

    Hookworm side effects

    See the following page.

    Hookworm timeline

    For what to expect in the days, weeks and months after inoculating with hookworms, see the following page.

    Hookworm lifecycle

    Hookworm LifeCycle.gif

    Source: US Centers for Disease Control [77]

    The developmental stages, migration and diet of Necator americanus

    Egg - Hookworms start their life as unembryonated eggs in faeces deposited in soil, and initially gain nutrients from the faeces. When there is adequate warmth, shade and moisture, the eggs embryonate and, within 1-2 days, hatch into first stage L1 larvae.

    L1 - In this first, non-infective, juvenile rhabditiform (free-living) stage, the larvae feed on bacteria living in the feces in which they were deposited [78] and on bacteria and organic debris in the soil until they molt, after approximately 3 days, into second stage larvae, L2s.

    L2 - During this second rhabditoform (free-living) stage, the L2 larvae will feed for 6 or 7 days and then molt again into third stage larvae, or L3s.

    L3 - In this infective, filariform stage, characterized by a closed mouth, the L3 larva does not feed in its natural environment and will only survive for a few weeks until it exhausts its lipid metabolic reserves, or it finds a host, at which point it will commence feeding on protein in the bloodstream. [79] [80]. The lifespan of L3 larvae supplied by commercial helminth providers may be further shortened by their exposure to the antibacterial rinse used by these companies to clean them.

    Once the L3 larvae have entered the skin, they remain inactive within the skin for about 40 hours before beginning to move into the cutaneous blood vessels and travel via the circulatory system and heart to the lungs, where there's another delay while further growth takes place in the alveoli. [81] The literature claims that the larvae reach the lungs at around 4-7 days. However, the subjective experience of NA self-treaters suggests an earlier migration through the lungs, with the L3s already ascending the bronchioles to the trachea - during which part of the journey they molt into the L4 stage - before day 4.

    Serum and gluthatione provide the signals for L3 larvae to continue their development to the L4 adult stage.

    In experimental conditions, exposure to serum has been shown to stimulate about 50% of hookworm L3s to feed and undergo development, and this response can be increased to 90-100% by adding glutathione to the serum. [82] Starting this process in a petri dish in larvae that are to be used in therapy would make infection impossible, but the serum experiment might indicate that L3 larvae are in fact able to feed once they enter the bloodstream, which might explain successful inoculations with old batches. [83]

    L4 - The L4 larvae transfer from the trachea to the oesophagus by slipping under the epiglottis. They are not necessarily coughed up into the mouth, as is sometimes claimed, unless they have become attached to mucus which is then coughed up. Once in the oesophagus, the larvae continue down to the intestines, which they reach, according to the literature, between days 8 and 14, but possibly much earlier, and perhaps even by days 4 to 7. They then molt into the pre-adult stage around days 17–21 and commence feeding on blood drawn from the intestinal mucosa. Any stragglers should all reach the intestine within 4 weeks.

    Contrary to the impression created in many scientific texts, the amount of blood drawn by Necator americanus is minuscule. When discussing the amount of blood lost to hookworms, researchers will often have in mind the Old World hookworm, Ancylostoma duodenale, which draws 9 times more blood than Necator americanus.

    L5 - At about 5-9 weeks, the larvae attain their adult (L5) form, fertilisation occurs, and the females begin producing eggs (5,000-10,000 per day per NA female) which are passed in the host's feces. [84] After 24–48 hours under favorable conditions, the eggs become embryonated and hatch. [85]

    Note. Many of the details above were recorded from observations in a hamster model. [86]

    Once it has reached the intestine, Necator never migrates to other parts of the body, so remains within the gut for the rest of its life, the length of which varies widely depending on the immune response of the individual host. (See Hookworm lifespan.)

    For more detail about the developmental stages and migration of NA in humans, see Immune responses following experimental human hookworm infection.

