Routes of transmission have traditionally been classified as vector-borne (ie-biting insects like fleas, sand flies or human lice), or secondary to a cat bite or scratch, typically associated with the presence of fleas. Over the last few decades, additional routes of transmission have been discovered.
Below are helpful publications discussing newly discovered routes of potential transmission.
The research is evolving and much more is needed but implicate the following:
Animal Saliva
Perinatal Transmission
Newly Identified Vectors
Needle Stick Transmission in a Veterinarian
Blood Transfusions (Bartonella remains viable during long-term storage of Red Blood Cell Units)
Animal Saliva-Cat Bite Transmission:
"Nearly all patients with cat scratch disease report contact with cats, most of which are healthy. The specific location of the organism in the cat is unclear with periods of asymptomatic bacteremia occurring in cycles. The infection is transmitted to humans through a bite or scratch."
Bartonella henselae Antibodies after Cat Bite. Emerging Infectious Disease, 2008
Detection of Bartonella henselae in domestic cats' saliva. Iranian Journal of Microbiology, 2010
Isolation of Bartonella quintana from a woman and a cat following putative bite transmission. Journal of clinical microbiology, 2006
Cat Scratch Disease and Arthropod Vectors: More to it than a Scratch? Journal of the American Board of Family Medicine, 2010
Detection of Bartonella henselae in domestic cats' saliva. Iranian Journal of Microbiology, 2010
Zoonotic Disease: What Can I Catch from My Cat? Cornell University Feline Health Center, 2017
Cat Scratch Disease and Arthropod Vectors: More to it than a Scratch? Journal of the American Board of Family Medicine, 2010
Perinatal Transmission:
Sadly, transplacental transmission of Bartonella species occurs commonly in naturally and experimentally infected rodents. Compounding data suggests that Bartonella can undergo vertical transmission in humans.
In general, 'Vertical Transmission' means that an infection/pathogen uses the intimate nature of pregnancy to transmit disease directly from mother to- an embryo, fetus, during childbirth or to the baby during pregnancy. Vertical Transmission typically occurs when the mother has a pre-existing disease or becomes infected during pregnancy.
During pregnancy, an infection with Bartonellosis has often been related to serious maternal or fetal complications (including miscarriage, fetal death, or premature delivery. It has also brought into question transmission via breastfeeding. This reinforces the need for early detection and treatment of infected pregnant women. Bartonella has a slew of symptoms and co-morbidities in children, many of which are neuropsychiatric. I have only started to brush the surface of this data and it is very unsettling, especially for someone who wants to have children but is currently infected with Bartonellosis. That being said, anecdotally, many women who have been diagnosed and successfully achieved remission with appropriate treatment for Bartonella have been able to have healthy babies to term with no obvious onset of clinical illness.
Molecular Evidence of Perinatal Transmission of Bartonella vinsonii subsp. berkhoffii and Bartonella henselae to a Child. Journal of Clinical Microbiology, 2010
Possible Vertical Transmission of Bartonella bacilliformis in Peru. The American Journal of Tropical Medicine and Hygeine, 2015
New Vectors:
A vector is a living organism (insect) that can transmit infections (parasites, viruses or bacteria) between humans and animals or from animals to humans (known as Vector-Borne Disease).
"Vector transmission of bartonella occurs via two primary routes: 1) Inoculation of Bartonella contaminated arthropod feces (ie flea poop) via animal scratches, most often cat scratches, or 2) by self-inflicted contamination of wounds induced by the host scratching arthropod bites [172]". Typically, while an insect is feeding on a host (the animal or human), it's simultaneously digesting it's meal (ie- having a bowel movement) which leaves infected feces in the area of the bite. As we have all experienced, bites tend to itch. The natural response is to scratch the area in an attempt to soothe the itch (which only makes it itch more). During this process the animal or human moves the infected insect feces onto the bite and/or scratches themselves deep enough to break the skin -- this introduces the bartonella bacteria to the blood stream ("inoculation and self-inflicted contamination").
The most notable insects in the transmission of bartonella are the cat flea, human louse and sand flies, however, new vectors (such as a spider, horse fly, tick and possibly bed bug) have been identified as potential transmitters.
Potential for Tick-borne Bartonelloses. Emerging Infectious Disease, 2010: ** “Since the submission of this manuscript, we found 3 cases of B. henselae infection transmitted by Dermacentor spp. Ticks”**
Identification of Novel Zoonotic Activity of Bartonella spp., France. Emerging Infectious Disease, 2016
Case Reports Suggest Spiders, Red Ants, Kissing Bugs and Mites are capable of potential transmission" Galaxy Diagnostics Suspected Insect and Arthropod Vectors for Bartonella, 2019.
Blood-to-Blood Transmission:
[1] Needle Stick Transmission in Veterinarians:
Suspected Needle Stick Transmission of Bartonella vinsonii subspecies berkhoffii to a Veterinarian. Journal of Veterinary Internal Medicine, 2010
Unknown Fever and Back Pain Caused by Bartonella henselae in a Veterinarian After a Needle Puncture: A Case Report and Literature Review. Vector-Borne and Zoonotic Diseases, 2011
[2] Transfusion Transmission:
Bartonella can cause a chronic, sub-clinical infection, sometimes without any symptoms. That makes it possible for someone with Bartonella (despite displaying minimal or no symptoms) to readily donate if they feel healthy. This poses a hazard for blood recipients because donors are not typically screened for Bartonella infections. Additionally, Bartonella can survive long-term in multiple types of blood products. Bartonella's profile typically evades direct PCR detection thus the safety of the blood (in regards to Bartonella) cannot be guaranteed by standard screening performed on blood products. This has been well established in animal models involving mice, even when the donor animals have undetectable blood stream infection.
If you are a Bartonella or Lyme patient, or someone suffering from Vector-borne disease, the recommendation is to not donate blood or be an organ donor. Human blood transmission has already been documented and solid organ transplant recipients can also be infected by Bartonella spp. that may result in fatal outcomes.
Bartonella henselae survives after the storage period of red blood cell units: is it transmissible by transfusion? Journal of Transfusion Medicine, 2008
Infectious agents, Leptospira spp. and Bartonella spp., in blood donors from Cajamarca, Peru. Journal of Blood Transfusion, 2016
Long time survival of Bartonella bacilliformis in blood stored at 4 °C. A risk for blood transfusions. Journal of Blood Transfusion, 2012
Bartonellosis as cause of death after red blood cell unit transfusion. Ultrastructural Pathology, 2009
Pathogens transmitted in red blood cell transfusions: An up-to-date table (listing viruses, bacteria, protozoa and prions) Baylor University Medical Center, 2018
Bartonella henselae transmission by blood transfusion in mice. Transfusion, 2016
"It is important to highlight the presence of asymptomatic people, who account for about 45% of the population in some endemic areas; consequently, the risk of transfusion transmission is of note, especially because of the ability of B. bacilliformis to survive in blood stored at 4 ºC for up to 1 year"- [Citing Article].
Below is a chart of pathogens capable of being transmitted in Red Blood Cell Transfusions | Bartonella is NOT part of the human donor screening for Infectious Disease
1.0 CME. This module provides an overview of key vectors and modes of transmission associated with Bartonella spp. infection, with special attention to ongoing debates surrounding tick transmission, perinatal transmission, and other modes, like transfusion and needlesticks.