Q Fever in cattle: what is its real prevalence?

q fever in cattle

Q fever also named coxiellosis is an infectious disease caused by an obligatorily intracellular bacterium, Coxiella burnetii. Many animals species including dogs, cats, rabbits, rodents, birds and even some arthropods are susceptible to be infected by this bacterium. But ruminants (cattle, goats and sheeps) are the main reservoir of the bacteria which can also contaminate humans.

Techniques to assess the prevalence of Q fever in cattle

There are several ways to assess the prevalence of Q fever in cattle:

  • It can be estimated at the herd level: what is the ratio of infected herds within a country or area? An infected herd being defined as a herd with at least one positive animal to Q fever.
  • But the prevalence can also be assessed at animal level: what is the ratio of positive animals in a country or a zone?

The figures given by these two ways can differ slightly. In extreme cases, the prevalence at herd level can be 100%: all the herds studied are infected. But at animal level, the prevalence can be lower. For example, in a study carried out in Egypt in 2012-2013, all the farm tested were infected but only 13% of the animals were positive (Gwida et al., 2014).

 

There are two main ways to evaluate the positivity of animals and herds. They can be gathered in two families:

  • Direct diagnosis: currently, direct diagnosis is carried out using molecular techniques and mainly rt-PCR or qPCR (real time Polymerase Chain Reaction or quantitative Polymerase Chain Reaction). These techniques can be used on several samples including feces, vaginal swab, placenta… and milk. This latest is of main interest as it includes bulk tank milk, which can be relevant for epidemiological studies in dairy cattle.
  • Indirect diagnosis (serology): the technique used is mostly ELISA (Enzyme Linked ImmunoSorbent Assay) as it is reliable and cost effective. But some other tests can also be used as ImmunoFluorescence or Complement Fixation Test. All these techniques aim to detect specific antibodies against Coxiella burnetii and can be performed on blood or milk, including bulk tank milk.

In the case of epidemiological survey both family of tests are relevant, but neither is absolutely perfect:

  • Direct diagnosis can underestimate the real prevalence because the shedding of Coxiella burnetii by the animals is intermittent. 
  • Indirect diagnosis can overestimate the real prevalence because antibodies can be found in blood or milk, even if the animals are no longer infected.

Q fever in cattle

Prevalence of Q fever in cattle

With the exception of New-Zealand, Coxiella burnetii is present worldwide

Several studies assessed the prevalence of Q fever in cattle in many countries, using serology or PCR. Depending on the study, the prevalence may vary slightly but the number of herds and animals affected is never negligible. 

The tables and maps below summarize the prevalence of Q fever in cattle according to data published in scientific literature over the last 30 years. The first table (table 1) and map (figure 1) show the prevalence at animal level while Table 2 and Figure 2 consider it at herd level:

Table 1. Prevalence of Q fever in cattle at animal level 

Country

Number of animals tested

Number of positive animals

Prevalence

Africa

28403

6163

21,7%

Cameroon

14754

4628

31,4%

Chad

442

29

6,6%

Egypt

1294

180

13,9%

Ethiopia

422

37

8,8%

Ghana

166

30

18,1%

Guinea

463

95

20,5%

Nigeria

1013

327

32,3%

Senegal

196

8

4,1%

South Africa

9231

723

7,8%

Togo

242

36

14,9%

Zimbabwe

180

70

38,9%

America

3225

464

14,4%

Canada

75

18

24,0%

Colombia

482

110

22,8%

Ecuador

2668

336

12,6%

Asia

9943

1619

16,3%

Bangladesh

620

4

0,6%

China

1395

412

29,5%

Iran

497

69

13,9%

Japan

562

262

46,6%

Korea

3077

177

5,8%

Lebanon

865

86

9,9%

Nepal

162

2

1,2%

Saudi Arabia

518

169

32,6%

Turkey

1488

161

10,8%

United Arab Emirates

759

277

36,5%

Europe

65477

8324

12,7%

Albania

863

81

9,4%

Bulgaria

16728

1498

9,0%

Cyprus

75

18

24,0%

Denmark

2188

625

28,6%

France

95

23

24,2%

Germany

25093

3468

13,8%

Hungary

697

271

38.9%

Ireland

5182

321

6,2%

Italy

1361

323

23,7%

Netherlands

7792

743

9,5%

Poland

2973

707

23,8%

Spain

2071

229

11,1%

Switzerland

359

17

4,7%

Oceania

4086

10

0,2%

Australia

1905

10

0,5%

New Zealand

2181

0

0,0%

Grand total

111134

16580

14.9%

 

Figure 1. Map of the prevalence at animal level

 

Table 2. Prevalence of Q fever in cattle at herd level

Country

Number of herds tested

Number of Positive herds

Global herd prevalence

Africa

182

119

65%

Cameroon

146

99

68%

Egypt

9

9

100%

Nigeria

27

11

41%

America

1779

1165

65%

Canada

222

83

37%

Columbia

11

5

45%

Ecuador

386

181

47%

USA

1160

896

77%

Asia

1617

324

20%

China

19

16

84%

Iran

642

70

11%

Jordan

78

55

71%

Korea

607

108

18%

Lebanon

173

53

31%

Turkey

98

22

22%

Europe

11166

4849

43%

Belgium

256

134

52%

Croatia

39

33

85%

Czech Republic

414

331

80%

Denmark

2476

956

39%

France

145

58

40%

Germany

173

108

62%

Greece

80

28

35%

Hungary

437

347

79%

Ireland

563

242

43%

Italy

1753

681

39%

Latvia

252

27

11%

Netherlands

991

519

52%

Poland

1171

323

28%

Portugal

90

26

29%

Serbia

72

42

58%

Slovakia

159

127

80%

Slovenia

48

28

58%

Spain

427

251

59%

Switzerland

872

344

39%

United Kingdom

748

244

33%

Oceania

49

6

12%

Australia

49

6

12%

Grand Total

14793

6463

44%

 

Figure 2. Map of the prevalence at herd level

These data highlight the high prevalence of Q fever in cattle. At animal level, it ranges from 0% in New-Zealand to 46,62% in Japan. On the other hand, the herd prevalence is very high in most of the countries. The study carried out in Egypt found that all the herds were infected. Even if it is an extreme case, globally the data available for 34 countries shows that for 27 of them, the herd prevalence is above 30%, and for 16 of them, above 50% meaning that at least 1 cattle herd out of 2 is contaminated by Q fever.

Key Message

Q fever is therefore a ubiquitous disease present in a large part of cattle herd around the world. But most of the infected farms are not aware about their status regarding Q fever. A better diagnosis and consequently a better control of the disease would lead to an improvement of cattle welfare and farm productivity and also to a lower risk of human contamination as Q fever is zoonotic disease.

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