Porcine babesiosis

Porcine babesiosis

Porcine babesiosis

Previous authors: D T DE WAAL

Current authors:
D T DE WAAL - Associate Professor, BVSc, PhD, DipDatMet, HDipUTL, DipEVPC, MRCVS, School of Veterinary Medicine, University College Dublin, Room 034, UCD Veterinary Sciences Centre, Belfield, Dublin, D04 W6F6, Ireland

Introduction

Porcine babesiosis is a tick-transmitted, protozoal disease caused by either Babesia trautmanni or Babesia perroncitoi and characterized by fever, anaemia, icterus and haemoglobinuria. Babesia perroncitoi does not occur in southern Africa.

The disease was first reported in Russia in 1911 by Dementjew.8 According to Knuth and Du Toit the first reliable description of the disease was given by Trautmann, who studied the condition in Tanzania in 1914.8 The protozoan concerned was later named Babesia trautmanni.8 In 1939, Cerruti identified another protozoan parasite in the red blood cells of pigs in Italy that were exhibiting clinical signs of babesiosis, and he named this parasite Babesia perroncitoi.1 Babesia trautmanni also occurs in pigs in Ghana,17 Sardinia,  Zaire10 and Nigeria.3, 15 More recently, B. perroncitoi has been identified in pigs in China,6 Egypt,5 Ghana,17 and Senegal.23

In southern Africa, porcine babesiosis was described in 1948 in pigs near the Pongola River in the south-eastern region of the Limpopo Province, South Africa,7 and in Zimbabwe.9 It was also reported in 1958 in the Soutpansberg district in the Limpopo Province.13 In all three outbreaks the causative organism was B. trautmanni.

Although the disease is probably endemic in certain parts of the world, it is seldom reported and is not considered economically important.

Aetiology and life cycle

Babesia trautmanni is a large Babesia found in the red blood cells of infected pigs. The merozoites (which are usually paired) measure 2,5–4 × 1,5–2μm and are oval or pyriform in shape. Single forms, probably trophozoites, are amoeboid or round. The host cell usually contains between one and four parasites.

Babesia perroncitoi is smaller than B. trautmanni, the majority of parasites being pleomorphic, annular and measuring 0,7 to 2 μm in diameter.

A variety of other forms, such as oval, quadrangular, and pyriform, also occur. These vary in size from 1,2 to 2,6 μm in length and 0,7 to 1,9 μm in width.1

The life cycles of the organisms in the tick vector are as yet unknown.

Epidemiology

Porcine babesiosis has been reported in the former Soviet Union, Southern Europe, Africa,8, 16, 22 and more recently from China6 but has not been studied extensively and remains a neglected disease.

Clinical cases of babesiosis caused by B. trautmanni is seldom reported and have only been observed in domestic pigs in southern Africa and Italy. The bushpig (Potamochoerus porcus) has been shown to be capable of harbouring the parasite for at least 24 days after artificial infection, but without apparent disease occurring.20 However, wild boar sampled in Sardinia (Italy) all tested negative in an area that overlapped with that of domestic pigs that were found positive for B. trautmanni.24 Clinical cases of B. perroncitoi are rarely reported – the only recent case was from a farm in Inner Mongolia where 20 per cent of pigs died.6

The disease could potentially occur in those parts of the world where the tick vector(s) and in southern Africa where both bushpigs and tick vector(s) are found. Bushpigs are particularly associated with forests, thickets, riparian undercover, reed beds or heavy cover of tall grass where there is water.21 Agricultural developments have favoured them. In South Africa, bushpigs occur in the Limpopo Province, eastern parts of Mpumalanga, central and eastern KwaZulu-Natal, and along the coast in the Eastern Cape Province. They also occur in Zimbabwe, Botswana and Mozambique south of the Zambezi River. Bushpigs are widespread but do not occur in the more arid west of Zimbabwe, while in Botswana they are mainly confined to the Okavango Swamps and adjacent river systems.21 They have not been recorded in Namibia.21

Infection is probably endemic in domestic pigs kept under free-ranging systems of management in endemic areas, but clinical disease is rare. Although intensely farmed pigs are usually not exposed to the parasites, clinical cases of babesiosis may occur when they are turned out to pasture, or when infected ticks are introduced into pigsties via grass used for bedding.

Circumstantial evidence suggests that the ticks Rhipicephalus (Boophilus) decoloratus8 and R. turanicus14 are the vectors of B. trautmanni in Africa, and it has been successfully transmitted by R. turanicus11 as well as  R. simus.2

The nymph and adult progeny of experimentally infected female R. simus and R. turanicus ticks transmitted the infection to pigs. The prepatent period varied from 6 to 15 days after tick infestation. Attempts at transmitting the disease with Hyalomma marginatum, H. truncatum, H. marginatum rufipes, R. sanguineus, R. maculatus, R. rossicus, Amblyomma hebraeum and Dermacentor silvarum have failed.11, 14 The possibility of mechanical transmission by haematophagous flies, such as tabanids and Stomoxys spp., has been suggested.3

Although not proven, R. sanguineus, D. reticulatus and H. aegyptium have been suggested as vectors of B. perroncitoi in Europe.1

Clinical signs and pathology

Babesiosis caused by B. trautmanni is a mild disease4, 12, 13 which, in endemic...

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