    Where hookworms live

    According to Wikipedia, mature Necator americanus live at the distal (lower) end of the jejunum and the proximal (upper) end of the ileum, while the other species of human hookworm, Ancylostoma duodenale - which is not currently used in therapy - resides in the duodenum/jejunum. [87]

    Croese, et al, used capsule endoscopy to determine that the distribution of NA was influenced by the parasite’s maturity, and that, early in infestation with NA, the worms were distributed along the length of the jejunum but that, by 20 weeks, the predominant location of surviving worms was the proximal jejunum - the upper end of the jejunum, just below the duodenum. [88] It could be argued that this latter observation is more likely to be correct than the opinion expressed in Wikipedia and, if it is, mature NA are most likely to be found where the red text appears in the following representation.

    mouth ➤ oesophagus ➤ stomach ➤ duodenumjejunumileumcaecumascending colontransverse colondescending colon ➤ rectum

    Rarely, NA have been observed in the stomach. This exceptional localisation might be caused by one of three factors:

    1. the removal of the jejunum and/or duodenum
    2. jejuno-duodeno-gastric reflux [89]
    3. an excessively large hookworm colony that has forced some of its members to spread out from their usual localisation site. [90]

    A short video clip of a hookworm in situ.

    While it is theoretically possible that NA might be seen during a colonoscopy, this would only happen if the colonoscope were advanced into the lower end of the ileum, and only if some hookworms had taken up residence there, which is unlikely unless the jejunum has been removed or very large numbers of NA - i.e., hundreds - are being hosted, forcing some NA to occupy the ileum. It is very unlikely that any would take up residence in the colon, which they normally only pass through after they die.

    Hookworms are not adversely affected by the laxatives used in preparation for a colonoscopy. While it is possible to lose hookworms to very severe diarrhoea/diarrhea, they can withstand the effects of normal, recommended quantities of laxative, including the standard colonoscopy prep.

    An upper endoscopy (i.e. via the mouth) will not reach past the second of the four parts of the duodenum, so will not usually reveal, or disturb, any hookworms unless these have been forced to spread beyond their usual location as a result of one of the three factors mentioned above.

    Caring for hookworms

    See the following page.

    Confirming hookworm infection

    There are three practical options for determining the presence of hookworms in the gut.

    1. Stool test

    From about six weeks post inoculation with hookworms, eggs will be detectable in the host's stool. Checking a stool sample for these eggs is the best way to establish whether hookworms are present. Unfortunately, while most pathology labs will have a faecal (stool) test called something like "Ova, Cysts, and Parasites" or "Ova and Parasite", they typically do not have sufficient experience to accurately identify hookworm eggs, a problem that is exacerbated by the relatively low numbers of worms used in helminthic therapy. Testing is therefore best carried out by a helminth provider who offers a stool testing service, a laboratory associated with a school of tropical medicine, a veterinarian (who will have experience with helminth eggs), or at home using a microscope and fecalyzer. For more details about these options, see the following page.

    2. Incubation

    Some hookworm hosts find it easier to check for the presence of worms by incubating a stool sample rather than attempting to count the eggs via a fecal float.

    3. Blood test for eosinophils

    Another way to determine whether or not you are hosting helminths is to have a blood draw to see if your eosinophil level is elevated. Although this is not a foolproof test for the presence of helminths, it is fairly reliable. It is also quick, and is a method that a medical insurer might pay for.

    Hookworm lifespan

    Once inside a host, NA are reported to survive for 3-10 years [91] [92] but to be capable of living for up to 15 years, [93] and possibly even 18 years. [94] However, the experience of hookworm self-treaters suggests that they typically only survive for approximately 1-3 years, and sometimes for as little as 2-3 months, depending on the strength of the individual host’s immune response. For more detail about this, see the following page section.

    Hookworm respiration

    Hookworms, like other nematodes, have digestive, nervous and reproductive systems but no circulatory or respiratory system. They pick up oxygen and give off carbon dioxide via the surface of their bodies using diffusion, which occurs whether they are in water or air. They are also able to extract oxygen from their host's blood. [95]

    Is there genetic degradation in laboratory-reared hookworms?

    Concern is sometimes expressed about the possibility that the Necator americanus larvae available within the helminthic therapy community may have become weakened as a result of genetic degradation. This concern focuses on two issues. Firstly, that deleterious mutations may emerge in the NA population and be propagated, thus weakening the stock. And, secondly, that the diversity of the stock may become restricted.


    Genetic degradation is not an automatic sequel to the restriction of a colony of microorganisms. Inbreeding does not have the same adverse consequences in all animals as inbreeding does in humans. In fact, some insect species are able to withstand the effects on their gene pool of high levels of inbreeding, and still produce healthy offspring - a feature seen in cockroaches and bed bugs. [96] Additionally, helminths have a particularly limited capacity for genetic alteration due to their size, as well as their prolonged life cycles and generation times when compared with smaller, simpler microbes, or ‘microparasites’. [97] When a single organism can lay thousands of fertilized eggs, as is the case with hookworms, the natural biology of that organism will make it resistant to the adverse effects of inbreeding.

