Was there a link between human TB cases and the Bovine TB outbreak among cows in Madinah, 2007-2008?

In February 2007, a number of cases of Bovine Tuberculosis (BTB) were reported among cows in Madinah, Western Region of Saudi Arabia. A committee formed of representatives of Ministries of agriculture, Health, Municipality, Monetary, and Local Government conducted a large survey of cow farms and raw milk shops all over Madinah. Several control measures were taken, including closing of all raw milk shops, and destruction of whole cow herds in which a case had been discovered. Nine milk samples were examined in November 2007, 2 of which were positive for BTB. Over 100 human contacts of cows were examined (until April 2008), of which 15 were positive for skin test but not for chest X-ray. All human contacts with positive results were started on a full prophylaxis regimen and placed in a regular follow-up plan.

The total number of cow farms was estimated to be around 70 with 3,000 cows. On visiting them, most were found to be poorly structured and lacking even minimal health measures. Their supervisors were non-Saudis (most were Chadians) who practiced selling raw milk to homes after packing it in plastic bags without pasteurization.

There were a total of 27 raw milk shops in Madinah. According to the municipality, they are obliged to have a pasteurization machine as a requirement for obtaining their license. However, most of them used the "water bath" since they did not know the proper way of using the pasteurization machine.

On visiting the TB Hospital, 6 human TB cases who had been admitted for treatment were interviewed, two of whom gave a positive past history of consuming raw cow milk.

a cross-sectional study was conducted to investigate any epidemiological link between this bovine TB outbreak among cows and the registered human TB cases at the TB Hospital in Madinah. The study was conducted among all the registered human TB cases in TB office in Madinah (years 2007 and 2008). The total number of cases in 2007 was 159, and the number in 2008 (up to April 2008) was 53. Data was collected from patients by telephone or direct interview using a pre-designed questionnaire.

Participants consisted of 66 males (51.2%) and 63 females (48.8%). The majority were below 45 years of age (72.9%). Saudis constituted the majority (51.2%), followed by Chadians (10.9%), Pakistanis (7.7%), Mauritanians (6.2%), and other nationalities (24.0%). The vast majority (91.5%) were living in Madinah. The largest proportion was housewives (33.3%), followed by students (22.5%) and jobless (14.7%).

Ninety seven patients (75.2%) had pulmonary TB, and 32 (24.8%) had extra-pulmonary TB. Only 41 (31.8%) gave a history of BCG vaccination, 45 (34.9%) had not taken BCG, and 43 (33.3%) were uncertain.

Among the total study participants, 20 (15.5%) gave a history of close contact with one or more human cases, and 18 (14.0%) gave a positive history of contact with any type of cattle before illness (figure 1). Among those, 9 patients (50.0%) had been in contact with cattle for a long duration of 20 years, 3 (16.7%) for 30 years, and 2 (11.1%) for 5-years. The vast majority (122; 94.6%) gave a positive history of milk intake, of whom 47 (38.5%) consumed raw milk, while 75 (61.5%) consumed packed pasteurized milk (figure 2). Among the 47 who consumed raw milk, 15 (31.9%) obtained it from their own houses, 12 (25.5%) from vendors, 11 (23.4%) directly from farms, and 11 (23.4%) from milk shops. Regarding history of abnormal symptoms on cattle, 22.2% reported weight loss in their cattle, 16.7% reported chronic cough, and 5.6% reported sudden death of one or more of his/her cattle.

Tuberculosis (TB) is a contagious disease of both animals and humans. It is caused by three types of bacteria that are part of the Mycobacterium group: Mycobacterium bovis, Mycobacterium avium, and Mycobacterium tuberculosis.¹ Bovine TB is caused by M. bovis, a gram positive acid-fast bacterium. It is a significant zoonosis which can be transmitted from livestock to humans through aerosols and ingestion of raw milk. It has a very wide host range, where it can infect all warm-blooded vertebrates and humans. Bovine TB is of great economic importance to the livestock industry, due to losses from deaths, chronic disease, and trade restrictions.^1,2

The global prevalence of human TB due to M. bovis has been estimated at 3.1% of all human TB cases, accounting for 2.1% and 9.4% of pulmonary and extra-pulmonary TB cases, respectively.^2,3 In developed countries, bovine TB is subject to national control programs which significantly reduced its prevalence. However, wildlife reservoirs make complete eradication difficult in most of these countries. Only a few countries, such as Australia, Denmark, Sweden, Norway, and Finland, are considered to be free of bovine TB.^2,4 The disease is still common in less developed countries since surveillance and control activities are inadequate or unavailable. In Asia, 94% of human population lives in countries that undergo no control measures of bovine TB.^2,3

Links between bovine TB among cows and human TB cases have been reported. In a study conducted in Zambia, it was found that households who reported a TB case within the previous 12 months were approximately 7 times more likely to own herds containing tuberculin-positive cattle (OR = 7.6; p = 0.004).⁵

In Saudi Arabia, the prevalence of bovine TB among the cattle population is low. No significant outbreaks have been reported in the previous years. However, collaborative inter-sectoral actions were taken to control this outbreak as soon as it was discovered.

In this study, 14% of participants reported contact with cattle for many years before illness, and different activities in dealing with the cattle, such as grazing, feeding, milking, and cleaning. This finding is compatible with the situation in most developing countries, where cattle are an integral part of social life, and where they occupy an important part of housing, especially in rural areas.^2,3 Another interesting finding is that some participants reported symptoms similar to that of the disease among cattle (eg. weight loss, chronic cough, and sudden death).¹ This may be an additional indicator of a possible link between animal and human disease.

Consumption of raw milk is a major mode of transmission of bovine TB.^1,2,3 The current low prevalence and incidence of bovine TB in developed countries is mainly attributed to the widespread pasteurization of milk. The majority of cases of bovine TB in those countries are either due to reactivation of old disease or occupational exposure.⁶ In this study, more than 30% of participants gave a history of consuming raw milk before illness. Again, this finding may serve as an important indicator of a possible link. The largest percentage (31.9%) of participants who consumed raw milk was obtaining the milk from their own houses, followed by vendors, farms, and milk shops. This finding raises the importance of including houses in agricultural areas in future plans of surveillance of cattle disease. Furthermore, all farms and milk shops should be regularly checked by the Municipality for health measures. All workers in milk shops should be obligated to use pasteurization machines and should be trained on using them. The Health Department should regularly follow-up workers in shops and farms through tuberculin skin test and chest X-ray.

Bovine TB outbreak among cows in Madinah seemed to be under good control, since all the possible channels of transmission to humans were almost blocked. However, this study showed that there may be some possible indicators of an epidemiological link between the outbreak of bovine TB among cows in Madinah and the human TB cases. Those indicators include reporting a long past history of contact with cattle and consuming raw milk. However, these epidemiological indicators do not provide any confirmation of a link. A confirmatory laboratory test is therefore required to specify the strains of the isolated mycobacteria from cows and humans. The new technique of DNA fingerprinting of mycobacteria is the most useful tool to prove any link of disease in the two populations.⁷ TB surveillance among humans and all types of cattle in Madinah in the upcoming years is vital to follow the disease trend and evaluate control measures.

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