Brucellosis can exist undetected for some period of time in low prevalence states unless all parts of the surveillance systems are operating properly. Alabama’s key surveillance tools are first point of concentration testing, change of ownership testing, the brucellosis ring test, epidemiological tracing, and diagnostic testing.

Recently in Alabama, two instances of brucellosis occurred and infected herds in this outbreak were not identified by the basic surveillance methods. The first of the two instances of brucellosis occurred during l993 in Chilton County, Alabama. The second outbreak occurred during late l994 in Covington County, Alabama.

Figure 1 illustrates five brucellosis infected herds involved in the Chilton County outbreak and their relation to spread of the disease. The Price Herd is the Index Herd from which brucellosis was spread to the four other herds.

8 Reactors

Figure 2 outlines the epidemiological investigation and the events involved in spreading the disease in Chilton County.

CHILTON COUNTY, ALABAMA

1993

 

 

HERD A (CLACKLER)

One MCI reactor 9-8-93. Biovar I isolated.

Herd test - 18 neg (2 locations).

Epid - Reactor home raised 6 year old normal calf 1992.

Rebred but no calf in 1993. Other cattle in neighborhood.

Herd A depopulated.

Traced 5 head sold.

INDEX HERD (PRICE)

Located 1/2 mile from Herd A.

Herd test - 8 reactors/42 head (2 locations). All reactors on location near Herd A.

Biovar I isolated.

Epid - Sold out previous herd in 1991. Restocked with 62 heifers from stockyards on five sale dates December 1991 - March 1992. One group of 18 came from stockyard where MCI reactors were found that day and is most probable source of exposure. Noted abortions and other calving problems beginning October/November 1992 - called veterinarian who considered these "normal losses" and did not visit to test/diagnose. Sold 18 of these bred "exposed" heifers February 1993 through stockyard and spread infection to Herds B, C, and D.

Index herd is most probable source of infection for Herd A by neighborhood spread.

Index Herd depopulated.

Traced sales of 45 head.

HERD B (MIMS)

Bought 6 bred heifers through stockyard February 1992 originating from Index Herd.

Herd test - 4 reactors/92 head (3 groups). Two were from Index Herd purchase and calved normally.

Herd B depopulated.

Traced sales of 23 head.

HERD C (TYLER)

Bought 2 bred heifers through stockyard February 1992 originating from Index Herd.

Herd test - 2 reactors/138 head (2 groups). One was from Index Herd purchase which had a full term dead calf. One separate group negative.

Herd C depopulated 2 groups. Adult vaccinated other negative group.

Traced sales of 17 head.

HERD D (ABRAMS)

Bought 4 bred heifers through stockyard February 1992 originating from Index Herd.

Herd test - 2 reactors/15 head. One was from Index Herd purchase. Biovar Isolated. Two other groups negative and adult vaccinated. One negative group and an earlier undisclosed group tested later and had reactors.

Herd D depopulated all infected groups.

SUMMARY OF OUTBREAK

Number of Herds with reactors - 5

Area test initiated in Chilton County approx. 3-mile radius from infected herds. Area encompassed approximately 50 square miles. One hundred and nine herds (109) containing 2,002 cattle tested. No further reactors found.

Two negative high risk neighbor herds were adult vaccinated.

Tracing of sales from infected herds did not yield reactors.

Total cattle depopulated - 459

Total indemnity - $69,350.00

Factors contributing to spread of brucellosis in the Chilton County outbreak:

- probably initial exposure occurred at a livestock market in purchased heifers.

- failure of the herd owner’s veterinarian to make a farm call to test or diagnose cause of animals owner reported as aborting.

- sales of exposed first calf heifers in mid pregnancy through a livestock market that were tested but were not yet showing titer.

If brucellosis had been diagnosed early in the Index Herd (Price) by the herd owner’s veterinarian it would have prevented infection from spreading to four herds with 4l0 animals having to be depopulated, costing $6l,800 indemnity and the necessity of considerable area testing.