    While the artificial selection of less healthy organisms might result in a weakening of the stock, in the case of helminthic therapy any loss of immune-modulating function in that helminth as a result of a mutation, would foreseeably result in that organism losing at least some ability to survive well inside the human body. Transfer of offspring to another host would therefore be less likely, compared to transfer of the offspring of an un-mutated sibling. In other words, the selection pressure for the traits desirable for therapy is maintained in the host, even in a setting where transfer from host-to-host is highly controlled.

    Results from one study comparing DNA sequences from NA that had been maintained for 100 generations in golden hamsters with the DNA from NA that were recovered from natural human infections [98] suggested that this particular laboratory strain of NA had undergone a severe genetic bottleneck. However, raising a human helminth in a laboratory rodent is an altogether different matter from maintaining the same species in humans. Over time, the helminth population in the rodent might adapt to that animal’s physiology via typical evolutionary processes.

    Loss of diversity

    Helminths in use for therapy undoubtedly lack genetic diversity compared with wild strains because a very limited number of organisms were selected and these have been propagated widely. However, there is no evidence to suggest any reduction of therapeutic effect over time from the NA stock that has been in use within the helminthic therapy community since 2007.

    There will inevitably be a similar lack of diversity in the even older stock being used by hookworm researchers in laboratories worldwide. Their NA samples were all obtained from Prof David Pritchard at Nottingham University, who collected his original sample from Papua New Guinea. While these researchers have the resources to obtain fresh samples from the wild, they have not done this, suggesting that any loss of diversity in their worms has not adversely affected these organisms’ natural attributes.

    Given all of the above, the possibility of an impairment in the domesticated NA stock due to genetic degradation is nothing that NA self-treaters need be concerned about. And, even if there were evidence of genetic degradation in laboratory-reared hookworms, there are no readly available solutions for addressing this.

    Risks involved in seeking alternatives

    Any attempt to obtain new stock from the wild would introduce a significant level of risk for anyone who was to host worms obtained in this way. Walking barefoot in open-air latrines is not a good idea, as has been explained by the only person who claims to have done this. [99] This activity introduces a risk of inadvertently acquiring a different type of helminth, such as the less desirable species of hookworm, Ancylostoma duodenale, which causes nine times more blood loss than NA, can be passed in a mother’s milk and can even cross the placenta to infect a foetus. Even more risky is the roundworm, Strongyloides stercoralis, which is autoinfective and potentially hyperinfective, with a risk of fatality. [100] [101]

    Since the eggs of both A. duodenale and S. stercoralis are virtually identical to those of NA, anyone attempting to obtain “wild” NA would need at least a very powerful microscope and a considerable level of expertise in species identification in order to be certain that they were not harbouring something much less desirable. They would also need to undertake multiple sequential terminations of their hookworm colony, followed by re-inoculation with individually selected larvae that had been definitively determined to be NA, either by a parasitologist with laboratory access, or by means of genetic testing.

    It may be possible to find alternative strains, of NA that have somewhat different immunomodulatory properties than the one currently in use. This would be akin to different breeds of dogs, or strains of E. coli that each interact much differently with humans even though they are all the same species. The only way to know if there are more effective helminths would be to approach the issue systematically with controlled clinical trials, and, so far, researchers have not even sampled many of the species that might be effective therapeutically. [102] (PDF)

    Also see: Comparing NA larvae from different sources.

    Can hookworms cause a positive result on fecal occult blood tests?

    Some hosts of NA have expressed concern that the minuscule amount of blood shed from hookworm feeding sites might cause a positive result on a faecal occult blood test. However, this is thought to be unlikely, especially given the poor sensitivity and specificity of stool guaiac tests.

    Is hosting NA contraindicated for someone with a gastric bypass?

    The hosting of hookworms does not present any risk to someone with a gastric bypass, and the surgery does not interfere with the hookworms’ ability to colonise and produce therapeutic effects.

    Although gastric bypass surgeries create a detour around, or reduce the volume of, the stomach, food is still able to pass through the reconstructed section of the intestine, and, at the point at which hookworm larvae travel through this section, they are still microscopic, so pass through easily. They then continue along the intestine and typically settle in the first part of the jejunum, which is some distance from the stomach. See Where hookworms live.

    Hookworm incubation

    See the following page.

    See also