Allicin and diallyl disulfide have direct experimental evidence against Babesia. The other six below have antibacterial evidence. This is a research-priority list only.
1. Allicin—diallyl thiosulfinate
Evidence: antibacterial activity, Babesia cultures, and a Babesia mouse model.
Allicin inhibited B. bovis, B. bigemina, and B. caballi, with respective IC₅₀ values of 818, 675, and 470 µM. It also reduced B. microti parasitemia in mice. These relatively high culture concentrations and parasitemia reduction do not establish human efficacy or sterilizing cure. A separate study demonstrated antibacterial activity against clinical MRSA isolates.
References:
Salama AA, AbouLaila M, Terkawi MA, Mousa A, El-Sify A, Allaam M, Zaghawa A, Yokoyama N, Igarashi I. Inhibitory effect of allicin on the growth of Babesia and Theileria equi parasites. Parasitology Research. 2014;113(1):275–283. doi:10.1007/s00436-013-3654-2.
Cutler RR, Wilson P. Antibacterial activity of a new, stable, aqueous extract of allicin against methicillin-resistant Staphylococcus aureus. British Journal of Biomedical Science. 2004;61(2):71–74. doi:10.1080/09674845.2004.11732646.
2. Diallyl disulfide—DADS
Evidence: direct activity against B. duncani in culture.
In a hamster-erythrocyte culture model, DADS had an IC₅₀ of approximately 46 µM, or 6.7 µg/mL. DADS combined with azithromycin prevented regrowth under the study’s subculture conditions—a stronger endpoint than growth inhibition alone, although still an in-vitro result. DADS is chemically distinct from allicin.
Reference:
Zhang Y, Bai C, Shi W, Alvarez-Manzo H, Zhang Y. Identification of essential oils including garlic oil and black pepper oil with high activity against Babesia duncani. Pathogens. 2020;9(6):466. doi:10.3390/pathogens9060466.
3. Diallyl trisulfide—DATS, also called allitridin
Evidence: antibacterial activity against S. aureus, including MRSA.
In a direct comparison of four diallyl sulfides, DATS had greater antimicrobial activity than DADS and diallyl monosulfide. I did not identify a direct Babesia study of purified DATS; findings for other protozoa cannot establish anti-Babesia activity.
Reference:
Tsao SM, Yin MC. In-vitro antimicrobial activity of four diallyl sulphides occurring naturally in garlic and Chinese leek oils. Journal of Medical Microbiology. 2001;50(7):646–649. doi:10.1099/0022-1317-50-7-646.
4. Ajoene
Evidence: direct antibacterial inhibition and killing.
Ajoene inhibited several Gram-positive bacteria at 5–20 µg/mL, while tested Gram-negative organisms generally required higher concentrations. Growing Bacillus cereus cells were killed at 30 µg/mL after 24 hours under the reported conditions. Resting cells required substantially higher concentrations. No direct Babesia evidence was identified.
Reference:
Naganawa R, Iwata N, Ishikawa K, Fukuda H, Fujino T, Suzuki A. Inhibition of microbial growth by ajoene, a sulfur-containing compound derived from garlic. Applied and Environmental Microbiology. 1996;62(11):4238–4242. doi:10.1128/AEM.62.11.4238-4242.1996.
5. Diallyl tetrasulfide—DATTS
Evidence: strong comparative antibacterial activity in vitro.
DATTS was the most active of the four diallyl sulfides in the Tsao–Yin comparison: tetrasulfide > trisulfide > disulfide > monosulfide. This assay-specific ranking does not establish superior clinical efficacy. No direct Babesia evidence was identified.
Reference:
Tsao SM, Yin MC. In-vitro antimicrobial activity of four diallyl sulphides occurring naturally in garlic and Chinese leek oils. Journal of Medical Microbiology. 2001;50(7):646–649. doi:10.1099/0022-1317-50-7-646.
6. Diallyl sulfide—DAS, or diallyl monosulfide
Evidence: antibacterial activity and documented bacterial injury.
Experiments with Cronobacter sakazakii demonstrated antimicrobial effects accompanied by changes in protein structure, gene expression, and cell morphology. It is generally less potent than longer-chain diallyl polysulfides in comparative assays. No direct Babesia evidence was identified.
Reference:
Feng S, Eucker TP, Holly MK, Konkel ME, Lu X, Wang S. Investigating the responses of Cronobacter sakazakii to garlic-drived organosulfur compounds: a systematic study of pathogenic-bacterium injury by use of high-throughput whole-transcriptome sequencing and confocal micro-Raman spectroscopy. Applied and Environmental Microbiology. 2014;80(3):959–971. doi:10.1128/AEM.03460-13.
7. Dimethyl trisulfide—DMTS
Evidence: antibacterial activity against enteric bacteria.
Purified DMTS inhibited six tested enteric isolates, with 24-hour MICs of 0.02–0.31 mg/mL. It was more active by mass than the diallyl-sulfide mixture used in that experiment. This does not establish achievable therapeutic blood concentrations. No direct Babesia evidence was identified.
Reference:
Ross ZM, O’Gara EA, Hill DJ, Sleightholme HV, Maslin DJ. Antimicrobial properties of garlic oil against human enteric bacteria: evaluation of methodologies and comparisons with garlic oil sulfides and garlic powder. Applied and Environmental Microbiology. 2001;67(1):475–480. doi:10.1128/AEM.67.1.475-480.2001.
8. Allyl methyl sulfide—AMS
Evidence: narrower antibacterial evidence against a veterinary pathogen.
Purified AMS impaired Actinobacillus pleuropneumoniae in vitro. The accompanying pig experiment used dietary garlic, so its animal results cannot be attributed to purified AMS alone. This is a lower-priority candidate than the compounds above, and no direct Babesia evidence was identified.
Reference:
Becker PM, van Wikselaar PG, Mul MF, Pol A, Engel B, Wijdenes JW, van der Peet-Schwering CMC, Wisselink HJ, Stockhofe-Zurwieden N. Actinobacillus pleuropneumoniae is impaired by the garlic volatile allyl methyl sulfide (AMS) in vitro and in-feed garlic alleviates pleuropneumonia in a pig model. Veterinary Microbiology. 2012;154(3–4):316–324. doi:10.1016/j.vetmic.2011.07.011.
For Babesia specifically, DADS and allicin deserve the closest examination. The cited studies do not establish an effective human dose, and garlic oil, allicin preparations, and aged garlic extract cannot be treated as chemically interchangeable products.