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Schistosomiasis increases risk of infection with HIV, especially for women and is also associated with a higher HIV viral load
Michael Carter, 2017-11-20 06:50:00
Infection with schistosome
parasitic worms has an important role in HIV transmission, especially for
women, and may accelerate HIV disease progression, according to research
published in PLOS Neglected Tropical
Diseases. Women with schistosomiasis
had a three-fold increased risk in becoming infected with HIV, compared to
women who did not carry the worms. Moreover, HIV viral load after infection was
higher among schistosome-infected individuals, increasing both their potential
infectiousness to sex partners and the risk of HIV disease progression.
suggests that interactions exist between HIV-1 and schistosomiasis that may
play a critical role in HIV-1 transmission and disease progression in African
countries,” comment the investigators.
a disease caused by a tropical parasitic worm infection. Over 90% of infections
occur in Africa. The worms live in small veins in host’s pelvis and gut and
daily lay hundreds of eggs that migrate to the urogenital and gastrointestinal
mucosa where they cause inflammation and physical breaches in the mucosa.
A team of
investigators postulated that pre-existing schistosome infection would increase
a patient’s risk of acquiring HIV, with the risk especially high for women. They
also hypothesised that individuals with active schistosome infection at the
time of HIV acquisition would have impaired immune systems, resulting in higher
HIV viral loads.
To test these
hypotheses, the researchers designed a nested case-controlled study involving adults
living in rural Tanzania. In 2007, 2010 and 2013 participants were tested for
identified 73 individuals who became infected with HIV during follow-up. These
people were matched with 265 controls who remained HIV negative. Dried blood
spots from the cases and controls were tested for the presence of schistosome
infection to see if it increased the risk of acquiring HIV.
also compared the viral loads of HIV seroconverters according to
In women, 44% of
those who acquired HIV had schistosome infection at the time of their
seroconversion compared to 30% of the HIV-uninfected controls. After taking
into account potential confounders, the investigators showed that women with
schistosome infection had an almost three-fold increase in the risk of becoming
infected with HIV compared to women who remained HIV negative (OR = 2.8; 95%
CI, 1.2-6.6, p = 0.019).
Just under a third
(29%) of men who seroconverted for HIV had schistosomiasis at the time they
became infected with HIV, compared to a schistosomiasis prevalence of 38% among
men who remained HIV negative. As such, the schistosome infection did not
increase the risk of HIV acquisition for men.
“We found that
schistosomiasis increases the odds of HIV-1 acquisition in women but not men,”
comment the researchers. “This strong gender effect may be due to differential
effects of schistosome eggs in the genital mucosa of women versus men.”
Among people who
did become infected with HIV, median viral load was approximately 25,000
copies/ml among those with schistosomiasis compared to 5000 copies/ml among individuals who did not carry the parasitic infection, a significant difference (p
= 0.017). Viral load differences by schistosomiasis-infection status were more
pronounced in women.
“We found that
schistosomiasis at the time of HIV-1 infection led to a 0.7 log10
increase in viral load at the time of HIV-1 seroconversion,” write the authors.
“A sustained 0.7 log10 HIV-1 load increase equates with an
approximate doubling of infectivity among HIV-1-schistosome co-infected
individuals and would be expected to accelerate time to symptomatic AIDS or
death by 2-3 years.”
The authors conclude
that schistosomiasis increases HIV incidence among women and raises viral load
at the time of seroconversion. They note that praziquantel is a cheap and safe
treatment for schistosomiasis and call for studies to determine the
effectiveness of mass therapy with this drug to decrease HIV transmission and
slow HIV disease progression.