Belize Ticks: Ehrlichia Carriers

In Belize, ticks carrying the Rickettsia bacteria, which causes spotted fever, have been found on wild mammals in natural areas. The ticks were collected from the animals and identified as Amblyomma ovale, Amblyomma coelebs, Amblyomma pacae, Amblyomma cf. oblongoguttatum, and Ixodes affinis. Three rickettsial agents were detected: Rickettsia amblyommii in A. pacae, Rickettsia sp. strain Atlantic rainforest in A. ovale, and Rickettsia sp. endosymbiont in Ixodes affinis.

Amblyomma ovale

The immature stages of A. ovale feed mainly on birds and small rodents, while adults feed on wild carnivores, as well as domestic dogs and humans. The species has been implicated in the transmission of Rickettsia parkeri, the causal agent of human spotted fever, in South America and Mexico.

A. ovale is characterised by a hypostome with 3/3 dentition, a coppery brown shield with greenish spots, marginal and large eyes, a small, shallow, and punctuated basis capituli, and two very long spurs on coxa I, with the external one being slightly longer than the internal one.

In terms of geographical distribution, A. ovale has been found in various environments in Panama, from lowlands to places with altitudes of up to 800m, including rural towns, disturbed forests, and wilderness areas. In Brazil, the species has been found at altitudes ranging from 98 to 1220m above sea level, with a preference for lower altitudes.

The first record of A. ovale in the state of Oaxaca, Mexico, was in 2022, when an adult engorged female was found on a bloodhound dog. This finding suggests that the species may be extending its range due to factors such as deforestation, close contact with new hosts, and urbanisation.

Amblyomma pacae

A. pacae was first described in 1911 by Aragão. The tick has a subtriangular dorsal base of the capitulum, without cornua, and a hypostome with 3/3 dentition. The coxa I has two subequal and stout spurs, with the external one slightly longer than the internal one. The coxae II and III have a small and broad spur, while coxa IV has a short triangular spur. The trochanters and tibiae do not have spurs. The host of A. pacae is typically Cuniculus paca, or the lowland paca, whose range includes southern Mexico. The tick has also been found on wild pigs, peccaries, and Tamandua tetradactyla in Suriname and Venezuela.

A. pacae has been recorded in Belize, Brazil, Colombia, Costa Rica, Guyana, Panama, Paraguay, Suriname, Venezuela, and now Mexico. The finding of this tick species on Tapirus bairdii in Mexico is the first on this host.

Some Amblyomma species are known to be disease vectors, such as for Rocky Mountain spotted fever in the United States and ehrlichiosis in Brazil. However, further studies are needed to determine whether A. pacae acts as a vector for pathogens.

Amblyomma cf. oblongoguttatum

The Amblyomma genus is the third largest in the Ixodidae family. Species in this genus primarily occupy the torrid zones of all continents, with the centre of species diversity being on the American continent. Amblyomma species have been found in Eurasia, Africa, and Australia, in addition to the Americas. Some Amblyomma species are disease vectors, such as the vector for Rocky Mountain spotted fever in the United States.

Ehrlichiosis is an illness caused by the bacteria Ehrlichia, which is spread by ticks. It can be caused by the species E. chaffeensis, E. ewingii, and E. muris eauclairensis. Symptoms of ehrlichiosis include fever, muscle aches, headaches, and rashes. It can be treated with antibiotics, but can cause serious complications and even be life-threatening if left untreated.

Ixodes affinis

I. affinis is a member of the Ixodidae family, which is known for being hematophagous ectoparasites, or ticks that feed on blood. The Ixodes genus contains at least 245 species worldwide, 55 of which are found in the Neotropical region.

I. affinis has been the subject of recent studies due to its expanding range, which is changing the tick community population dynamics in the Mid-Atlantic United States. Surveillance in southeastern Virginia found that I. affinis populations tend to increase as ecological succession progresses and persist once established, provided there is a vegetated understory. The highest densities of I. affinis were found in mixed pine-hardwood forests with an herbaceous understory.

I. affinis is also notable for its role as an efficient sylvatic vector of Borrelia burgdorferi, the causative agent of Lyme disease. However, it is not known to parasitize humans.

I. affinis can be differentiated from the similar-looking Ixodes scapularis, which is a known human-biting vector of B. burgdorferi, by its morphological characteristics. When viewed dorsally, female I. affinis ticks lack cornua, while female I. scapularis ticks have moderate-sized cornua. Additionally, the mouthparts of female I. affinis are more triangular in shape, while those of female I. scapularis are more rectangular. The scutal punctations of I. affinis are large and deep, in contrast to the fine and evenly distributed punctations of I. scapularis.

Differentiation between male I. affinis and I. scapularis can also be made through the size and shape of the internal spur on coxa I and the density of setae. Male I. affinis have a thick, straight, and long internal spur, while that of I. scapularis is relatively short and slender. The scutal and idiosomal setae of I. affinis males are sparse, while I. scapularis males have an abundance of long, fine setae.

Rickettsia sp. strain Atlantic rainforest

The Rickettsia sp. strain Atlantic rainforest is transmitted by the tick species Amblyomma ovale, which has been found on domestic dogs in the aforementioned regions of Brazil. This tick species has also been identified as a vector for this Rickettsia strain in Colombia, where infected ticks were discovered on dogs and a rodent in Antioquia and Córdoba Provinces.

The infection caused by Rickettsia sp. strain Atlantic rainforest results in an inoculation eschar at the tick bite site. This was observed in a patient from southern Brazil, who presented with an eschar at the tick bite site on their left ankle, which evolved over time.

The gltA, ompB, and ompA gene fragments of the Rickettsia sp. strain Atlantic rainforest are 100% identical to the corresponding sequences of the original strain reported in southeastern Brazil. It also shares 100% sequence identity with the ompA sequence of strain Bahia, which was identified in the same area as the present study in Bahia state.

The role of Amblyomma ovale as a vector for Rickettsia sp. strain Atlantic rainforest in the Paty Valley area and other parts of Latin America is a subject of ongoing discussion.

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