Table 1.
List of different Brucella species and their natural hosts.*
| Brucella species | Colony type | Natural host** | Zoonoses | Year of first isolation |
|---|---|---|---|---|
| B. melitensis (bv1-3) | Smooth | Goat and sheep | +++ | Bruce (1893) |
| B. abortus (bv 1–6, 7, 9) | Smooth | Cattle | ++ | Schmidt (1901) |
| B. suis biovar*** | Huddleson (1929) | |||
| 1–3 | Smooth | Pig | ++ | |
| 2 | Smooth | Wild boar, Hare | + | |
| 4 | Smooth | Reindeer, Caribou | ++ | |
| 5 | Smooth | Rodent | – | |
| B. ovis | Rough | Sheep | –*** | Buddle (1956) |
| B. neotomae | Smooth | Desert rat | + | Stoenner and Lackman (1957) |
| B. canis | Rough | Dog | + | Carmichael and Bruner (1968) |
| B. ceti (B. delphini) | Smooth | Dolphins | + | Foster et al. (2007) |
| B. pinnipedialis (B. phocae) | Smooth | Seals | + | Foster et al. (2007) |
| B. microti | Smooth | Wild voles | (?) | Scholz et al. (2008) |
| B. inopinata | Smooth | Human | ++ | Scholz et al. (2009) |
| B. papionis | (?) | Baboons (Papio spp.) | (?) | Whatmore et al. (2014) |
| B. vulpis | (?) | Red foxes (Vulpes vulpes) | (?) | Scholz et al. (2016) |
| N.N.**** | Smooth | Frog | (?) | Soler-Lloréns et al. (2016) |
Different Brucella species and their natural hosts according to [4], [5], [7], [39], [41], [42], [43], [44], [45], [46].
The host susceptibility range of Brucella species is not extremely narrow. Nearly all Brucella species can infect other mammals beside their primary host with the exception of B. ovis. In such cases, the infection is mostly mild and even self-limiting.
Different B. suis biovars vary in their zoonotic potential, while biovars 1, 3 and 4 are more pathogenic to human than B. abortus but less than B. melitensis, other B. suis biovars have obviously limited potential to infect humans. The reason why the B. ovis is not zoonotic in opposite to the rest of Brucella species is attributed to the fact that the genome of B. ovis contains a high percentage of pseudogenes and other mobile genetic elements compared to the rest Brucella species due to genome degradation in parallel with narrowing of the host susceptibility scope of B. ovis. This genomic degradation and re-arrangement lead to the deletion of the genomic island 2, which is responsible for lipopolysaccharide biosynthesis in addition to the inactivation of essential genes regulating nutrient uptake and utilization. All of these factors, beside the inactivation of genes responsible for the synthesis of the envelop outer membrane proteins, lead to the loss of the ability of B. ovis to invade humans and many other mammalian species [25].
An intermediate trait between the soil associated ancestor of Brucella species and the known host adapted Brucella species. No data are yet available about its zoonotic capability.