Brucellosis Contagious?

this whole area is tricky - mainly due to lack of research

however - in the case of brucellosis we know it is spread to humans from the fluids of infected animals and even aerosols of these fluids - this is typically how vets and farmers get infected - eg when lambing or calving - it is also known to enter through open wounds and even through mucous membranes which can be how butchers or hunters contract it - so i would say there is a very good chance it can be sexually transmitted.

the CDC site is typically pretty conservative - but gives us the basic picture
https://www.cdc.gov/brucellosis/transmission/index.html

its is very closely related to another bacteria called bartonella - and i suspect this can be transmitted via similar pathways. my partner and i both have it along with Lyme - and we don't know how we came to be infected for certain - we were both bitten by many horseflies on a picnic in farmland - that could have infected both of us - but its also possible one gave it to the other unknowingly

i wish there were more data on this

perhaps worth adding to the thread with what we know on the main infections we are dealing with

lyme -
-same groups as syphilis which we know is sexually transmitted and very contagious

-since it is spread by biting insects - any activity that exposes one to blood of an infected person could be a means of infection - especially if in contact with broken skin and possibly mucosal membranes note sex can include tiny breaks tears or abrasions in skin for either partner due to friction or stretching.

-LLMD's report something in the order of 1in 10 to 1in 5 of thier patients who are in couple relationships has a partner who is ill with same/ similar disease
small PCR studies have been done that show that in such cases the strain of lyme in both partners is most often identical - meaning they were either both infected by the same source ( less likely - as hundreds of strains in nature and a single tick does not bite two people) or one infected the other.

-is also known to cross the placenta into the foetus in a significant proportion of pregnancies
( LLMDs often try to reduce this from occurring via treating the mother with antibiotics to reduce pathogen load and activity during pregnancy)

the immune system - its condition and health are major factors determining is an exposed individual becomes ill or not - and it may well be that the transmissivity or contageousnous of lyme is being underestimated because partners that are infected may not show obvious signs of disease - due to their immune systems holding the infection under control.
note- many lyme patients also do not get ill at the time of their tick bite / infection - but later after a life stressor lowers their immune systems ability to function and the stealth pathogens are able to get a foothold.