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PARASITES and RESEARCH 1
 Blastocystis hominis cyst-like forms stained in trichrome.
The sizes vary from 4 µm to 10 µm.
(Image library CDC, Center for Disease Control And Prevention, Atlanta)
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INTRODUCTION
BLASTOCYSTIS HOMINIS
GIARDIA LAMBLIA
CRYPTOSPORIDIUM AVIUM
INTRODUCTION
A fantastic story about the complexity of a parasites-lifecycle:
Dicrocoelium dendriticum (lancet fluke) lives in the soil and grass and finishes its life cycle in the bile tract of cattle, sheep, pigs, goats and in very rare occasions humans. It can easily end up as snail food. But snails cannot digest the littles fluke eggs. They end up in the snail's faeces and are then taken up by ants Formica fusca. Most encyst in the abdomen of the ant, but very few migrate to the head of the ant. They do not infect, but alter the behaviour of the ant. When the temperature drops in the evening, the infected ants do not return to their nests, but climb to the top of the vegetation and clamp on to the leaves with their mandibles. They stay there immobile until the next morning. When the temperature warms up the ants then resume there normal behaviour. This very strange behaviour places the ants in a region where they are likely to be eaten by browsing herbivores, which tend to eat late in the evening or in the early morning. Once eaten by the third host they migrate up the bile duct to the liver where they can cause severe biliary disfunction.
PARASITES and RESEARCH 1 #02
Blastocystis hominis
BLASTOCYSTIS HOMINIS
INTRODUCTION:
first of all, you cannot see this parasite with your naked eye!
# Originally believed to be a yeast, Blastocystis hominis was finally recognised as a protozoan by Zierdt in 1967 and reclassified under the subphylum Sporozoa.
# B.hominis lacks a cell wall but possesses a membrane-bound central body, as well as mitochondria of protozoan morphology.
# B. hominis exhibits pseudopod extension and retraction and reproduces by binary fission or sporulation.
# B. hominis is a strict anaerobe and requires the presence of bacteria for growth. Optimal growth of this organism occurs at neutral pH at 37｡C.
# Blastocystis is an intestinal microscopic parasite that is present not only in humans but also in a wide range of animals, including pigs, chickens, rats, and even cockroaches.
# When Blastocystis is isolated from a human it is known as Blastocystis hominis despite genetic analysis showing that many infections occur from different species in the Blastocystis genus.
# Often found as part of the normal gut fauna Blastocystis is frequently overlooked as a parasite when patients display signs of illness.
The very nature of Blastocystis as a disease causing agent is still in question.
ECOLOGY:
# Summarizing current data, B. hominis infections do not appear to be restricted by climate conditions, socio-economic groups, geographical area
# Blastocystis occurs in flies, worms, reptiles, birds and mammals.
# Differences in proteins and DNA suggest there is more than one species of the protozoan in humans.
# Transmission routes so far established:
- oral-faecal route (esp. within families, communities without adequate sanitary facilities, children day-care centres, hospitals)
- waterborne via untreated water or poor sanitation
- therefore: food-borne
B. hominis seems to have a stronger effect when together with other bacteria and fungi
It is also suggested that cockroaches act as vectors.
EPIDEMIOLOGY:
# Blastocystis hominis is often found in the colon as part of what may be considered the normal gut fauna and its links to disease are still considered controversial. This makes the study of its epidemiology difficult.
# Although there have been many surveys, most of these are conducted on patients already displaying symptoms and as such may be considered bias when compared to random surveys.
# B. hominis is ubiquitous world-wide. Reported prevalence ranges from 2-50% and is highest where hygiene is poor.
# There appears to be no seasonal affect on infection rates.
# Equal numbers of females and males are infected.
# Infection appears to be more common in adults than in children. However, one study showed a peak at around 10 years of age and then a second peak much later life.
# In some studies, the prevalence of B. hominis in patients with gastrointestinal symptoms was not significantly different from that found in control populations.
# Travel history (to undeveloped countries) has been implicated as a risk factor.
CLINICAL MANIFESTATION:
Many symptoms are associated with Blastocystis hominis. That makes this parasite a "diagnostic favourite" (like Candida!) for some practitioners.
Here are some reported symptoms:
# Profuse watery diarrhoea
# In 10% of cases constipation
# Abdominal pains, cramps, discomfort
# Nausea
# Fatigue
# Flatulence
# Anorexia
# (occasionally) fever
# Cutaneous rashes and itching
# Joint pains and swelling
# Faecal leukocytes
# Rectal bleeding
# Hepatomegaly
# Spleenomegaly
It is difficult to ascertain that B. hominis is the actual cause of all theses symptoms, because They are not specific to Blastocystosis, but are common in many other infections caused by other protozoa. bacteria, fungi and viruses.
TREATMENT:
# There is no specific treatment, because multiple infections or other concomitant factors are required to establish a B. hominis infection
some physicians believe that chemotherapy is necessary
# Some physicians believe that B. hominis is only strong when other bacteria and/or fungi are out of control within the patient’s body (Dysbiosis)
# <>Some physicians consider the infections self limiting
# No treatment is suggested when the parasite is found in stool, but no symptoms occur
# Anti-protozoan drugs:
Metronidazole – often used but reports suggest that it is ineffective (drug resistance? inactivation by concomitant organisms? Pharmacokinetic properties?)
Iodoquinol – (300mg 3x/d 10days – 650mg 3x/d 20days) Countries taking it off the market because of its toxicity and severe side-effects.
More than 42 other drugs are under development to inhibit the growth of B. hominis
# Antibiotics and antifungal agents do not inhibit growth but are commonly used to kill other microbes which seem always to appear with the protozoan.
Herbal treatments include black walnut, cloves, carvacrol oil (oregano), Allium sativum, Lonicera japonica, zinc, vitamin A retinol/betacarotene, pure ascorbic acid (vit. C) (herbal enemas are often used)
# Because B. hominis seems to have a fatty reservoir, fat splitting/fat-digesting enzymes are important.
# Dietary management through high fibre intake and elimination of smoked, cured and fermented foods/drinks. |
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