Certain parasitic infections can raise blood pressure in specific parts of the body, particularly in the blood vessels of the lungs and liver. But the link between parasites and the kind of high blood pressure most people worry about, the systemic type measured with a cuff on your arm, is much weaker than you might expect. The relationship is complex, and for some parasites, the evidence actually points in the opposite direction.
Schistosomiasis and Pressure in the Lungs and Liver
Schistosomiasis is the parasitic infection most clearly tied to high blood pressure, but not the systemic kind. This waterborne parasite, which affects over 200 million people worldwide across 74 countries, causes problems by lodging its eggs in the liver and lungs over time. In the liver, repeated waves of eggs trigger a scarring pattern called periportal fibrosis that blocks blood flow through the organ’s portal vein system. The result is portal hypertension: dangerously high pressure in the veins connecting the gut to the liver. This can lead to an enlarged spleen, swollen veins in the esophagus, and life-threatening internal bleeding.
Unlike liver cirrhosis from alcohol or hepatitis, schistosomiasis preserves overall liver function. The liver cells themselves remain healthy. But the plumbing gets blocked, and the body compensates by creating new, fragile blood vessel pathways that can rupture.
The lungs are the other major target. Roughly 5 to 30% of people with the advanced hepatosplenic form of schistosomiasis develop pulmonary arterial hypertension, where pressure builds in the blood vessels feeding the lungs. Studies from Brazil put that figure at 7.7 to 10.7%, while historical Egyptian data reported rates of 7.7 to 18.5%. One study in the Nile Delta found that 8.6% of previously infected, symptom-free residents had elevated pulmonary artery pressure. Globally, an estimated 4 to 10 million people may have pulmonary hypertension tied to schistosomiasis, making it one of the leading infectious causes of this condition. The parasite triggers intense inflammation in lung blood vessels through signaling molecules like IL-6 and TNF-alpha, which promote vessel wall thickening and remodeling over time.
Malaria’s Inflammatory Effect on Blood Vessels
Malaria is the parasitic infection researchers have most actively investigated for a link to standard, systemic hypertension. The theory centers on chronic inflammation. Repeated malaria infections flood the body with inflammatory signals that could, over time, damage blood vessel walls and increase their stiffness. One proposed pathway involves a protein called hepcidin that the body overproduces during malaria-related inflammation. Hepcidin locks iron inside cells, creating a functional iron deficiency that disrupts the normal elasticity and function of blood vessels. Arterial stiffness and elevated blood pressure have both been linked to high hepcidin levels.
The hypothesis is plausible, but the evidence remains indirect. Most published research has speculated about this connection rather than proving it in large human studies. Researchers have called for cohort studies in regions like sub-Saharan Africa and India where both malaria and hypertension are common, but those definitive studies haven’t been completed yet. Interestingly, acute malaria infections can push blood pressure in the other direction entirely. Orthostatic hypotension, a sudden drop in blood pressure when standing, is well documented in both the most dangerous form of malaria (caused by P. falciparum) and the milder P. vivax form. The parasite disrupts the autonomic nervous system’s ability to tighten blood vessels and speed up heart rate in response to position changes.
Chagas Disease and the Nervous System
Chagas disease, caused by a parasite spread through the bite of triatomine (“kissing”) bugs in Latin America, damages the heart and the nerves that regulate it. In people who have both Chagas disease and hypertension, research shows significantly impaired parasympathetic nervous system function, the branch responsible for slowing the heart and keeping blood pressure in check during rest. These patients show reduced heart rate variability and a blunted response when shifting from lying down to standing.
This doesn’t mean the parasite directly causes hypertension. Rather, Chagas disease appears to strip away one of the body’s built-in blood pressure control mechanisms. For someone already at risk of high blood pressure, the loss of that protective nerve signaling could make the condition harder to manage and more volatile.
Toxoplasma: A Surprising Counterexample
If you’ve come across claims that the common parasite Toxoplasma gondii (carried by cats and found in undercooked meat) raises blood pressure, the data tells a different story. A large study of U.S. adults found that people who tested positive for prior Toxoplasma infection actually had lower blood pressure. After adjusting for age, weight, income, and other factors, infection was associated with about 1.3 points lower systolic pressure and 0.9 points lower diastolic pressure. People with Toxoplasma antibodies also had a reduced probability of being classified with Stage 1 or Stage 2 hypertension. The reasons aren’t fully understood, but the finding runs directly counter to the idea that this parasite drives blood pressure up.
What Treating the Infection Does to Blood Pressure
One way to test whether parasites truly cause high blood pressure is to treat the infection and see if pressure drops. A systematic review examined three studies that did exactly this, and the results were consistently negative. A large prospective study found no blood pressure differences six months after treating a liver fluke infection with standard antiparasitic medication. A randomized trial treating mixed worm infections showed no change at 52 weeks. A third trial followed patients with heavy schistosomiasis for four years after treatment and found no effect on blood pressure, though reinfection rates remained high in both groups, complicating the interpretation.
Some studies have even found that certain worm infections are associated with slightly lower blood pressure. One trend noted in the research was that heavy schistosomiasis infection correlated with lower diastolic blood pressure compared to uninfected individuals. This fits with a broader theory in parasitology: some chronic worm infections may actually dampen the immune system’s inflammatory activity in ways that lower cardiovascular risk, at least for systemic blood pressure.
Portal and Pulmonary vs. Systemic Hypertension
The critical distinction most online sources miss is between types of hypertension. When your doctor checks your blood pressure, they’re measuring systemic arterial pressure. Parasites have not been convincingly shown to raise this number. What parasites can do, particularly schistosomiasis, is raise pressure in specific vascular beds: the portal system (liver) and the pulmonary arteries (lungs). These are serious, sometimes fatal conditions, but they don’t show up on a standard blood pressure reading. Pulmonary hypertension requires an echocardiogram or specialized catheterization to detect, and portal hypertension is diagnosed through imaging and clinical signs like an enlarged spleen or esophageal varices.
A filarial worm called Wuchereria bancrofti, which causes lymphatic filariasis (elephantiasis), has also been linked to pulmonary hypertension, though the mechanisms are not yet well understood. This further reinforces the pattern: parasites seem to affect localized vascular pressure far more than the body-wide arterial pressure most people mean when they ask about “high blood pressure.”
The Bottom Line on Parasites and Blood Pressure
If you’re dealing with unexplained high blood pressure and wondering whether a hidden parasite could be the cause, the current evidence suggests it’s unlikely for standard systemic hypertension. The inflammatory pathways are biologically plausible, especially with repeated malaria exposure, but no study has yet demonstrated a clear, consistent causal link. For pulmonary and portal hypertension, the story is different. Schistosomiasis is a recognized cause of both, and anyone with a history of exposure to contaminated freshwater in endemic regions of Africa, Brazil, the Middle East, or Southeast Asia who develops shortness of breath or signs of liver congestion should have that history taken seriously in their workup.