The postmortem examination

It is always important to plan well. A hastily performed necropsy, with inadequate notes or unrepresentative samples, may yield data that are confusing, useless, or even erroneous.

The steps that should be taken in preparing for a postmortem examination are as follows:

1. Decide why the necropsy is to be carried out. The various types of postmortem examination, which have different objectives, are summarized in Table 8.3.

184 | Information from dead and dying birds Table 8.2 Methods of euthanasia of birds

Method

Comment

Physical3

Chemicalb

Dislocation of neck

Pressure on sternum

Striking the cranium on a hard surface

Other

Overdose of injectable anesthetic agent such as sodium pentobarbitone

Overdose of an inhalation anesthetic agent, for example, halothane, isoflurane

Exposure to 100% carbon dioxide

Generally for larger birds (waterfowl, herons, etc.) of up to 3 kg only Needs training or experience

For small birds (less than 100 g in weight) only

Must be immediate. For small birds (up to 23 g)

Large birds can be killed by striking on the head with a suitable heavy instrument but skill is needed

For best results a barbiturate should be given intravenously but this requires skill. Intraperitoneal (intracoelomic) administration is easier but death is not instantaneous and internal organs may be damaged

Requires the use of an anesthetic chamber for small birds or a mask for larger birds

As above (chamber). Suitable for large numbers of small birds a All physical methods cause damage, which may hamper postmortem examination, and may prove aesthetically unacceptable.

b The majority of chemical methods require the possession of potent anesthetic agents, most of which can only be obtained on veterinary prescription. Argon gas is now being used instead of carbon dioxide in UK poultry hatcheries for reasons of human health.

2. Check that appropriate facilities and equipment are available, including protective clothing and other means of reducing the risk of spread of infectious disease (see later).

3. Be sure that the person carrying out the postmortem examination is sufficiently knowledgeable about the techniques.

4. Do whatever "homework" is possible beforehand—for example, by obtaining relevant information about the normal anatomy of the species (Harcourt-Brown 2000: King and McLelland 1984) or its biology and natural history (Cooper 2003b). Seek advice if necessary.

Table 8.3 Types of postmortem examination

Purpose

Category

Comment

To determine the cause of death

Diagnostic

Routine diagnostic techniques are followed

To ascertain the cause of ill-health (not necessarily the cause of death)

Diagnostic/ health monitoring

Usually routine—but detailed examinations and laboratory tests may be needed to detect nonlethal changes

To provide background information on supposedly normal birds on the presence or absence of lesions, parasites, or of other factors, such as fat reserves or carcass composition

Must be methodical if information is not to be missed

To provide information for a legal case or similar investigation—for instance, on the circumstances of death or the possibility that the bird suffered pain or distress while it was alive

Forensic/legal

Can be very different from the categories above. The approach depends upon the questions asked. There must be a proper "chain of custody" and all material must be retained

For research purposes, such as removal of tissue samples or examination of organs

Investigative

Depends upon the requirements of the research worker

8.3 Health and safety

Dead and dying birds can present hazards to those who are involved in the investigations. Sometimes the dangers are physical—for example, the risk of injury while capturing live birds or retrieving dead ones from marshes—or chemical, because of contact with formaldehyde—but the most important category are the "zoonoses." These are often defined—for example, by the World Health Organization (WHO)—as "diseases and infections that are naturally transmissible between vertebrate animals and humans" but increasingly there is a tendency to consider zoonoses as any disease or infection that can be acquired by humans from animals (for a review of zoonotic infections, see Cooper 1990 and more recent specific publications, relating to "new" hazards such as West Nile virus). A useful general reference text on zoonoses, which includes data on both animals and humans, is the book edited by Palmer etal. (1998).

With zoonoses the picture is constantly changing. Infectious agents that were once not considered to be important in humans are now recognized as being potentially pathogenic. Many ofthese "opportunists" take advantage of a debilitated host—in particular, a person who is immunosuppressed. Immunosuppression in humans can result from an infectious disease (HIV/AIDS is the best known example but there are many others, such as malaria), malnutrition or some form of medication which is reducing the immune response. It is therefore wise to assume that sick or dead birds represent a source of pathogens for humans. If this precautionary approach is followed, and appropriate safeguards are taken, the risks involved in carrying out an examination of the bird will usually be low.

The specific precautions that should be implemented to minimize the spread of zoonotic infections depend on the circumstances. In some countries health and safety legislation may require the employer of those embarking upon postmortem examinations or sample-taking to compile a risk assessment before the work is done. The avian biologist or veterinarian who is likely to be involved in such work will need to follow the rules and to take appropriate precautions. In other countries, adherence to the same level of risk assessment and protection of staff will probably not be possible. Nevertheless, the scientist who is involved in such work, regardless of the country involved, has a moral responsibility for assistants and other staff, and it is therefore wise to draw up and adhere to a code of practice aimed at minimizing the risk of infection. A similar approach is usually needed in the field, where good facilities for the examination of birds are seldom available and improvisation is necessary. Again, in some countries there are health and safety obligations on employers and employees relating to field work but elsewhere these may not exist and instead a voluntary code of practice may need to be instigated (Cooper 1996). This is further discussed later, under 8.7 (Legal Aspects).

Basic rules that will help to reduce the spread of zoonoses are as follows:

• Be aware of the risks from birds, by reading the literature and by consulting veterinarians, physicians, and others who have the appropriate knowledge

• Familiarize colleagues and others involved in the study with the possible hazards

• Draw up a risk assessment, even if this is not a statutory requirement where you are working; follow this with a Standard Operating Procedure (SOP) in order to reduce the risks to a minimum

• Ensure that you and your colleagues understand how microorganisms can be spread and how best such spread may be prevented

• Operate the "clean/dirty" principle; whereby during a postmortem examination one person keeps "clean" and handles only the note-books, tape recorder, and the outside of specimen bottles, while the other is "dirty" and comes into direct contact with the dead bird and its tissues.

• Seek professional advice where the risk appears to be substantial—if for example, chlamydiosis (chlamydophilosis) is suspected or if the picture suggests a new or unusual infectious agent.

• Always follow basic hygienic precautions, such as the wearing of gloves and the use of disinfectants, and be prepared to invest in specialized equipment and facilities (which can range from facemasks to safety cabinets) if this is deemed necessary.

• If, during the course of a postmortem examination, an accident occurs (e.g. splashing of possibly infected material on to the face), seek medical advice. Likewise, if clinical signs that may be suggestive of a zoonotic infection occur following a necropsy, report this and detail the work that you have been doing.

• Consider producing a card that can be shown to and read by a member of the medical profession, explaining that the holder comes into contact with sick or dead birds and, therefore, in the event of an unexplained fever, or other clinical signs, might be infected with an avian pathogen.

• Remember if working overseas or as part of an international team that there may be barriers on account of language, especially amongst support staff. Consider using diagrams and other visual aids in protocols and literature as well as the written word.

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