A second outbreak of brucellosis occurred in Covington County, Alabama, in late l994. Figure 3 illustrates the five infected herds and their involvement in spreading brucellosis. The Davis Herd in the Index Herd of this outbreak that caused the spread of brucellosis to four other herds.

Figure 4 illustrates the findings of the epidemiological investigation and the events involved in the spread of brucellosis in the Covington County outbreak.

Herd A (Johnson)

One MCI Reactor on 11-9-94

Herd Test - Two reactors/23 on 11-22-94. Biovar I isolated.

Epidemiology - Five Beefmaster heifers purchased August 1993 - One aborted during summer 1994. Purchases traced to Index Herd.

Herd A depopulated December 1994

Community testing - Four owners with eight groups of cattle containing 456 animals tested (one fence line herd was adult vaccinated).

Index Herd (Davis)

Herd Tests - #1 27 rea/140 on 12-8-94. Biovar I isolated. #2 47 negative on 12-15-94

Epidemiology- Herd has been on this farm since 1992. Came from Baldwin County. Beefmaster cattle appear to be origin of problem. 52 Beefmaster heifers (CV) and one bull brought from Texas in 1989. Texas county of origin had significant level of infection in 1989. Other aspects concerning source of infection have been investigated.

Sold cattle to Herd B and Herd C in addition to Herd A.

Index Herd depopulated December 1994.

Community Testing - 22 owners with 28 groups of cattle containing 659 animals tested.

One fence line contact herd adult vaccinated but found to be infected (Herd D).

Herd B (Wright)

Herd Test - One rea/19 on 12-19-94. Biovar I isolated.

Balance of owners’ herds in other locations - 77 neg.

Epidemiology - 14 BM females bought from Index Herd in August 1993. The singleton reactor was one of these and had never calved.

Herd B depopulated the infected group and several other exposed cattle (young heifers primarily) in December 1994. Balance of herd under quarantine and further testing for 180 days.

Community Testing - Three owners with three groups of cattle containing 43 head tested.

Herd C (Dobbins) - Located in Dekalb County

Herd Test - One rea/7 on 12-17-94 (at stockyard).

Balance of herd - 64 neg. on 12-22-94.

Epidemiology - Eight BM cows bought from Index Herd in September 1994. One had died and remaining seven removed from herd after tested at stockyard enroute to slaughter as indicated above. Reactor had not calved. Herd under quarantine and further testing for 120 days.

Herd C depopulated the seven head as shown in December 1994.

Community Testing - One owner with one group of cattle containing 16 animals tested.

Herd D (Barefoot)

Herd Test - One rea/25 on 12-26-94.

Epidemiology - Herd was fence line contact with Index Herd and was adult vaccinated at time of test. Treated with Ivermec.

To depopulate 2-14-95 (Ivermec withdrawal time).

Community Testing - Included with Index Herd.

Summary of Outbreak

Number of Herds with reactors found - 5

Totals of community testing - 29 owners with 39 groups of cattle containing 1,158 cattle tested.

Total cattle depopulated and indemnity amount - 332 head, $123,702.36

Sales of cull cattle and heifers from Index Herd and Herd A through stockyard and other purebred activity of Index Herd being traced.

Further epidemiological work done as to possible sources of infection of Index Herd. Previous location in Baldwin Co. where Index Herd cattle were located 1989-92 was investigated and with one herd remaining to be tested (as of 4-1-95) does not appear to be source or spread of infection. Most probable source appears to be exposure in the heifers when purchased from Texas prior to movement to Alabama.

Had the change of ownership testing been conducted, the disease would have been detected early and would have prevented spread to four herds with l33 animals depopulated costing $43,474.00 indemnity profits. This would also have prevented widespread community spread.

Factors involved in spreading brucellosis in the Covington County outbreak:

- probably exposed heifers purchased from an area with a high brucellosis infections rate at time of purchase in l989.

- MCI surveillance did not detect infection since sales through livestock markets were young non-test eligible animals.

- failure of owner to have change of ownership test conducted when selling cattle by private treaty to several individuals.